The authors have no acknowledgements.

This study was approved by the local institutional review boards at all participating centers. All subjects in the multicenter trial provided written informed consent to participate in eTRIS at their respective institutions.
1. Image Acquisition
<ol>
	<li>Perform the MR imaging on a 1.5 T or 3 T whole body scanner using specialized phased-array coils for MRV such as a peripheral vascular coil, body matrix coils or run-off coils. Use these coils in conjunction with other body matrix coils or spine coils. If no suitable specialized coils are available, use the body coil instead. 
	NOTE: Use commercially available scanners such as Siemens Symphony, Sonata, etc.
	<ol>
		<li>Screen subject, and review MRI safety questionnaire prior to scan. Have subject change into a gown.</li>
	</ol>
	</li>
	<li>Place an intravenous line in the antecubital vein of subject for the injection of the contrast agent. Follow standard safety procedures for injecting a gadolinium-based contrast agent.</li>
	<li>Place subject in supine, feet first position in the MRI machine and position appropriate coils on regions to be scanned. Secure coils using Velcro straps as needed.
	<ol>
		<li>Fasten subject’s legs/feet to prevent motion artifacts during the MRI scan.</li>
		<li>Turn on the centering laser and move the table until the laser crossbeams are located just below the subject’s knees (patella). Accept this position for the iso-center of the scan and move the patient table to the center position of the scanner bore.</li>
	</ol>
	</li>
	<li>Measure the creatinine clearance (CrCL) and determine the dose of the contrast agent to be used for the subject based on body weight. If CrCL &lt;30 ml/min, subject is excluded from the study. For individuals with CrCL &gt;30 ml/min but less than 45 ml/min, 0.01 mmol/kg of contrast agent is used. For individuals with CrCL &gt;45 ml/min but &lt;60 ml/min, 0.02 mmol/kg of gadofosveset is injected. For individuals with normal renal function (creatinine clearance &gt;60 ml/min), a dose of 0.03 mmol/kg (0.12 ml/kg) gadofosveset trisodium is used. An MRI compatible power injector is used to inject the contrast agent.</li>
	<li>Perform bilateral imaging of both legs and lower pelvis in a single examination session lasting approximately 60 min as shown in Table 1 and described in MRI protocol section. 
	NOTE: Anonymize patient data prior to transfer of images to a central core laboratory for analysis.</li>
</ol>
2. MRI Protocol
<ol>
	<li>Execute the imaging protocol from the scanner console by selecting each protocol step from the protocol window and dragging it to the execution list. Once ready, run the sequence by pressing Scan/Execute or equivalent button.</li>
	<li>Acquire 2D gradient echo based sequences using sequence parameters in Table 1, in the three orthogonal axes to image from mid-calf to above the iliac crest and use as localizers/scouts.</li>
	<li>Perform time of flight (TOF) angiography scans in each segment as specified in Table 1 
	NOTE: These scans are also used as localizers to help differentiate arteries from veins as a long circulating contrast agent is used in steady state in this protocol. This view of the arterial tree is quite limited and only serves to help the image analyst differentiate the arteries from the venous vasculature and does not serve as a full-fledged angiogram.</li>
	<li>To avoid acquiring poor quality images at the inferior and superior extent of the imaging volume, acquire three coronal 40 cm segments in the foot to head direction overlapping by 10 cm during the 3D T1-weighted Gradient Echo scans. 
	NOTE: These three segments encompass: a) mid-calf to above knee b) above knee to thigh/lower pelvis, and c) thigh/pelvis to abdomen. Figure 1 shows sample images with the three acquisition locations illustrated.</li>
	<li>To distinguish between acute and chronic venous thrombosis, acquire T1W direct thrombus imaging (DTHI) and 3D gradient echo (GRE) sequences using parameters in Table 1. 
	NOTE: These 3 scans also serve as the pre-contrast scan for the MRV acquisition. The extent of the coverage of these acquisitions is the same as the initial localizers acquired in the three locations illustrated in Figure 1. GRE sequence is also easily implementable on various scanning platforms and across imaging field strengths.</li>
</ol>
<img alt="MRI analysis of leg showing potential muscle abnormalities; transverse and longitudinal views." src="/files/ftp_upload/52761/52761fig1.jpg" data-altupdatedat="1747911167000" data-alt="Figure 1"> 
Figure 1: Sample images showing acquisition locations for the 3 stations used for imaging. The field of view in the coronal direction and axial directions was 40 cm for each bed position [acquisition: (mid-calf to above knee), (above knees to thigh/pelvis), (thigh/pelvis to abdomen)] with 10 cm overlap between each bed position. (a) axial image; (b) sagittal image and (c) coronal image. Red arrow indicates DVT. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52761/52761fig1highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol start="6">
	<li>Administer the contrast agent (gadofosveset trisodium) at a dose of 0.03 mmol/kg (0.12 ml/kg) intravenously into the subject at a rate of 2 ml/sec and flush with 20 ml of saline. Let the contrast agent circulate for 5 min to ensure a steady state in the blood pool.</li>
	<li>Acquire MRV images; post contrast 3D gradient echo sequences at 3 locations described previously. See the sequence parameters in Table 1 and Table 2. Use these images to determine the locations and size of the thrombi.</li>
</ol>
<img alt="MR imaging protocol table, detailing scan sequences, planes, and parameters for thrombus detection." src="/files/ftp_upload/52761/52761table1.jpg" data-altupdatedat="1747911167000" data-alt="Table 1"> 
Table 1: Lower extremity MR venography protocol with the contrast agent, gadofosveset trisodium, including direct thrombus imaging.
<img alt="MRI sequence parameters table for GRE and spoiled GRE with details on TR/TE, resolution, and flip angles." src="/files/ftp_upload/52761/52761table2.jpg" data-altupdatedat="1747911167000" data-alt="Table 2"> 
Table 2: The specific imaging parameter for each sequence acquired in the protocol.
<ol start="8">
	<li>After scan is completed, remove subject from the MRI scanner and take out the intravenous line. Ask the subject to change out of gown and exit the facility.</li>
</ol>
3. Image Analysis
<ol>
	<li>Perform image analysis on a dedicated image analysis workstation running FDA-approved open source image processing software such as OsiriX MD20, by 2 trained image analysts. Ensure the analysts have a minimum of 3 years experience each.</li>
	<li>Temporarily blind all images before transfer to the image analyst workstation for analysis.</li>
	<li>Ensure that a radiologist assesses each MRI scan for the presence and location of thrombi. Provide the radiologist’s assessment to the image analyst to be used as a guideline throughout the analysis.</li>
