3D T(1)-mapping for the characterization of deep vein thrombosis

Circle or semi-circle hyper-intensity on T1 high-resolution isovolumetric examination (THRIVE) indicates the young age of experimentally induced caval thrombus

To evaluate the age of caval thrombus that experimentally induced in swine by use of magnetic resonance imaging (MRI). Caval thrombus was experimentally created in 15 swine by autologous clot injection assisted with caval net knitting. Serial high-resolution MR images were obtained using magnetic resonance venography (MRV) and T1 high-resolution isotropic volume examination (THRIVE) sequences in a 3.0-T MR system at 1, 7, 14, 21, and 28 days post model creation. At each time point, three pigs were sacrificed and the thrombotic vena cava was processed for histopathological examinations respectively. Caval thrombus was successfully induced in 15 pigs in group A. The signal intensity (SI) change of caval thrombus on THRIVE was age-dependent, with a typical sign of circle or semi-circle hyper-intensity at 7-day-old model while SI of thrombus was lower than that of muscle from day 14 throughout day 28. The histo-pathological findings revealed that RBCs-rich thrombus at day 1 without blue-stained particles, RBCs layers with infiltration of inflammatory cells and sporadically distributed blue-stained particles at 7-day-old thrombus. At day 14, 21 and 28, blue-stained particles became richer, coupled with formation of granulation tissue and fibrous tissue. The swine model in the study is good for age evaluation of venous thrombosis. The peripheral circle or semi-circle hyperintensity on THRIVE indicates the young age of caval thrombus in swine.

ACR Appropriateness Criteria® Suspected Upper Extremity Deep Vein Thrombosis

This publication includes the appropriate imaging modalities to assess suspected deep vein thrombosis in the upper extremities. Ultrasound duplex Doppler is the most appropriate imaging modality to assess upper-extremity deep vein thrombosis. It is a noninvasive test, which can be performed at the bedside and used for serial evaluations. Ultrasound can also directly identify thrombus by visualizing echogenic material in the vein and by lack of compression of the vein walls from manual external pressure. It can indirectly identify thrombus from altered blood-flow patterns. It is most appropriate in the evaluation of veins peripheral to the brachiocephalic vein. CT venography and MR venography are not first-line imaging tests, but are appropriate to assess the central venous structures, or to assess the full range of venous structures from the hand to the right atrium. Catheter venography is appropriate if therapy is required. Radionuclide venography and chest radiography are usually not appropriate to assess upper-extremity deep vein thrombosis. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Diagnosing Recurrent DVT of the Leg by Two Different Non-Contrast-Enhanced Magnetic Resonance Direct Thrombus Imaging Techniques: A Pilot Study

Introduction  Magnetic resonance direct thrombus imaging (MRDTI) is a promising technique to improve the diagnostic management of patients with a suspected ipsilateral recurrent deep vein thrombosis (DVT) by direct visualization of a thrombus. Another magnetic resonance imaging (MRI) technique, T1-weighted turbo spin-echo spectral attenuated inversion recovery (TSE-SPAIR), has the potential to image a thrombus directly with a high spatial resolution as well. The main aim of this pilot study was to investigate if adding the TSE-SPAIR sequence to an MRDTI sequence performed in patients with suspected recurrent DVT may increase the diagnostic confidence of expert MRDTI readers.

Methods  Fifteen patients with suspected acute recurrent DVT were included in this study. The TSE-SPAIR sequence was scanned directly after the MRDTI scan but not used to guide clinical decision making, and both scans were adjudicated post hoc two times separately by three independent expert MRDTI readers. Diagnostic confidence was scored on a 4-point Likert scale: (1) poor (definite diagnosis impossible), (2) fair (evaluation of major findings possible), (3) good (definite diagnosis possible), and (4) excellent (exact diagnosis possible).

Results  The diagnostic confidence of expert readers increased when adding the TSE-SPAIR sequence on top of the MRDTI sequence from “good” (median, 3.0; interquartile range [IQR], 2.66–3.0) to “excellent” (median, 3.67; IQR 3.33–3.67; p  = 0.001). Evaluation of the scans in the reversed order 5 months after initial reading showed similar results. Diagnostic accuracy for proximal DVT of both scan techniques was good.

