In vivo magnetic resonance imaging of large spontaneous aortic aneurysms in old apolipoprotein E-deficient mice

Old ApoE-deficient mice were studied in vivo by magnetic resonance imaging (MRI) to prospectively evaluate vascular remodeling associated with atherosclerotic lesions. MATERIAL AND METHODS: Old female ApoE-/- mice on a normal diet were followed by MRI at 2 Tesla for a 3-month period and killed for histopathology. Aortic dimensions were measured and compared. RESULTS: High-quality in vivo MR images were obtained at 2 Tesla with in plane spatial resolution of 86 X 86 microm2. On MRI, aortic lumen enlargement (>1.5-fold dilation) was seen in 10 of 13 mice, located predominantly in the suprarenal portion of the aorta. The mean maximal diameter of the aneurysms and of the aorta above and below the aneurysm were, respectively, 1.12 +/- 0.32 mm and 0.53 +/- 0.08 mm by MRI and 1.3+/- 0.41 mm and 0.55 +/- 0.15 mm by histology. Matched histologic cross-sections of the aortic wall showed medial degradation with rupture of the internal elastic lamina at multiple sites, associated with fibrolipidic plaque containing cholesterol crystals. CONCLUSIONS: Aortic lumen enlargement was diagnosed in old ApoE-/- mice at sites with advanced atherosclerotic plaques. MRI has potential both as an in vivo imaging technique for screening mouse models for vascular wall pathology and to follow arterial remodeling associated with the disease progression.     

High-resolution MRI with cardiac and respiratory gating allows for accurate in vivo atherosclerotic plaque visualization in the murine aortic arch.

Genetically engineered mouse models provide enormous potential for investigation of the underlying mechanisms of atherosclerotic disease, but noninvasive imaging methods for analysis of atherosclerosis in mice are currently limited. This study aimed to demonstrate the feasibility of MRI to noninvasively visualize atherosclerotic plaques in the thoracic aorta in mice deficient in apolipoprotein-E, who develop atherosclerotic lesions similar to those observed in humans. To freeze motion, MR data acquisition was both ECG- and respiratory-gated. T(1)-weighted MR images were acquired with TR/TE approximately 1000/10 ms. Spatial image resolution was 49 x 98 x 300 micro m(3). MRI revealed a detailed view of the lumen and the vessel wall of the entire thoracic aorta. Comparison of MRI with corresponding cross-sectional histopathology showed excellent agreement of aortic vessel wall area (r = 0.97). Hence, noninvasive MRI should allow new insights into the mechanisms involved in progression and regression of atherosclerotic disease.     

High-resolution, multicontrast three-dimensional-MRI characterizes atherosclerotic plaque composition in ApoE-/- mice ex vivo

PURPOSE: To systematically investigate intrinsic MR contrast mechanisms that would facilitate plaque characterization and quantification in the aortic root and brachiocephalic artery of ApoE-/- mice ex vivo. MATERIALS AND METHODS: To establish unambiguous MR parameters for routinely analyzing atherosclerotic plaque ex vivo at 11.7 T, relaxation times of plaque components were quantitatively assessed. Magnetization transfer and lipid-proton three-dimensional MR imaging was investigated for visualization of collagen- and lipid-rich plaque regions, respectively. A three-dimensional multiecho sequence with a spatial resolution of 47 x 47 x 63 microm was implemented providing a variable degree of T2-weighting. RESULTS: Relaxation time measurements showed clear tissue heterogeneity between atherosclerotic plaque components in the T2-values, but similar T1-values at 11.7 T (T1/T2 mean +/- SD; cellular plaque component: 1.2 +/- 0.3 seconds/26.3 +/- 0.4 msec; fibrofatty plaque component: 1.1 +/- 0.2 seconds/13.7 +/- 2.0 msec). The three-dimensional multiecho sequence allowed the calculation of the intrinsic proton density and T2-maps. The sum of the multiecho data provided strong T2-weighting that facilitated quantification of various components of atherosclerotic plaque in the mouse aortic root and correlated well with histology (P < 0.0001). CONCLUSION: High-resolution MRI allows for accurate classification and quantification of atherosclerotic plaque components in the aortic root of mice.     