	<li>Load all DICOM images from both MRI visits of a subject into the image processing software by selecting “import”, and compare the two imaging time-points of the MRV series for each subject to ensure adequate spatial coverage and registration across time points.
	<ol>
		<li>Select the “3D MPR” tool in viewer to provide simultaneous browsing of image data in 3 orthogonal views (axial, coronal, and sagittal). 
		NOTE: The image processing software’s 3D MPR mode enables the viewing of the vessels of interest.</li>
	</ol>
	</li>
	<li>Analyze the following vessels if DVT is present: external iliac, common femoral, superficial femoral, deep femoral, popliteal, anterior tibial, posterior tibial I &amp; II, gastrocnemius I &amp; II, and peroneal I &amp; II veins. All analysis is restricted to regions of the vessels that are present in images from both time-points.</li>
	<li>Assess the quality of the image for each vein with known DVT as indicated by the radiologist’s assessment on a 0-5 scale, with 0-2 being unanalyzable and 3-5 being analyzable for both the DTHI and MRV sequences. For the breakdown of scoring system see Figure 2.</li>
</ol>
<img alt="Vein image quality scoring criteria table with artifact, SNR, and delineation analysis from 0 to 5." src="/files/ftp_upload/52761/52761fig2.jpg" data-altupdatedat="1747911167000" data-alt="Figure 2"> 
Figure 2: The breakdown of the scoring system used for assessing the quality of images for each vein of interest with known DVT.
<ol start="7">
	<li>For MRV analysis, analyze each vessel individually. After 3D curved multiplanar reconstruction, use contours following the centerline of each vein, traced by the analyst, to generate curved path for each vein and save to file.
	<ol>
		<li>Establish the position of the thrombus in the three dimensional space. From the Curved MPR plane, a 3D Bezier path will be displayed.</li>
		<li>Delineate the centerline of the vein by selecting of the “Contour Path” tool in “Creation Mode”.</li>
		<li>Place points repeatedly on any of the orthogonal MPR view to straighten the entire vessel of interest.</li>
		<li>Make adjustments when necessary to ensure that the vessel is entirely straightened in “Editing Mode”</li>
		<li>When the contour path is accurately delineated at centerline of vessel, save by selecting the “curved path” icon to export the file</li>
		<li>Generate 1 mm axial slices perpendicular to the curved path and save as DICOM files (Figure 3). Observe the the curved path, straightened vessel, and corresponding axial images for quantifying DVT from MRV images. 
		NOTE: The images rendered in the 3D Curved MPR viewer must then be exported in DICOM format and added to the database as a new series of images.</li>
	</ol>
	</li>
</ol>
<img alt="MRI cross-section diagram with sagittal and axial views showing labeled muscle tissues and anatomical segments." src="/files/ftp_upload/52761/52761fig3.jpg" data-altupdatedat="1747911167000" data-alt="Figure 3"> 
Figure 3: Sample DVT shown on MRV sequence. (i, left panel) Curved path (yellow line) illustrates the contour followed by the vein being analyzed. (ii, middle panel) Straightened vessel along centerline of vessel being analyzed (red dotted line) (iii, right panel) shows axial slices perpendicular to vein being analyzed at locations indicated by yellow lines (A, B, C) on longitudinal sections. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52761/52761fig3highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol start="7">
	<li>
	<ol start="7">
		<li>On these axial DICOM images, manually segment regions of interest encompassing the thrombus (see Figure 4) by using the “Closed Polygon ROI Tool”. Save regions of interests to file by selecting the “Save all ROIs of this Series” located in the “ROI” drop down menu and save ROI metrics by navigating to the the “Plugins” menu and select “ROI Tools” followed by “Export ROIs”. This should be saved in a CSV format.</li>
	</ol>
	</li>
</ol>
<img alt="MRI scan sequence with tumor highlighted for medical analysis; series of three cross-sectional images." src="/files/ftp_upload/52761/52761fig4.jpg" data-altupdatedat="1747911167000" data-alt="Figure 4"> 
Figure 4: Manually segmented regions of interest (green) are shown encompassing the thrombus on axial reformatted DICOM images. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52761/52761fig4highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol start="7">
	<li>
	<ol start="8">
		<li>Calculate thrombus volume by multiplying the area on each analyzed slice by the slice thickness (1 mm) using a custom built Matlab script. Calculate total thrombus volume in each subject by adding the thrombus volumes in each vessel.</li>
	</ol>
	</li>
	<li>For DTHI analysis, identify fresh thrombus as bright regions on pre-contrast T1W 3D gradient echo scans13 within the DVT regions segmented by the MRV.
	<ol>
		<li>On axial pre-contrast images, compute the volume of fresh thrombus by drawing regions of interest (ROI) manually as shown in Figure 5. In Figure 6, sample images indicating DVT measured by DTHI in conjunction with the MRV images are depicted.</li>
		<li>Open the pre-contrast and post-contrast sequences alongside each other. Select “axial” view and delineate bright regions along the vessel of interest using the “closed polygon ROI Tool”.</li>
	</ol>
	</li>
</ol>
<img alt="MRI scan showing muscle anatomy with arrows indicating regions of interest, medical imaging analysis." src="/files/ftp_upload/52761/52761fig5.jpg" data-altupdatedat="1747911167000" data-alt="Figure 5"> 
Figure 5: Sample DVT shown on DTHI imaging sequence. (a) coronal image, (b) axial image, and (c) axial image showing region of interest (green) traced around fresh thrombus (blue arrows) on pre-contrast images. The DTHI images are acquired prior to the injection of contrast agent and rely on met-hemoglobin content of thrombus to produce bright signal.
<img alt="MRI knee cross-section showing MRV and DTHI methods, comparative imaging, medical analysis." src="/files/ftp_upload/52761/52761fig6.jpg" data-altupdatedat="1747911167000" data-alt="Figure 6"> 
Figure 6: Sample DVT shown on DTHI imaging sequence. The left panels show MRV images with signal voids indicating total DVT (green arrows). The right panel show corresponding DTHI images with bright signal indicating presence of fresh thrombus (blue arrows). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52761/52761fig6highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
4. Assessment of Reproducibility
<ol>
	<li>Evaluate a subset of ten subjects for the reproducibility of the analysis.</li>
	<li>Perform analysis, as described above, by two separate image analysts (primary and secondary readers) to assess inter-observer variability</li>
	<li>Ensure that primary reader also performs a second image analysis three months after the first analysis to assess intra-observer variability of the results.</li>
	<li>Compute intra-class-correlation coefficients (ICC) and perform a Bland-Altman analysis to assess inter and intra-observer reproducibility. Carry out a one sample t-test to look for bias on Bland-Altman analysis. ICC &gt;0.9 and no bias on Bland-Altman analysis are considered acceptable.</li>
</ol>