Conclusion  The extra TSE-SPAIR sequence may help increase diagnostic confidence of radiologists in cases of uncertain diagnosis in patients with suspected ipsilateral recurrent DVT.

Use of Computed Tomography and Magnetic Resonance Imaging in Central Venous Disease

Successful management of acute deep vein thrombosis and post-thrombotic syndrome depends on careful patient selection and detailed investigation of thrombus extent, composition, and anatomy. This article reviews the use of computerized tomography and magnetic resonance imaging in the assessment of central deep veins of the pelvis and addresses new developments within the field. Despite drawbacks of each imaging modality, when contemplating deep venous reconstruction, cross-sectional imaging should be considered for preoperative planning and to compliment intraoperative imaging tools, including intravascular ultrasound and contrast venography.

Cardiovascular magnetic resonance black-blood thrombus imaging for the diagnosis of acute deep vein thrombosis at 1.5 Tesla

BACKGROUND

The aim was to investigate the feasibility of a cardiovascular magnetic resonance (CMR) black-blood thrombus imaging (BBTI) technique, based on delay alternating with nutation for tailored excitation black-blood preparation and a variable flip angle turbo-spin-echo readout, for the diagnosis of acute deep vein thrombosis (DVT) at 1.5 T.

METHODS

BBTI was conducted in 15 healthy subjects and 30 acute DVT patients. Contrast-enhanced CMR venography (CE-CMRV) was conducted for comparison and only performed in the patients. Apparent contrast-to-noise ratios between the thrombus and the muscle/lumen were calculated to determine whether BBTI could provide an adequate thrombus signal for diagnosis. Two blinded readers assessed the randomized BBTI images from all participants and made independent decisions on the presence or absence of thrombus at the segment level. Images obtained by CE-CMRV were also randomized and assessed by the two readers. Using the consensus CE-CMRV as a reference, the sensitivity, specificity, positive and negative predictive values, and accuracy of BBTI, as well as its diagnostic agreement with CE-CMRV, were calculated. Additionally, diagnostic confidence and interobserver diagnostic agreement were evaluated.

RESULTS

The thrombi in the acute phase exhibited iso- or hyperintense signals on the BBTI images. All the healthy subjects were correctly identified from the participants based on the segment level. The diagnostic confidence of BBTI was comparable to that of CE-CMRV (3.69 ± 0.52 vs. 3.70 ± 0.47). High overall sensitivity (95.2%), SP (98.6%), positive predictive value (96.0%), negative predictive value (98.3%), and accuracy (97.7%), as well as excellent diagnostic and interobserver agreements, were achieved using BBTI.

CONCLUSION

BBTI is a reliable, contrast-free technique for the diagnosis of acute DVT at 1.5 T.

Black-blood thrombus imaging (BTI): a contrast-free cardiovascular magnetic resonance approach for the diagnosis of non-acute deep vein thrombosis

BACKGROUND

Deep vein thrombosis (DVT) is a common but elusive illness that can result in long-term disability or death. Accurate detection of thrombosis and assessment of its size and distribution are critical for treatment decision-making. In the present study, we sought to develop and evaluate a cardiovascular magnetic resonance (CMR) black-blood thrombus imaging (BTI) technique, based on delay alternating with nutation for tailored excitation black-blood preparation and variable flip angle turbo-spin-echo readout, for the diagnosis of non-acute DVT. METHODS: This prospective study was approved by institutional review board and informed consent obtained from all subjects. BTI was first conducted in 11 healthy subjects for parameter optimization and then conducted in 18 non-acute DVT patients to evaluate its diagnostic performance. Two clinically used CMR techniques, contrast-enhanced CMR venography (CE-MRV) and three dimensional magnetization prepared rapid acquisition gradient echo (MPRAGE), were also conducted in all patients for comparison. All images obtained from patients were analyzed on a per-segment basis. Using the consensus diagnosis of CE-MRV as the reference, the sensitivity (SE), specificity (SP), positive and negative predictive values (PPV and NPV), and accuracy (ACC) of BTI and MPRAGE as well as their diagnostic agreement with CE-MRV were calculated. Besides, diagnostic confidence and interreader diagnostic agreement were evaluated for all three techniques.