Mice with a deletion in the first intron of the Col1a1 gene develop dissection and rupture of aorta in the absence of aneurysms: high-resolution magnetic resonance imaging, at 4.7 T, of the aorta and cerebral arteries.

Deletion of the majority of the first intron of the Col1a1 gene in mice leads to decreased type I collagen synthesis and content in the aortic wall. In 54% of cases, mice homozygous for the Col1a1 mutation die of thoracic hemorrhage by the age of 18 months. It is unknown whether the fatal bleeding results from an acute dissection of the aortic wall or a gradually developing dilatation of the medial layer prior to rupture. We optimized high-resolution MRI methods using a 4.7 T MR scanner to obtain in vivo images of the entire mouse aorta. The MR images were acquired in three imaging planes using gradient echo, spin echo, and spin echo with inversion recovery pulse sequences with a maximum in-plane resolution of 68 x 68 microm and acquisition times less than 10 min. In five Col1a1 mutated mice aged 16 months, the MR images showed no signs of aneurysmal dilatation, wall defects, or former dissection, suggesting that the mechanism for aortic rupture is an acute dissection of the aortic medial layer. Cerebral arteries were imaged using a three-dimensional time of fight pulse sequence. The resolution of 73 x 73 x 94 microm showed normal cerebral arteries. Histology showed a 22% thinner cerebral artery wall in Col1a1 mutated mice.     

Multislice dark-blood carotid artery wall imaging: a 1.5 T and 3.0 T comparison

PURPOSE: To compare two multislice turbo spin-echo (TSE) carotid artery wall imaging techniques at 1.5 T and 3.0 T, and to investigate the feasibility of higher spatial resolution carotid artery wall imaging at 3.0 T. MATERIALS AND METHODS: Multislice proton density-weighted (PDW), T2-weighted (T2W), and T1-weighted (T1W) inflow/outflow saturation band (IOSB) and rapid extended coverage double inversion-recovery (REX-DIR) TSE carotid artery wall imaging was performed on six healthy volunteers at 1.5 T and 3.0 T using time-, coverage-, and spatial resolution-matched (0.47 x 0.47 x 3 mm3) imaging protocols. To investigate whether improved signal-to-noise ratio (SNR) at 3.0 T could allow for improved spatial resolution, higher spatial resolution imaging (0.31 x 0.31 x 3 mm3) was performed at 3.0 T. Carotid artery wall SNR, carotid lumen SNR, and wall-lumen contrast-to-noise ratio (CNR) were measured. RESULTS: Signal gain at 3.0 T relative to 1.5 T was observed for carotid artery wall SNR (223%) and wall-lumen CNR (255%) in all acquisitions (P < 0.025). IOSB and REX-DIR images were found to have different levels of SNR and CNR (P < 0.05) with IOSB values observed to be larger. Normalized to a common imaging time, the higher spatial resolution imaging at 3.0 T and the lower spatial resolution imaging at 1.5 T provided similar levels of wall-lumen CNR (P = NS). CONCLUSION: Multislice carotid wall imaging at 3.0 T with IOSB and REX-DIR benefits from improved SNR and CNR relative to 1.5 T, and allows for higher spatial resolution carotid artery wall imaging.     

High resolution MR imaging and localization of laser-induced thermal injury in the vascular wall

With the increasing use of lasers in surgical procedures, there is need for a noninvasive imaging modality to monitor laser–tissue interactions. MRI can be used readily for imaging human anatomy and holds the potential to map laser-induced thermal injury. This study investigates high resolution T1-weighted MR imaging of human aorta samples (in vitro) that have been damaged thermally using an argon ion laser and the corresponding histology. High resolution T1-weighted MR images (voxel size, .156 × .156 × .700 mm) clearly detected residual thermal injury as areas of bright signal intensity. Effective localization of thermal injury was achieved by subtraction of preinjury and postinjury slices with pseudocoloring of positive and negative differences. The results may serve as a basis from which to guide future in vivo studies.     