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A., Gizewski, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+Extracellular+Gadolinium-based+MRI+Contrast+Agents+and+the+Risk+of+Nephrogenic+Systemic+Fibrosis.">Application of Extracellular Gadolinium-based MRI Contrast Agents and the Risk of Nephrogenic Systemic Fibrosis.</a> Rofo. , (2014).</li><li>Alhadad, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Safety+aspects+of+gadofosveset+in+clinical+practice+-+analysis+of+acute+and+long-term+complications.">Safety aspects of gadofosveset in clinical practice - analysis of acute and long-term complications.</a> Magn Reson Imaging. , (2014).</li></ol>

Venkatesh Mani has received research grants from Novartis. Nadia Alie, Sarayu Ramachandran, Cecilia Besa, Philip Robson and Bachir Taouli have nothing to disclose. Michele Mercuri and Michael Grosso are employees of Daiichi Sankyo. Greg Piazza has received research grants from Daiichi Sankyo, BMS, EKOS, and the Thrombosis Research Institute. Samuel Goldhaber has received grants from BMS, Daiichi Sankyo, EKOS, NHLBI and the Thrombosis Research Institute. He is a consultant for Ariad, Bayer, Boehringer Ingelheim, Bristol Myers Squibb, Daiichi Sankyo, Genentech, Janssen, Merck, Pfizer and Portola. Zahi Fayad has received research grants from Daiichi Sankyo, Roche, GlaxoSmithKline, Merck, VBL Therapeutics, Novartis, Bristol-Myers Squibb, and Via Pharmaceuticals.

This study demonstrated the feasibility of quantification of deep vein thrombosis on MR venography using gadofosveset trisodium as a contrast agent, with excellent reproducibility of analysis for quantifying thrombus volume in a multicenter setting. To compute total thrombus volume, the primary method utilized the post-contrast MRV scan to measure thrombus volume. The secondary method used was the direct thrombus imaging approach (DTHI), which leverages the presence of met-hemoglobin within a fresh thrombus to produce a bright signal on a T1W MR image13,14. The MRV volume measures were highly reproducible. The DTHI approach had less reproducibility. The DTHI images were acquired without the use of any contrast agent injection, and intrinsically had poorer contrast to noise ratios for delineating thrombus as they rely only on met-hemoglobin content within thrombus to produce an MR signal. The thrombus volumes observed were comparable to those obtained in previous studies with ultrasound and other imaging modalities21.
We used a 3D gradient echo acquisition for imaging. 3D imaging with isotropic voxels allows for multi-planar image reformatting. These images have fewer partial volume artifacts as compared to 2D acquisitions and may therefore result in more accurate DVT quantification. The use of MR venography addresses some of the drawbacks inherent to the current imaging methods used for diagnosing and monitoring DVT. CUS is ideal to be used as a screening tool, since it is inexpensive and has high sensitivity and specificity to detect acute DVT5. However, CUS cannot reliably assess the proximal deep veins in the thigh and lower pelvis, which are the most common sources of PE22. Additionally, CUS cannot directly quantify thrombus volume and composition, which are important when distinguishing between acute DVT (a potential source of PE) and chronic DVT (less likely to embolize) and for evaluation of therapeutic efficacy23. Alternatives to CUS include venography techniques (X-ray or computed tomography, CT) to detect thrombi as constant intra-luminal filling defects after contrast material infusion. X-ray venography is invasive, costly, and rarely used2,4. CT venography has gained recent interest for the evaluation of DVT and PE during the same imaging session. However, CT scans involve ionizing radiation and carry the risk of contrast nephropathy. Furthermore, while the sensitivity/specificity of CT is similar to CUS, its diagnostic value and potential to quantify and characterize the extent of thrombosis have not been well established24.
Our MRV and DTHI methods have limitations. No modifications can be made to the protocol as this can compromise the quality of the images obtained and distort the positioning of the scanning regions. MR imaging is expensive and unlike ultrasound, is not portable. Individuals with hip/knee replacements and other metal implants such as screws cannot be imaged if the material is made of ferromagnetic substances. The use of Gd-based contrast agents is also contraindicated in individuals with impaired renal function due to nephrogenic systemic fibrosis (NSF)25. The contrast agent we used, gadofosveset trisodium, appears to have the lowest rates of NSF of all the Gd-based agent in the market16,26. This protocol is also acquired in a multicenter setting on scanners of different imaging vendors and field strengths. This makes the acquisition parameters not identical at all sites and may contribute to reduced robustness of results. It is also possible that thrombus size as measured by volume may not be linearly related to disease evolution but rather only provide clues about the evolution of the thrombus.