RESULTS

BTI with optimized parameters effectively nulled the venous blood flow signal and allowed directly visualizing the thrombus within the black-blood lumen. Higher SE (90.4% vs 67.6%), SP (99.0% vs. 97.4%), PPV (95.4% vs. 85.6%), NPV (97.8% vs 92.9%) and ACC (97.4% vs. 91.8%) were obtained by BTI in comparison with MPRAGE. Good diagnostic confidence and excellent diagnostic and interreader agreements were achieved by BTI, which were superior to MPRAGE on detecting the chronic thrombus.

CONCLUSION

BTI allows direct visualization of non-acute DVT within the dark venous lumen and has the potential to be a reliable diagnostic tool without the use of contrast medium.

Increased Vascular Permeability Measured With an Albumin-Binding Magnetic Resonance Contrast Agent Is a Surrogate Marker of Rupture-Prone Atherosclerotic Plaque

BACKGROUND

Compromised structural integrity of the endothelium and higher microvessel density increase vascular permeability. We investigated whether vascular permeability measured in vivo by magnetic resonance imaging using the albumin-binding contrast agent, gadofosveset, is a surrogate marker of rupture-prone atherosclerotic plaque in a rabbit model.

METHODS AND RESULTS

New Zealand white rabbits (n=10) were rendered atherosclerotic by cholesterol-diet and endothelial denudation. Plaque rupture was triggered with Russell's viper venom and histamine. Animals were imaged pre-triggering, at 3 and 12 weeks, to quantify plaque area, vascular permeability, vasodilation, and stiffness and post-triggering to identify thrombus. Plaques identified on the pretrigger scans were classified as stable or rupture-prone based on the absence or presence of thrombus on the corresponding post-trigger magnetic resonance imaging, respectively. All rabbits had developed atherosclerosis, and 60% had ruptured plaques. Rupture-prone plaques had higher vessel wall relaxation rate (R1; 2.30±0.5 versus 1.86±0.3 s-1; P<0.001), measured 30 minutes after gadofosveset administration, and higher R1/plaque area ratio (0.70±0.06 versus 0.47±0.02, P= 0.01) compared with stable plaque at 12 weeks. Rupture-prone plaques had higher percent change in R1 between the 3 and 12 weeks compared with stable plaque (50.80±7.2% versus 14.22±2.2%; P<0.001). Immunohistochemistry revealed increased vessel wall albumin and microvessel density in diseased aortas and especially in ruptured plaque. Electron microscopy showed lack of structural integrity in both luminal and microvascular endothelium in diseased vessels. Functionally, the intrinsic vasodilation of the vessel wall decreased at 12 weeks compared with 3 weeks (18.60±1.0% versus 23.43±0.8%; P<0.001) and in rupture-prone compared with stable lesions (16.40±2.0% versus 21.63±1.2%; P<0.001). Arterial stiffness increased at 12 weeks compared with 3 weeks (5.00±0.1 versus 2.53±0.2 m/s; P<0.001) both in animals with stable and rupture-prone lesions.

CONCLUSIONS

T1 mapping using an albumin-binding contrast agent (gadofosveset) could quantify the changes in vascular permeability associated with atherosclerosis progression and rupture-prone plaques.

Synthesis, Characterization, and Application of Core-Shell Co0.16Fe2.84O4@NaYF4(Yb, Er) and Fe3O4@NaYF4(Yb, Tm) Nanoparticle as Trimodal (MRI, PET/SPECT, and Optical) Imaging Agents

Multimodal nanoparticulate materials are described, offering magnetic, radionuclide, and fluorescent imaging capabilities to exploit the complementary advantages of magnetic resonance imaging (MRI), positron emission tomography/single-photon emission commuted tomography (PET/SPECT), and optical imaging. They comprise Fe3O4@NaYF4 core/shell nanoparticles (NPs) with different cation dopants in the shell or core, including Co0.16Fe2.84O4@NaYF4(Yb, Er) and Fe3O4@NaYF4(Yb, Tm). These NPs are stabilized by bisphosphonate polyethylene glycol conjugates (BP-PEG), and then show a high transverse relaxivity (r2) up to 326 mM(-1) s(-1) at 3T, a high affinity to [(18)F]-fluoride or radiometal-bisphosphonate conjugates (e.g., (64)Cu and (99m)Tc), and fluorescent emissions from 500 to 800 nm under excitation at 980 nm. The biodistribution of intravenously administered particles determined by PET/MR imaging suggests that negatively charged Co0.16Fe2.84O4@NaYF4(Yb, Er)-BP-PEG (10K) NPs cleared from the blood pool more slowly than positively charged NPs Fe3O4@NaYF4(Yb, Tm)-BP-PEG (2K). Preliminary results in sentinel lymph node imaging in mice indicate the advantages of multimodal imaging.