Superparamagnetic iron oxide-enhanced MRI of atherosclerotic plaques in Watanabe hereditable hyperlipidemic rabbits

RATIONALE AND OBJECTIVES: Inflammatory atherosclerotic plaques are characterized by increased endothelial permeability and multiple macrophages. Blood-pool MRI contrast agents like superparamagnetic iron oxide (SPIO) have an affinity for the monocyte-macrophage system and thus, may label inflammatory plaques. The objective was to demonstrate SPIO uptake in plaques of atherosclerotic rabbits by MRI and histology. METHODS: Aortas of anesthetized Watanabe hereditable hyperlipidemic rabbits were studied with a moderately T2*-weighted gradient-echo sequence at 1.5 T. Four groups of five animals each were studied: (1) without ultrasmall SPIO (carboxydextran coating; particle size, 25 nm; estimated plasma half-life, 6 hours) or with imaging after intravenous injection of SPIO at a dose (micromol Fe/kg) and postcontrast time delay (hours) of 50/8 (2), 50/24 (3), or 200/48 (4). In vivo MRI was compared with corresponding ex vivo histological iron stains. RESULTS: Animals receiving 200 micromol Fe/kg demonstrated areas of focal signal loss clearly confined to the aortic wall on a mean of 24 +/- 9 (31% +/- 11%) of 76 +/- 5 images compared with 0 +/- 0 of 76 +/- 5 images in controls (P = 0.009). The number of images with this finding in groups 2 and 3 was not significantly different compared with controls. By microscopy, SPIO-iron was seen in the endothelial cells and subendothelial intimal macrophages of atherosclerosis-prone aortic wall segments. Atherosclerotic lesions demonstrating iron uptake also showed a high macrophage content. CONCLUSIONS: SPIO accumulates in aortic plaques of atherosclerotic rabbits, producing a characteristic MRI finding. As SPIO accumulates in plaques with increased endothelial permeability and a high macrophage content, two established features of plaque inflammation, it may have a potential for noninvasive assessment of inflammatory atherosclerotic plaques.     

Quantifying tissue damage due to focused ultrasound heating observed by MRI.

Focused ultrasound heating of ex vivo bovine kidney and liver was monitored using magnetic resonance imaging (MRI) to investigate the quantitative relationship between time-dependent temperature elevations and altered contrast in MR images due to thermal coagulation. Proton resonance frequency shift MR thermometry was performed during heating at 10 sec intervals (single-slice fast spoiled GRASS [FSPGR], theta/TE/TR 30 degrees/11/39 msec, field of view 8 cm, 256 x 256, 3 mm slice thickness, 1 NEX); post-heating MR images were T1-weighted (3D-FSPGR, theta/TE/TR 60 degrees/25/200 msec, 1 mm slice thickness, 3 NEX). Analysis of the resulting temperature versus time data using the Arrhenius relationship and a simple binary discrimination model showed that thermal coagulation occurred with heating at approximately 54 degrees C for 10 sec in both tissues and could be predicted with approximately 625 microm spatial resolution. These results suggest that quantitative MR guidance of thermal coagulation therapy is feasible, and they provide information useful for designing future investigations in vivo.     