Venous thromboembolism (VTE) affects 300,000-600,000 individuals in the United States every year1. Deep vein thrombosis (DVT) is the most common presentation of VTE, and most commonly affects the calf, thigh or pelvic veins. The diagnosis, management, and follow-up of subjects with DVT cannot be based solely on clinical examinations, since the signs and symptoms of this disease are non-specific2,3. While blood tests (such as D-dimer) can help rule out the diagnosis of DVT, imaging is required to establish the presence of DVT4. Compression ultrasound (CUS) is currently the most commonly used imaging test in the diagnosis of suspected acute DVT. CUS is inexpensive and has high sensitivity and specificity to detect acute DVT5. However, CUS cannot reliably assess the deep veins in the pelvis6. Additionally, CUS cannot directly quantify thrombus volume and composition, which are important when distinguishing between acute DVT (a potential source of pulmonary embolism (PE)) and chronic DVT (less likely to embolize) and for evaluation of therapeutic efficacy7.
Unlike computed tomography (CT), magnetic resonance imaging (MRI) does not deliver ionizing radiation, and is therefore suitable for serial examinations to evaluate thrombus evolution or regression. Compared with CUS, MRI can detect pelvic DVT and can more precisely define proximal (popliteal vein and above) and distal leg (below popliteal vein) DVT8, to better assess the risk of PE. MRI can characterize thrombus age and organization, and may help differentiate acute from chronic DVT9-11 (refs updated). Quantification of thrombus volume, an important metric to assess the disease evolution and response to treatment, is feasible with MR imaging. Current magnetic resonance venography protocols are performed after injection of gadolinium (Gd) based contrast agents12. These are small molecular weight molecules that extravasate quickly after injection, and require careful timing to capture the venous enhancement phase needed to correctly visualize the thrombus13,14.
A proof-of-concept study, edoxaban Thrombus Reduction Imaging Study (eTRIS), utilizing an open label design, investigated the efficacy and safety of edoxaban 90 mg once a day for 10 days, followed by edoxaban 60 mg once a day in the treatment of acute, symptomatic DVT (ClinicalTrials.gov Identifier: NCT01662908). eTRIS addresses whether edoxaban monotherapy, without concomitant low molecular weight heparin (LMW heparin) at the time of treatment initiation, is more effective than standard treatment with LMW heparin/warfarin therapy in subjects with DVT, as assessed by the percent (%) change from baseline in thrombus volume/size (measured by MRI) at Day 14-21.
Another goal of eTRIS was to develop and validate a straightforward MR venography (MRV) image acquisition and analysis protocol for the quantification of thrombus volume in DVT. To overcome some challenges faced by current MRV protocols in multicenter settings, we utilized a recently FDA-approved, long-circulating, gadolinium-based blood pool contrast agent (gadofosveset trisodium). Compared to the use of extracellular Gd-based chelates (e.g., Gd-DTPA) for MRV, gadofosveset has a significantly longer circulation time, which allows use of a simpler MR acquisition scheme, without any timing of acquisitions. Gadofosveset trisodium is a blood pool MRI contrast agent that circulates for 2-3 hr after intravenous injection15,16. Its safety profile is similar to those of traditional extravascular extracellular MRI contrast agents17. It allows steady-state imaging of the vasculature over a period of 1 hr. Therefore, no operator dependent timing of image acquisition is required after contrast agent injection. The additional advantage of using this contrast agent is that it is a small molecule (molecular weight 857 Da)18 and can permeate the sides of even a fully occluded thrombus, thereby providing excellent contrast of the DVT from surrounding areas on the MRV and enabling quantitative computation of DVT volumes. Previous studies have established the inter-rater reliability of visualizing veins using the MR Volume Interpolated Breath-hold Examination (VIBE) venography using gadofosveset trisodium19. Here, we use a similar approach in a multicenter clinical trial setting to evaluate deep vein thrombosis and use the volume of DVT measured by MRI as an endpoint. eTRIS provides an ideal platform to evaluate the feasibility and reproducibility of analysis of the MRV imaging approach proposed here, using a long-circulating Gd-based blood pool contrast agent for evaluating DVT volumes. We also evaluate the use of a direct thrombus imaging (DTHI) approach to quantify the extent of fresh DVT prior to the injection of contrast agents.
Two MRI examinations were performed during the course of the study: the first within 36 hr after randomization into the edoxaban monotherapy group or heparin/warfarin group, and the second between 14 to 21 days after randomization. The analyses of all the images were performed by a centralized core laboratory. Volume of fresh thrombus is calculated from a Direct Thrombus Imaging (DTHI) in the legs and lower pelvis before the injection of any contrast agent. The total thrombus volume (fresh and old) is computed from a post contrast magnetic resonance venography (MRV) images of the veins in the legs and lower pelvis.