Assessment of Venous Thrombosis in Animal Models

Deep vein thrombosis and common complications, including pulmonary embolism and post-thrombotic syndrome, represent a major source of morbidity and mortality worldwide. Experimental models of venous thrombosis have provided considerable insight into the cellular and molecular mechanisms that regulate thrombus formation and subsequent resolution. Here, we critically appraise the ex vivo and in vivo techniques used to assess venous thrombosis in these models. Particular attention is paid to imaging modalities, including magnetic resonance imaging, micro-computed tomography, and high-frequency ultrasound that facilitate longitudinal assessment of thrombus size and composition.

PET/CT and MR imaging biomarker of lipid-rich plaques using [64Cu]-labeled scavenger receptor (CD68-Fc)

Continued uptake of modified low-density lipoproteins (LDL) by the scavenger receptor, CD68, of activated macrophages is a crucial process in the development of atherosclerotic plaques and leads to the formation of foam cells. Eight-weeks-old male Apolipoprotein E-deficient (ApoE(-/-)) mice (n = 6) were fed a high-fat diet for 12 weeks. C57BL/6J wildtype (WT) mice served as controls (n = 6). Positron emission tomography (PET) with an acquisition time of 1800 s (NanoPET/CT scanner; Mediso, Hungary & Bioscan, USA) was carried out 24h after intravenous tail vein administration of 50 µl (64)Cu-CD68-Fc (~20-30 µg labeled protein/mouse containing approximately 10-12 MBq (64)Cu-CD68-Fc per mouse). Three days after PET/CT, all mice received an intravenous administration of 0.2 mmol/kg body weight of a gadolinium-based elastin-binding contrast agent to assess plaque burden and vessel wall remodeling. Two hours after injection, mice were imaged in a 3T clinical MR scanner (Philips Healthcare, Best, NL) using a dedicated single loop surface coil (23 mm). Enhanced (64)Cu-CD68-Fc uptake was found in the aortic arches of ApoE(-/-) compared to WT mice (ApoE(-/-) mice:10.5 ± 1.5 Bq/cm(3) vs. WT mice: 2.1 ± 0.3 Bq/cm(3); P = 0.002). Higher gadolinium-based elastin-binding contrast agent uptake was also detected in the aortic arch of ApoE(-/-) compared to WT mice using R(1) maps (R(1) = 1.47 ± 0.06 s(-1) vs. 0.92 ± 0.05 s(-1); P <0.001). Radiolabeled scavenger receptor ((64)Cu-CD68-Fc) may help to target foam cell rich plaques with high content of oxidized LDL. This novel imaging biomarker tool may have potential to identify unstable plaques and for risk stratification.

Aluminium hydroxide stabilised MnFe2O4 and Fe3O4 nanoparticles as dual-modality contrasts agent for MRI and PET imaging

Magnetic nanoparticles (NPs) MnFe2O4 and Fe3O4 were stabilised by depositing an Al(OH)3 layer via a hydrolysis process. The particles displayed excellent colloidal stability in water and a high affinity to [(18)F]-fluoride and bisphosphonate groups. A high radiolabeling efficiency, 97% for (18)F-fluoride and 100% for (64)Cu-bisphosphonate conjugate, was achieved by simply incubating NPs with radioactivity solution at room temperature for 5 min. The properties of particles were strongly dependant on the thickness and hardness of the Al(OH)3 layer which could in turn be controlled by the hydrolysis method. The application of these Al(OH)3 coated magnetic NPs in molecular imaging has been further explored. The results demonstrated that these NPs are potential candidates as dual modal probes for MR and PET. In vivo PET imaging showed a slow release of (18)F from NPs, but no sign of efflux of (64)Cu.

Fibrin-targeted magnetic resonance imaging allows in vivo quantification of thrombus fibrin content and identifies thrombi amenable for thrombolysis

OBJECTIVE

Deep venous thrombosis is a major health problem. Thrombolytic therapies are effective in recanalizing the veins and preventing post-thrombotic complications, but there is no consensus on selection criteria. The aim of this study was to investigate a fibrin-specific MRI contrast agent (EP-2104R) for the accurate quantification of thrombus' fibrin content in vivo and for the identification of thrombus suitable for thrombolysis.