主动脉假性动脉瘤的影像诊断

目的：探讨主动脉假性动脉瘤的影像表现，评价MRI的诊断价值。方法：报道5例经手术证实的主动脉假性动脉瘤的影像所见，MRI检查4例，彩超检查3例，CT检查2例和主动脉造影1例。结果：胸、腹主动脉假性动脉瘤分别为3例和2例，假性动脉瘤位于主动脉轮廓外。彩超显示瘤体与主动脉有双向血流。CT和主动脉造影表现层状密度瘤体、早期强化和显影。MRI表现假性动脉瘤壁厚薄不均和信号不均质，均有破裂口。GRE显示经主动脉狭窄破裂口向瘤腔内喷射高信号血流。结论：MRI对假性动脉瘤的诊断有重要价值。     

Registration methodology for histological sections and in vivo imaging of human prostate

RATIONALE AND OBJECTIVES: Registration enables quantitative spatial correlation of features from different imaging modalities. Our objective is to register in vivo imaging with histologic sections of the human prostate so that histologic truth can be correlated with in vivo imaging features. MATERIALS AND METHODS: In vivo imaging of the prostate included T2-weighted anatomic and diffusion weighted 3-T magnetic resonance imaging (MRI) as well as 11C-choline positron emission tomography (PET). In addition, ex vivo 3-T MRI of the prostate specimen, histology, and associated block face photos of the prostate specimen were obtained. A standard registration method based on mutual information (MI) and thin-plate spline (TPS) was applied. Registration among in vivo imaging modalities is well established; however, accurate registration involving histology is difficult. Our approach breaks up the difficult direct registration of histology and in vivo imaging into achievable subregistration tasks involving intermediate ex vivo modalities like block face photography and specimen MRI. Results of subregistration tasks are combined to compute the intended, final registration between in vivo imaging and histology. RESULTS: The methodology was applied to two patients and found to be clinically feasible. Overall registered anatomic MRI, diffusion MRI, and 11C-choline PET aligned well with histology qualitatively for both patients. There is no ground truth of registration accuracy as the scans are real patient scans. An indirect validation of the registration accuracy has been proposed comparing tumor boundary markings found in diffusion MRI and histologic sections. Registration errors for two patients between diffusion MRI and histology were 3.74 and 2.26 mm. CONCLUSION: This proof of concept paper demonstrates a method based on intrinsic image information content for successfully registering in vivo imaging of the human prostate with its post-resection histology, which does not require the use of extrinsic fiducial markers. The methodology successfully mapped histology onto the in vivo imaging space, allowing the observation of how well different in vivo imaging features correspond to histologic truth. The methodology is therefore the basis for a systematic comparison of in vivo imaging for staging of human prostate cancer.     

Spontaneous acute dissection of the internal carotid artery: high-resolution magnetic resonance imaging at 3.0 tesla with a dedicated surface coil

PURPOSE: Magnetic Resonance Imaging (MRI) has become the method of choice in the evaluation of patients with suspected cervical artery dissection (CAD). However, reliable identification of acute CAD might be impaired by the limited spatial resolution of standard 1.5 T MRI. In this preliminary study, we implemented a multicontrast high-resolution noninvasive vessel wall imaging approach at 3.0 T in patients with spontaneous CAD. METHODS AND MATERIALS: Ten patients with CAD of the internal carotid artery (ICA) were included in the study. 3.0 T MRI (Gyroscan Intera, Philips) was acquired using a dedicated phased-array coil. MRI-protocol consisted of: (1) bright blood 3D inflow MRA (TR/TE/FA = 25 milliseconds/3.1 millisecond/16 degrees , 120 slices, reconstructed voxel size 0.3 x 0.3 x 0.8 mm); (2) black blood cardiac-gated water-selective T1w 3D spoiled GE (TR/TE/FA = 31 milliseconds/7.7 milliseconds/15 degrees , 36 slices, 0.3 x 0.3 x 1.0 mm); and (3) black blood cardiac triggered fat suppressed T2w TSE (TR/TE/ETL = 3 heart beats/44 milliseconds/7, 18 slices, 0.3 x 0.3 x 2 mm). Three observers in consensus performed image analysis. Special attention was paid to the integrity of the luminal and adventitial vessel boundary and the presence of a communicating intimal tear or flap. RESULTS: 3.0 T MRI provided excellent delineation of vessel lumen and vessel wall as a result of the nearly complete suppression of arterial blood signal. An intramural hematoma could be identified in all patients, confined between the luminal and adventitial vessel boundary. In no patient a communicating intimal tear could be identified. Clear distinction between intramural hematoma and thrombus was possible. CONCLUSION: High-resolution vessel wall imaging in patients with acute CAD is feasible. The increased signal-to-noise ratio at 3.0 T can be invested to obtain a higher spatial resolution, permitting depiction of intimal and adventitial vessel wall boundary and the intramural hematoma in the diseased vessel segment. The morphologic information that is gained is helpful in the understanding of the underlying pathomechanismen of CAD.     