<table><tbody><tr><td>Ablavar (gadofosveset trisodium)</td><td>Lantheus</td><td></td><td>Contrast Agent</td></tr><tr><td>1.5 T or 3 T Scanners</td><td>GE, Siemens, or Phillips</td><td></td><td>GE (Horizon, Signa, Hdx, 750), Siemens (Symphony, Avanto, Sonata, Trio, Aera) or Philips (Intera, Achieva)</td></tr></tbody></table>

a multicenter mri protocol for the evaluation and quantification of deep vein thrombosis

We evaluated a magnetic resonance venography (MRV) approach with gadofosveset to quantify total thrombus volume changes as the principal criterion for treatment efficacy&#160;in a multicenter randomized study comparing edoxaban monotherapy with a heparin/warfarin regimen for acute, symptomatic lower extremities deep vein thrombosis (DVT) treatment. We also used a direct thrombus imaging approach (DTHI, without the use of a contrast agent) to quantify fresh thrombus. We then sought to evaluate the reproducibility of the analysis methodology and applicability of using 3D magnetic resonance venography and direct thrombus imaging for the quantification of DVT in a multicenter trial setting. From 10 randomly selected subjects participating in the edoxaban Thrombus Reduction Imaging Study (eTRIS), total thrombus volume in the entire lower extremity deep venous system was quantified bilaterally. Subjects were imaged using 3D-T1W gradient echo sequences before (direct thrombus imaging, DTHI) and 5 min after injection of 0.03 mmol/kg of gadofosveset trisodium (magnetic resonance venography, MRV). The margins of the DVT on corresponding axial, curved multi-planar reformatted images were manually delineated by two observers to obtain volumetric measurements of the venous thrombi. MRV was used to compute total DVT volume, whereas DTHI was used to compute volume of fresh thrombus. Intra-class correlation (ICC) and Bland Altman analysis were performed to compare inter and intra-observer variability of the analysis. The ICC for inter and intra-observer variability was excellent (0.99 and 0.98, p &#60;0.001, respectively) with no bias on Bland-Altman analysis for MRV images. For DTHI images, the results were slightly lower (ICC = 0.88 and 0.95 respectively, p &#60;0.001), with bias for inter-observer results on Bland-Altman plots. This study showed feasibility of thrombus volume estimation in DVT using MRV with gadofosveset trisodium, with good intra- and inter-observer reproducibility in a multicenter setting.

For the purpose of the reproducibility assessments, the baseline and follow up scans were pooled and analyzed as separate cases. From the 10 randomly selected subjects (2 visits each), there were 59 vessels with DVT identified using the MRV approach and 29 vessels with fresh thrombus identified by the DTHI. In the subset of these 10 randomly selected subjects analyzed for the reproducibility metrics, no vessels with DVT were deemed to be of un-analyzable quality (defined as subjective scoring 0-2 for both MRV and DTHI images). The average total thrombus volume (sum of volumes of each individual vessel with thrombus identified) measured by MRV with contrast was 3.13 ± 6.23 cm3 for the first analysis of the primary reader.
Assessment of reproducibility:
MRV thrombus volume (total thrombus): The intra- and inter-reader variability by intra-class correlation coefficients was 0.98 and 0.96, respectively. Bland-Altman analysis also showed no bias for both intra- and inter-observer assessments as well (one sample t-test with 0, p = 0.537 and 0.834 respectively).
DTHI thrombus volume (fresh thrombus): The intra- and inter-reader variability by intra-class correlation coefficients was 0.88 and 0.95 respectively. Bland-Altman analysis showed no bias for intra-observer assessments (one sample t-test with 0, p = 0.598). However, there was a significant bias observed for inter-observer variability on Bland-Altman analysis (one sample t-test with 0, p = 0.002). This indicates poorer reproducibility for the volume measured by DTHI compared to the MRV measured volumes. Figure 7 shows the ICC and Bland Altman plots for the intra-reader assessments of variability and Figure 8 shows the same plots for the inter-reader assessments.
<img alt="Intra-reader variability analysis; graphs of volume measurements, linear and Bland-Altman plots." src="/files/ftp_upload/52761/52761fig7.jpg" data-altupdatedat="1747911167000" data-alt="Figure 7"> 
Figure 7: Intra-observer variability analysis. Top panels show (a) ICC and (b) Bland Altman plots for MRV data and bottom panels show (c) ICC and (d) Bland-Altman plots for DTHI data. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52761/52761fig7highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Inter-reader variability analysis; linear regression and Bland-Altman plots for MRV, DTHI data." src="/files/ftp_upload/52761/52761fig8.jpg" data-altupdatedat="1747911167000" data-alt="Figure 8"> 
Figure 8: Inter-observer variability analysis. Top panels show (a) ICC and (b) Bland Altman plots for MRV data and bottom panels show (c) ICC and (d) Bland-Altman plots for DTHI data. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52761/52761fig8highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="DVT progression in MRI scans, pre- and post-treatment comparison, medical imaging analysis." src="/files/ftp_upload/52761/52761fig9.jpg" data-altupdatedat="1747911167000" data-alt="Figure 9"> 
Figure 9: Sample images showing reduction in thrombus size 14-21 days after treatment. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52761/52761fig9highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about A Multicenter MRI Protocol for the Evaluation and Quantification of Deep Vein Thrombosis at JoVE.com

A Multicenter MRI Protocol for the Evaluation and Quantification of Deep Vein Thrombosis

The goal of this study is to use magnetic resonance venography with long-circulating gadolinium-based contrast agent and direct thrombus imaging for quantitative evaluation of DVT volume in a multicenter, clinical trial setting. Inter- and intra-observer variability assessments were conducted, and reproducibility of the protocol was determined.

We evaluated a magnetic resonance venography (MRV) approach with gadofosveset to quantify total thrombus volume changes as the principal criterion for ...

a-multicenter-mri-protocol-for-evaluation-quantification-deep-vein

Nanyang Technological University

Research

JoVE Journal

Medicine

17.1K Views.  Icahn School of Medicine at Mount Sinai. The goal of this study is to use magnetic resonance venography with long-circulating gadolinium-based contrast agent and direct thrombus imaging for quantitative evaluation of DVT volume in a multicenter, clinical trial setting. Inter- and intra-observer variability assessments were conducted, and reproducibility of the protocol was determined.