APPROACH AND RESULTS

Venous thrombosis was induced in the inferior vena cava of 8- to 10-week-old male BALB/C mice and MRI performed 2, 4, 7, 10, 14, and 21 days later. Eighteen mice were scanned at each time point pre and 2 hours post injection of EP-2104R (8.0 μmol/kg) with 12 mice at each time point used to correlate fibrin contrast uptake with thrombus' histological stage and fibrin content. Six mice at each time point were immediately subjected to intravascular thrombolytic therapy (10 mg/kg of tissue-type plasminogen activator). Mice were imaged to assess response to lytic therapy 24 hours after thrombolytic treatment. Two mice at each time point were scanned post injection of 0.2 mmol/kg of Gd-DTPA (gadolinium with diethylenetriaminepentacetate, Magnevist, Schering AG, Berlin, Germany) for control purpose. Contrast uptake was correlated positively with the fibrin content of the thrombus measured by Western blotting (R(2)=0.889; P<0.001). Thrombus relaxation rate (R1) post contrast and the change in visualized thrombus size on late gadolinium enhancement inversion recovery MRI pre-EP-2104R and post-EP-2104R injection were the best predictors for successful thrombolysis (area under the curve, 0.989 [95% confidence interval, 0.97-1.00] and 0.994 [95% confidence interval, 0.98-1.00] respectively).

CONCLUSIONS

MRI with a fibrin-specific contrast agent accurately estimates thrombus fibrin content in vivo and identifies thrombi that are amenable for thrombolysis.

Molecular MRI of atherosclerosis

Despite advances in prevention, risk assessment and treatment, coronary artery disease (CAD) remains the leading cause of morbidity and mortality in Western countries. The lion's share is due to acute coronary syndromes (ACS), which are predominantly triggered by plaque rupture or erosion and subsequent coronary thrombosis. As the majority of vulnerable plaques does not cause a significant stenosis, due to expansive remodeling, and are rather defined by their composition and biological activity, detection of vulnerable plaques with x-ray angiography has shown little success. Non-invasive vulnerable plaque detection by identifying biological features that have been associated with plaque progression, destabilization and rupture may therefore be more appropriate and may allow earlier detection, more aggressive treatment and monitoring of treatment response. MR molecular imaging with target specific molecular probes has shown great promise for the noninvasive in vivo visualization of biological processes at the molecular and cellular level in animals and humans. Compared to other imaging modalities; MRI can provide excellent spatial resolution; high soft tissue contrast and has the ability to simultaneously image anatomy; function as well as biological tissue composition and activity.

Positron emission tomography/computed tomographic and magnetic resonance imaging in a murine model of progressive atherosclerosis using (64)Cu-labeled glycoprotein VI-Fc

BACKGROUND

Plaque erosion leads to exposure of subendothelial collagen, which may be targeted by glycoprotein VI (GPVI). We aimed to detect plaque erosion using (64)Cu-labeled GPVI-Fc (fragment crystallized).

METHODS AND RESULTS

Four-week-old male apolipoprotein E-deficient (ApoE(-/-)) mice (n=6) were fed a high-fat diet for 12 weeks. C57BL/6J wild-type (WT) mice served as controls (n=6). Another group of WT mice received a ligation injury of the left carotid artery (n=6) or sham procedure (n=4). All mice received a total activity of ≈12 MBq (64)Cu-GPVI-Fc by tail vein injection followed by delayed (24 hours) positron emission tomography using a NanoPET/computed tomographic scanner (Mediso, Hungary; Bioscan, USA) with an acquisition time of 1800 seconds. Seventy-two hours after positron emission tomography/computed tomography, all mice were scanned 2 hours after intravenous administration of 0.2 mmol/kg body weight of a gadolinium-based elastin-specific MR contrast agent. MRI was performed on a 3-T clinical scanner (Philips Healthcare, Best, The Netherlands). In ApoE(-/-) mice, the (64)Cu-GPVI-Fc uptake in the aortic arch was significantly higher compared with WT mice (ApoE(-/-): 13.2±1.5 Bq/cm(3) versus WT mice: 5.1±0.5 Bq/cm(3); P=0.028). (64)Cu-GPVI-Fc uptake was also higher in the injured left carotid artery wall compared with the intact right carotid artery of WT mice and as a trend compared with sham procedure (injured: 20.7±1.3 Bq/cm(3) versus intact: 2.3±0.5 Bq/cm(3); P=0.028 versus sham: 12.7±1.7 Bq/cm(3); P=0.068). Results were confirmed by ex vivo histology and in vivo MRI with elastin-specific MR contrast agent that measures plaque burden and vessel wall remodeling. Higher R1 relaxation rates were found in the injured carotid wall with a T1 mapping sequence (injured: 1.44±0.08 s(-1) versus intact: 0.91±0.02 s(-1); P=0.028 versus sham: 0.97±0.05 s(-1); P=0.068) and in the aortic arch of ApoE(-/-) mice compared with WT mice (ApoE(-/-): 1.49±0.05 s(-1) versus WT: 0.92±0.04 s(-1); P=0.028).