Detection of amyloid plaques in mouse models of Alzheimer's disease by magnetic resonance imaging.

We performed three-dimensional, high-resolution magnetic resonance imaging (MRI) of fixed mouse brains to determine whether MRI can detect amyloid plaques in transgenic mouse models of Alzheimer's disease. Plaque-like structures in the cortex and hippocampus could be clearly identified in T2-weighted images with an image resolution of 46 microm x 72 microm x 72 microm. The locations of plaques were confirmed in coregistration studies comparing MR images with Congo red-stained histological results. This technique is quantitative, less labor-intensive compared to histology, and is free from artifacts related to sectioning process (deformation and missing tissues). It enabled us to study the distribution of plaques in the entire brain in 3D. The results of this study suggest that this method may be useful for assessing treatment efficacy in mouse models of Alzheimer's disease (AD).     

High-resolution magnetic resonance imaging of trabecular bone in the wrist at 3 tesla: initial results

PURPOSE: To evaluate the feasibility of high-resolution magnetic resonance imaging (MRI) of trabecular bone of the wrist at 3 Tesla (3T) in vivo and to assess the potential benefit of the increased resolution for clinical assessment of structural changes in spongy bone. MATERIAL AND METHODS: High-resolution MRI of the wrist was performed with a whole-body 3T MR scanner using a dedicated circularly polarized transmit-receive wrist-coil. Two 3D-FISP sequences with a spatial resolution of 300 x 300 x 300 microm3 in a measuring time of TA = 7:51 min, and 200 x 200 x 200 microm3 in TA = 9:33 min were applied. Seven young healthy volunteers and three elderly subjects with suspected osteoporosis were examined. The signal-to-noise ratio (SNR) in the optimized setup at 3T was compared to measurements at 1.5T. RESULTS: The images at 3T allow microscopic analysis of the bone structure at an isotropic spatial resolution of 200 microm in examination times of <10 min. Differences in the structure of the spongy bone between normal and markedly osteoporotic subjects are well depicted. The SNR at 3T was found up to 16 times higher than at 1.5T applying unchanged imaging parameters. CONCLUSION: The proposed high-resolution MRI technique offers high potential in the diagnosis and follow-up of diseases with impaired bone structure of hand and/or wrist in clinical applications.     

Magnetic resonance imaging of trabecular and cortical bone in mice: comparison of high resolution in vivo and ex vivo MR images with corresponding histology

Measurements of bone morphometry and remodeling have been shown to reflect bone strength and can be used to diagnose degenerative bone disease. In this study, in vivo and ex vivo magnetic resonance imaging (MRI) techniques to assess trabecular and cortical bone properties have been compared to each other and to histology as a novel means for the quantification of bone. Femurs of C57Bl/6 mice were examined both in vivo and ex vivo on an 11.7 T MRI scanner, followed by histologic processing and morphometry. A thresholding analysis technique was applied to the MRI images to generate contour lines and to delineate the boundaries between bone and marrow. Using MRI, an optimal correlation with histology was obtained with an in vivo longitudinal sectioned short echo time gradient-echo versus an in vivo long echo time spin-echo sequence or an ex vivo pulse sequence. Gradient-echo images were acquired with a maximum in-plane resolution of 35 microm. Our results demonstrated that in both the in vivo and ex vivo data sets, the percent area of marrow increases and percent area of trabecular bone and cortical bone thickness decreases moving from the epiphyseal growth plate to the diaphysis. These changes, observed with MRI, correlate with the histological data. Investigations using in vivo MRI gradient-echo sequences consistently gave the best correlation with histology. Our quantitative evaluation using both ex vivo and in vivo MRI was found to be an effective means to visualize non-invasively the normal variation in trabecular and cortical bone as compared to a histological "gold standard" The experiments validated in vivo MRI as a potential high resolution technique for investigating both soft tissue, such as marrow, and bone without radiation exposure.     