Video: A Multicenter MRI Protocol for the Evaluation and Quantification of Deep Vein Thrombosis

Stenosis of the Inferior Vena Cava: A Murine Model of Deep Vein Thrombosis

Deep vein thrombosis (DVT) and its devastating complication, pulmonary embolism, are a severe health problem with high mortality. Mechanisms of thrombus formation in veins remain obscure. Lack of mobility (e.g., after surgery or long-haul flights) is one of the main factors leading to DVT. The pathophysiological consequence of the lack of mobility is blood flow stagnation in venous valves. Here, a model is described that mimics such flow disturbance as a thrombosis-driving factor. In this model, partial flow restriction (stenosis) in the inferior vena cava (IVC) is created. Closure of about 90% of the IVC lumen for 48 h results in development of thrombi structurally similar to those in humans. The similarities are: i) most of the thrombus volume is red, i.e., consists of red blood cells and fibrin, ii) presence of a white part (lines of Zahn), iii) non-denuded endothelial monolayer, iv) elevated plasma D-Dimer levels, and v) possibility to prevent thrombosis by low molecular weight heparin. Limitations include variable size of thrombi and the fact that a certain percentage of wild-type mice (0 - 35%) may not produce a thrombus. In addition to visual observation and measurement, thrombi may be visualized by non-invasive technologies, such as ultrasonography, which allows for monitoring the dynamics of thrombus development. At shorter time points (1 - 6 h), intravital microscopy may be applied to directly observe events (e.g., recruitment of cells to the vessel wall) preceding thrombus formation. Use of this method by several teams around the world has made it possible to uncover basic mechanisms of DVT initiation and identify potential targets that might be beneficial for its prevention.

We describe here stenosis in the inferior vena cava as a murine model of deep vein thrombosis. This model recapitulates blood flow restriction, one of the major triggers of venous thrombosis in humans.

Deep vein thrombosis (DVT) and its devastating complication, pulmonary embolism, are a severe health problem with high mortality. Mechanisms of thrombus ...

Immunology and Infection

Combined Near-infrared Fluorescent Imaging and Micro-computed Tomography for Directly Visualizing Cerebral Thromboemboli

Direct thrombus imaging visualizes the root cause of thromboembolic infarction. Being able to image thrombus directly allows far better investigation of stroke than relying on indirect measurements, and will be a potent and robust vascular research tool. We use an optical imaging approach that labels thrombi with a molecular imaging thrombus marker&#160;&#8212; a Cy5.5 near-infrared fluorescent (NIRF) probe that is covalently linked to the fibrin strands of the thrombus by the fibrin-crosslinking enzymatic action of activated coagulation factor XIIIa during the process of clot maturation. A micro-computed tomography (microCT)-based approach uses thrombus-seeking gold nanoparticles (AuNPs) functionalized to target the major component of the clot: fibrin. This paper describes a detailed protocol for the combined in vivo microCT and ex vivo NIRF imaging of thromboemboli in a mouse model of embolic stroke. We show that in vivo microCT and fibrin-targeted glycol-chitosan AuNPs (fib-GC-AuNPs) can be used for visualizing both in situ thrombi and cerebral embolic thrombi. We also describe the use of in vivo microCT-based direct thrombus imaging to serially monitor the therapeutic effects of tissue plasminogen activator-mediated thrombolysis. After the last imaging session, we demonstrate by ex vivo NIRF imaging the extent and the distribution of residual thromboemboli in the brain. Finally, we describe quantitative image analyses of microCT and NIRF imaging data. The combined technique of direct thrombus imaging allows two independent methods of thrombus visualization to be compared: the area of thrombus-related fluorescent signal on ex vivo NIRF imaging vs. the volume of hyperdense microCT thrombi in vivo.

This protocol describes the application of combined near-infrared fluorescent (NIRF) imaging and micro-computed tomography (microCT) for visualizing cerebral thromboemboli. This technique allows the quantification of thrombus burden and evolution. The NIRF imaging technique visualizes fluorescently labeled thrombus in excised brain, while the microCT technique visualizes thrombus inside living animals using gold-nanoparticles.

Direct thrombus imaging visualizes the root cause of thromboembolic infarction. Being able to image thrombus directly allows far better investigation of ...

Deep Vein Thrombosis Induced by Stasis in Mice Monitored by High Frequency Ultrasonography

Venous thrombosis is a common condition affecting 1 - 2% of the population, with an annual incidence of 1 in 500. Venous thrombosis can lead to death through pulmonary embolism or results in the post-thrombotic syndrome, characterized by chronic leg pain, swelling, and ulceration, or in chronic pulmonary hypertension resulting in significant chronic respiratory compromise. This is the most common cardiovascular disease after myocardial infarction and ischemic stroke and is a clinical challenge for all medical disciplines, as it can complicate the course of other disorders such as cancer, systemic disease, surgery, and major trauma.
Experimental models are necessary to study these mechanisms. The stasis model induces consistent thrombus size and a quantifiable amount of thrombus. However, it is necessary to systematically ligate side branches of the inferior vena cava to avoid variability in thrombus sizes and any erroneous data interpretation. We have developed a non-invasive technique to measure thrombus size using ultrasonography. Using this technique, we can assess thrombus development and resolution over time in the same animal. This approach limits the number of mice required for quantification of venous thrombosis consistent with the principle of replacement, reduction, and refinement of animals in research. We have demonstrated that thrombus weight and histological analysis of thrombus size correlate with measurement obtained with ultrasonography. Therefore, the current study describes how to induce deep vein thrombosis in mice using the inferior vena cava stasis model and how to monitor it using high frequency ultrasound.

The present protocol describes the steps to obtain venous thrombosis using a stasis model. In addition, we are using a non-invasive method to measure thrombus formation and resolution over time.

Venous thrombosis is a common condition affecting 1 - 2% of the population, with an annual incidence of 1 in 500. Venous thrombosis can lead to death ...