CONCLUSIONS

(64)Cu-GPVI-Fc positron emission tomographic imaging allows identification of exposed subendothelial collagen in injured WT and high-fat diet-fed ApoE(-/-) mice.

Noninvasive MRI monitoring of the effect of interventions on endothelial permeability in murine atherosclerosis using an albumin-binding contrast agent

Background

Endothelial dysfunction promotes atherosclerosis. We investigated whether in vivo magnetic resonance imaging (MRI) using an albumin‐binding contrast agent, gadofosveset, could monitor the efficacy of minocycline and ebselen in reducing endothelial permeability and atherosclerotic burden in the brachiocephalic artery of high‐fat diet (HFD)–fed ApoE^−/− mice.

Methods and Results

ApoE^−/− mice were scanned 12 weeks after commencement of either a normal diet (controls) or an HFD. HFD‐fed ApoE^−/− mice were either untreated or treated with minocycline or ebselen for 12 weeks. Delayed‐enhancement MRI and T₁ mapping of the brachiocephalic artery, 30 minutes after injection of gadofosveset, showed increased vessel wall enhancement and relaxation rate (R₁, s⁻¹) in untreated HFD‐fed ApoE^−/− mice (R₁=3.8±0.52 s⁻¹) compared with controls (R₁=2.15±0.34 s⁻¹, P<0.001). Conversely, minocycline‐treated (R₁=2.7±0.17 s⁻¹, P<0.001) and ebselen‐treated (R₁=2.7±0.23 s⁻¹, P<0.001) ApoE^−/− mice showed less vessel wall enhancement compared with untreated HFD‐fed ApoE^−/− mice. Mass spectroscopy showed a lower gadolinium concentration in the brachiocephalic artery of treated (minocycline=28.5±3 μmol/L, ebselen=32.4±4 μmol/L) compared with untreated HFD‐fed ApoE^−/− mice (191±4.8 μmol/L) (P<0.02). Both interventions resulted in a lower plaque burden as measured by delayed‐enhancement MRI (minocycline=0.14±0.02 mm², ebselen=0.20±0.09 mm², untreated=0.44±0.01 mm²; P<0.001) and histology (minocycline=0.13±0.05 mm², ebselen=0.18±0.02 mm², untreated=0.32±0.04 mm²; P<0.002). Endothelium cells displayed fewer structural changes and smaller gap junction width in treated compared with untreated animals as seen by electron microscopy (minocycline=42.3±8.4 nm, ebselen=56.5±17 nm, untreated=2400±39 nm; P<0.001). Tissue flow cytometry of the brachiocephalic artery showed lower monocyte/macrophage content in both ebselen‐ and minocycline‐treated mice (8.06±3.2% and 7.62±1.73%, respectively) compared with untreated animals (20.1±2.2%) (P=0.03), with significant attenuation of the proinflammatory Ly6C^high subtype (untreated mice, 42.64±6.1% of total monocytes; ebselen, 14.07±9.5% of total monocytes; minocycline, 26.42±0.6% of total monocytes).

Conclusions

We demonstrate that contrast‐enhanced MRI with an albumin‐binding contrast agent can be used to noninvasively monitor the effect of interventions on endothelial permeability and plaque burden. Blood albumin leakage could be a surrogate marker for the in vivo evaluation of interventions that aim at restoring endothelial integrity.