Comparison of 15 different stents in superficial femoral arteries by high resolution MRI ex vivo and in vivo

PURPOSE: To evaluate the MRI compatibility of 15 different commercially available, new generation, U.S. Food and Drug Administration (FDA)-approved stents suitable for deployment in superficial femoral arteries (SFAs), and to identify the ones that permit MRI to visualize the wall and lumen of stented arteries with sufficient spatial and contrast resolution to quantify restenosis after stent placement. MATERIALS AND METHODS: A total of 13 nitinol stents and two stainless-steel stents were placed in excised cadaveric SFAs and imaged by MRI at 1.5 T ex vivo. The images were evaluated qualitatively for the presence of artifacts and for the effects of the stent on image contrast, and quantitatively for the effect on signal-to-noise ratio (SNR) of the lumen of the artery inside the stent compared to the SNR of the fluid outside the artery. A nitinol stent was placed in the SFA of a 60-year-old man and imaged at 1.5 T in vivo. RESULTS: Both the vessel wall and the lumen could be visualized in cadaveric SFAs containing either the Absolute nitinol stent, the Dynalink nitinol stent, or the aSpire nitinol-covered stent. Their inside stent/outside stent SNR was 0.7, 0.8, and 0.8, respectively. The other 10 nitinol stents tested obscured the lumen but did not cause major image shape artifacts. Both stainless-steel stents tested, the WallGraft and WallStent, completely obscured the lumen and caused significant distortion of the image shapes. When the Dynalink stent was inserted into a highly stenosed SFA in vivo, the image showed a dark expanded eccentric lumen, circumscribed by a medium intensity band containing the stent. CONCLUSION: MRI can be used to visualize both the lumen and wall of SFAs containing selected nitinol stents ex vivo and in vivo. These results suggest that MRI can be used to monitor restenosis in stents placed in the femoral arterial bed.     

Hypointense boundary layer between slow flow and mural thrombus on spin-echo MR.

To evaluate the ability of spin-echo MRI to differentiate between slow flow and mural thrombus in aortic diseases, we reviewed the spin-echo MRI of 10 patients with intraaortic thrombus that had been documented by CT in 8 patients and aortography in 2 patients. Six patients had aortic aneurysms with mural thrombi, and four had aortic dissections with adherent mural thrombi within the false lumen. Five of seven gated oblique sagittal or coronal T1-weighted studies demonstrated hyperintense slow flow signal within the residual lumen. This hyperintense slow flow signal was accompanied by a parallel hypointense rim due to a boundary layer dephasing phenomenon. Eight axial T2-weighted MR studies demonstrated a hypointense zone due to fresh clot at the edge of a mural thrombus on even-echo images consistently. The hypointense boundary layer between slow flow and mural thrombus on either gated T1-weighted MRI or second-echo T2-weighted MRI not only predicted the presence of flow within the residual lumen but also clearly separated the area of slow flow from that of mural thrombus in 9 of 10 patients. Proper interpretation of spin-echo images may obviate the need for phase display imaging or gradient-echo imaging in differentiating between slow flow and mural thrombus.     