In Vivo Tracking of Edema Development and Microvascular Pathology in a Model of Experimental Cerebral Malaria Using Magnetic Resonance Imaging

Cerebral malaria is a sign of severe malarial disease and is often a harbinger of death. While aggressive management can be life-saving, the detection of cerebral malaria can be difficult. We present an experimental mouse model of cerebral malaria that shares multiple features of the human disease, including edema and microvascular pathology. Using magnetic resonance imaging (MRI), we can detect and track the blood-brain barrier disruption, edema development, and subsequent brain swelling. We describe multiple MRI techniques that can visualize these pertinent pathological changes. Thus, we show that MRI represents a valuable tool to visualize and track pathological changes, such as edema, brain swelling, and microvascular pathology, in vivo.

In Vivo Tracking of Edema Development and Microvascular Pathology in a Model of Experimental Cerebral Malaria Using Magnetic Resonance Imaging

We describe a mouse model of experimental cerebral malaria and show how inflammatory and microvascular pathology can be tracked in vivo using magnetic resonance imaging.

Cerebral malaria is a sign of severe malarial disease and is often a harbinger of death. While aggressive management can be life-saving, the detection of ...

An In vitro System to Gauge the Thrombolytic Efficacy of Histotripsy and a Lytic Drug

Deep vein thrombosis (DVT) is a global health concern. The primary approach to achieve vessel recanalization for critical obstructions is catheter-directed thrombolytics (CDT). To mitigate caustic side effects and the long treatment time associated with CDT, adjuvant and alternative approaches are under development. One such approach is histotripsy, a focused ultrasound therapy to ablate tissue via bubble cloud nucleation. Pre-clinical studies have demonstrated strong synergy between histotripsy and thrombolytics for clot degradation. This report outlines a benchtop method to assess the efficacy of histotripsy-aided thrombolytic therapy, or lysotripsy.
Clots manufactured from fresh human venous blood were introduced into a flow channel whose dimensions and acousto-mechanical properties mimic an iliofemoral vein. The channel was perfused with plasma and the lytic&#160;recombinant tissue-type plasminogen activator. Bubble clouds were generated in the clot with a focused ultrasound source designed for the treatment of femoral venous clots. Motorized positioners were used to translate the source focus along the clot length. At each insonation location, acoustic emissions from the bubble cloud were passively recorded, and beamformed to generate passive cavitation images. Metrics to gauge treatment efficacy included clot mass loss (overall treatment efficacy), and the concentrations of D-dimer (fibrinolysis) and hemoglobin (hemolysis) in the perfusate. There are limitations to this in vitro design, including lack of means to assess in vivo side effects or dynamic changes in flow rate as the clot lyses. Overall, the setup provides an effective method to assess the efficacy of histotripsy-based strategies to treat DVT.

Histotripsy-aided lytic delivery or lysotripsy is under development for the treatment of deep vein thrombosis. An in vitro procedure is presented here to assess the efficacy of this combination therapy. Key protocols for the clot model, image guidance, and assessment of treatment efficacy are discussed.

Deep vein thrombosis (DVT) is a global health concern. The primary approach to achieve vessel recanalization for critical obstructions is ...

Bioengineering

Quantitative MRI of Endothelial Permeability and (Dys)function in Atherosclerosis

Cardiovascular diseases are the leading causes of death worldwide. A permeable/leaky and dysfunctional endothelium is considered the earliest marker of vascular damage and thought to drive atherosclerosis. A method to identify these changes in vivo would be desirable in the clinic. Magnetic resonance imaging (MRI)-based tools and other technologies have enabled a profound understanding of the role of the endothelium in cardiovascular diseases and risk in vivo. There is, however, a need for reproducible and simple approaches for extracting quantifiable data reflective of endothelial damage from a single imaging study. A non-invasive, easy-to-implement, and quantitative MRI workflow was developed to acquire and analyze images that allow the quantification of two imaging biomarkers of arterial endothelial damage (leakiness/permeability and dysfunction). Here, the protocol describes the application of this method in the brachiocephalic artery of atherosclerotic ApoE-/- mice using a clinical MRI scanner. First, late gadolinium enhancement (LGE) and Modified Look-Locker Inversion Recovery (MOLLI) T1 mapping protocols to quantify endothelial leakage using an albumin-binding probe are described. Second, anatomic, and quantitative blood flow sequences to measure endothelial dysfunction, in response to acetylcholine are described. Importantly, the method outlined here allows the acquisition of high-spatial-resolution 3D images with large volumetric coverage enabling accurate segmentation of vessel wall structures to improve inter- and intra-observer variability and to increase reliability and reproducibility. Additionally, it provides quantitative data without the need for high-temporal resolution for complex kinetic modeling, making it model-independent and even allowing for imaging of highly mobile vessels (coronary arteries). Therefore, the approach simplifies and expedites data analysis. Finally, this method can be implemented on different scanners, can be extended to image different arterial beds, and is clinically applicable for use in humans. This method could be used to diagnose and treat patients with atherosclerosis by adopting a precision-medicine approach.

Quantitative MRI of Endothelial Permeability and Dysfunction in Atherosclerosis

We have developed an accurate, non-invasive, and easy-to-use method to quantify endothelial permeability and dysfunction in the arteries using Magnetic Resonance Imaging (MRI), named qMETRIC. This technique enables assessing vascular damage and cardiovascular risk associated with atherosclerosis in preclinical models and humans.

Cardiovascular diseases are the leading causes of death worldwide. A permeable/leaky and dysfunctional endothelium is considered the earliest marker of ...