Magnetic resonance T1 relaxation time of venous thrombus is determined by iron processing and predicts susceptibility to lysis

BACKGROUND

The magnetic resonance longitudinal relaxation time (T1) changes with thrombus age in humans. In this study, we investigate the possible mechanisms that give rise to the T1 signal in venous thrombi and whether changes in T1 relaxation time are informative of the susceptibility to lysis.

METHODS AND RESULTS

Venous thrombosis was induced in the vena cava of BALB/C mice, and temporal changes in T1 relaxation time correlated with thrombus composition. The mean T1 relaxation time of thrombus was shortest at 7 days following thrombus induction and returned to that of blood as the thrombus resolved. T1 relaxation time was related to thrombus methemoglobin formation and further processing. Studies in inducible nitric oxide synthase (iNOS(-/-))-deficient mice revealed that inducible nitric oxide synthase mediates oxidation of erythrocyte lysis-derived iron to paramagnetic Fe3+, which causes thrombus T1 relaxation time shortening. Studies using chemokine receptor-2-deficient mice (Ccr2(-/-)) revealed that the return of the T1 signal to that of blood is regulated by removal of Fe3+ by macrophages that accumulate in the thrombus during its resolution. Quantification of T1 relaxation time was a good predictor of successful thrombolysis with a cutoff point of <747 ms having a sensitivity and specificity to predict successful lysis of 83% and 94%, respectively.

CONCLUSIONS

The source of the T1 signal in the thrombus results from the oxidation of iron (released from the lysis of trapped erythrocytes in the thrombus) to its paramagnetic Fe3+ form. Quantification of T1 relaxation time appears to be a good predictor of the success of thrombolysis.

In vivo magnetization transfer and diffusion-weighted magnetic resonance imaging detects thrombus composition in a mouse model of deep vein thrombosis

BACKGROUND

Deep vein thrombosis remains a major health problem necessitating accurate diagnosis. Thrombolysis is associated with significant morbidity and is effective only for the treatment of unorganized thrombus. We tested the feasibility of in vivo magnetization transfer (MT) and diffusion-weighted magnetic resonance imaging to detect thrombus organization in a murine model of deep vein thrombosis.

METHODS AND RESULTS

Deep vein thrombosis was induced in the inferior vena cava of male BALB/C mice. Magnetic resonance imaging was performed at days 1, 7, 14, 21, and 28 after thrombus induction using MT, diffusion-weighted, inversion-recovery, and T1-mapping protocols. Delayed enhancement and T1 mapping were repeated 2 hours after injection of a fibrin contrast agent. Finally, excised thrombi were used for histology. We found that MT and diffusion-weighted imaging can detect histological changes associated with thrombus aging. MT rate (MTR) maps and percentage of MT rate (%MTR) allowed visualization and quantification of the thrombus protein content, respectively. The %MTR increased with thrombus organization and was significantly higher at days 14, 21, and 28 after thrombus induction (days 1, 7, 14, 21, 28: %MTR=2483±451, 2079±1210, 7029±2490, 10 295±4356, 32 994±25 449; PANOVA<0.05). There was a significant positive correlation between the %MTR and the histological protein content of the thrombus (r=0.70; P<0.05). The apparent diffusion coefficient was lower in erythrocyte-rich and collagen-rich thrombus (0.72±0.10 and 0.69±0.05 [×10(-3) mm(2)/s]). Thrombus at days 7 and 14 had the highest apparent diffusion coefficient values (0.95±0.09 and 1.10±0.18 [×10(-3) mm(2)/s]).

CONCLUSIONS

MT and diffusion-weighted magnetic resonance imaging sequences are promising for the staging of thrombus composition and could be useful in guiding medical intervention.

Leukocytes and the natural history of deep vein thrombosis: current concepts and future directions

Observational studies have shown that inflammatory cells accumulate within the thrombus and surrounding vein wall during the natural history of venous thrombosis. More recent studies have begun to unravel the mechanisms that regulate this interaction and have confirmed that thrombosis and inflammation are intimately linked. This review outlines our current knowledge of the complex relationship between inflammatory cell activity and venous thrombosis and highlights new areas of research in this field. A better understanding of this relationship could lead to the development of novel therapeutic targets that inhibit thrombus formation or promote its resolution.