Cardiac Magnetic Resonance for the Evaluation of Suspected Cardiac Thrombus: Conventional and Emerging Techniques

We present the conventional cardiac magnetic resonance (CMR) protocol for evaluating a suspected thrombus and highlight emerging techniques.&#160;The appearance of a mass on certain magnetic resonance (MR) sequences can help differentiate a thrombus from competing diagnoses such as a tumor. T1 and T2 signal characteristics of a thrombus are related to the evolution of hemoglobin properties. A thrombus typically does not enhance following contrast administration, which also helps differentiation from a tumor. We also highlight the emerging role of T1 mapping in the evaluation of a thrombus, which can add another level of support in diagnosis. Prior to any CMR exam, patient screening and interviews are critical to ensure safety and to optimize patient comfort. Effective communication during the exam between the technologist and the patient promotes proper breath holding technique and higher quality images. Volumetric post processing and structured reporting are helpful to ensure that the radiologist answers the ordering services&#39; question and communicates these results effectively. Optimal pre-MR safety evaluation, CMR exam execution, and post exam processing and reporting allow for delivery of high quality radiological service in the evaluation of a suspected cardiac thrombus.

The goal of this article is to describe how cardiac magnetic resonance can be used for the evaluation and diagnosis of a suspected cardiac thrombus. The method presented will describe data acquisition as well as the pre-procedure and post-procedure protocol.

We present the conventional cardiac magnetic resonance (CMR) protocol for evaluating a suspected thrombus and highlight emerging techniques.&#160;The ...

Image Acquisition Method for the Sonographic Assessment of the Inferior Vena Cava

Over the past several decades, clinicians have incorporated several applications of diagnostic point-of-care ultrasound (POCUS) into medical decision-making. Among the applications of POCUS, imaging the inferior vena cava (IVC) is practiced by a wide variety of specialties, such as nephrology, emergency medicine, internal medicine, critical care, anesthesiology, pulmonology, and cardiology. Although each specialty uses IVC data in slightly different ways, most medical specialties, at minimum, attempt to use IVC data to make predictions about intravascular volume status. While the relationship between IVC sonographic data and intravascular volume status is complex and highly context-dependent, all clinicians should collect the sonographic data in standardized ways to ensure repeatability. This paper describes standardized IVC image acquisition including patient positioning, transducer selection, probe placement, image optimization, and the pitfalls and limitations of IVC sonographic imaging.&#160;This paper also describes the commonly performed anterior IVC long-axis view and three other views of the IVC that can each provide helpful diagnostic information when the anterior long-axis view is difficult to obtain or interpret.

Point-of-care ultrasound evaluation of the inferior vena cava (IVC) is commonly utilized to identify, among other things, the volume status. Imaging should be performed systematically to ensure repeatability. This manuscript reviews the methods and pitfalls of sonographic IVC examination.

Over the past several decades, clinicians have incorporated several applications of diagnostic point-of-care ultrasound (POCUS) into medical ...

Point-Of-Care Ultrasound Screening for Proximal Lower Extremity Deep Venous Thrombosis

Acute lower extremity deep venous thrombosis (DVT) is a serious vascular disorder that requires accurate and early diagnosis to prevent life-threatening sequelae. While whole leg compression ultrasound with color and spectral Doppler is commonly performed in radiology and vascular labs, point-of-care ultrasound (POCUS) is becoming more common in the acute care setting. Providers appropriately trained in focused POCUS can perform a rapid bedside examination with high sensitivity and specificity in critically ill patients. This paper describes a simplified yet validated approach to POCUS by describing a three-zone protocol for lower extremity DVT POCUS image acquisition. The protocol explains the steps in obtaining vascular images at six compression points in the lower extremity. Beginning at the level of the proximal thigh and moving distally to the popliteal space, the protocol guides the user through each of the compression points in a stepwise manner: from the common femoral vein to the femoral and deep femoral vein bifurcation, and, finally, to the popliteal vein. Further, a visual aid is provided that may assist providers during real-time image acquisition. The goal in presenting this protocol is to help make proximal lower extremity DVT exams more accessible and efficient for POCUS users at the patient&#39;s bedside.

Traditionally, lower extremity deep venous thrombosis (DVT) is diagnosed by radiology-performed venous duplex ultrasound. Providers appropriately trained in focused point-of-care ultrasound (POCUS) can perform a rapid bedside examination with high sensitivity and specificity in critically ill patients. We describe the scanning technique for focused POCUS DVT lower extremity examination.

Acute lower extremity deep venous thrombosis (DVT) is a serious vascular disorder that requires accurate and early diagnosis to prevent life-threatening ...

Demystifying Venous Excess Ultrasound (VExUS): Image Acquisition and Interpretation

Providers in many medical specialties must accurately assess the hemodynamic circuit to deliver appropriate patient care. Venous congestion is increasingly implicated in a range of multiorgan complications. However, hemodynamic assessment remains challenging because of the complex physiology involved and inconsistent diagnostic accuracy of conventional bedside tools and physical exam maneuvers. While right heart catheterization is regarded as the gold standard for measuring systemic venous pressure, it is invasive and not easily repeatable, and thus, there remains a need for non-invasive alternatives. Even point-of-care ultrasound examinations of the internal jugular vein or inferior vena cava have significant limitations in terms of accuracy of intravascular volume assessment and correlation with central venous pressure. To improve bedside clinicians' accuracy at assessing venous congestion, a protocol was developed and validated that utilizes pulsed-wave (PW) Doppler signals of veins in the liver and kidney to grade the degree of venous congestion present in patients. Although this scoring system, called Venous Excess Ultrasound (VExUS), is being increasingly adopted within certain subspecialties of medicine, such as nephrology and critical care, it remains underutilized in medicine as a whole. This is likely due, at least in part, to knowledge gaps and lack of training in this emerging modality. To address this educational gap, this article will describe VExUS image acquisition and interpretation.

Point-of-care ultrasound (POCUS) is often used to assess the hemodynamic circuit and detect the presence of venous congestion. The Venous Excess Ultrasound (VExUS) scoring system was developed to aid clinicians in predicting the impact of venous congestion on organ dysfunction. This article aims to describe VExUS image acquisition and interpretation.

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Demystifying Venous Excess Ultrasound (VExUS): Image Acquisition and Interpretation