Vulnerable plaque detection by 3.0 tesla magnetic resonance imaging

RATIONALE AND OBJECTIVES: A clinical case report is presented on a 76-year-old man who volunteered for a 3.0 T magnetic resonance (MR) carotid protocol. The subject was referred for carotid endarterectomy and histology was performed on the ex vivo specimen and compared with the in vivo images. METHODS: The 3.0 and 1.5 T (obtained for comparison) MR protocol consisted of 2-dimensional (2D) and 3-dimensional (3D) multicontrast bright and black blood imaging for detecting the lumen and vessel wall. RESULTS: The combination of multicontrast black blood transverse images and the 3D time of flight transverse images provided visualization of a narrowed internal carotid artery lumen 4 mm above of the bifurcation and the presence of a complex atherosclerotic plaque containing a large lipid pool, calcification, and intact fibrous cap. Quantitative comparisons including vessel lumen and plaque area, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios were obtained for 1.5 and 3.0 T image data. Plaque composition was verified with histology. Macrophages were also detected in the shoulders of the plaque as demonstrated by CD68 staining and corresponded with a small hyperintense area in the T2W images at 3.0 T, but not observed in comparable 1.5 T images. CONCLUSIONS: High field 3.0 T multicontrast MRI of atherosclerotic plaque has been validated with histology comparison and provides improved detection of complex atherosclerotic plaque with increased SNR and CNR compared with 1.5 T. Further studies validating contrast mechanisms of plaque at 3.0 T are required, but atherosclerotic plaque imaging has clear benefit from application at the higher magnetic field strength.     

Characterization of aortic root atherosclerosis in ApoE knockout mice: high-resolution in vivo and ex vivo MRM with histological correlation.

In vivo, cardiac-gated, black-blood, and ex vivo magnetic resonance microscopy (MRM) images of the aortic root, and histopathology data were obtained from 12 transgenic and wild-type (WT) mice. MRM was performed using a black-blood imaging spin-echo sequence with upstream and downstream in-flow saturation pulses to obtain aortic root images in three contrast techniques: proton density-weighted (PDW), T(1)- (T(1)W), and T(2)-weighted (T(2)W). Aortic wall thickness and area were measured and correlated with histopathology data (R > 0.90). Ex vivo lesion components (lipid core, fibrous tissue, and cell tissue) were identified and characterized by differing image contrast in PDW, T(1)W, and T(2)W MRM, and by histopathology. The differences between WT and transgenic mice for maximal wall thickness and area were statistically significant (P < 0.05). This study demonstrates the feasibility of in vivo murine aortic root lesion assessment and ex vivo plaque characterization by MRM.     

Delivery and assessment of endovascular stents to repair aortic coarctation using MR and X-ray imaging

PURPOSE: To investigate the utility of MR and X-ray imaging for characterizing aortic coarctation and flow, and guiding the endovascular catheter to place a stent to repair the coarctation. MATERIALS AND METHODS: The descending aorta in eight dogs was looped with elastic band and tightened distal to the subclavian artery. Balanced fast field echo (bFFE) and velocity-encoded cine (VEC) MRI sequences were used for device tracking and measuring aortic flow. A T1-weighted fast-field echo sequence (T1-FFE) was used to visualize the coarctation and roadmap the aorta. Nitinol stents were guided by a nitinol guidewire and placed under MR guidance. RESULTS: Aortic coarctation was visible on MR and X-ray imaging. The procedure success rate was 88%. VEC MRI measured the changes in aortic flow (baseline = 1.3 +/- 0.2, coarctation = 0.2 +/- 0.02, and stent placement = 0.8 +/- 0.1 liters/minute). A significant reduction in iliac blood pressure was measured after coarctation, but it was reversed by stent placement. The stent lumen was visible on X-ray fluoroscopy, but not on MRI. CONCLUSION: Stent deployment to repair aortic coarctation is feasible under MR guidance. The combined use of MR and X-ray imaging is effective for anatomic and functional evaluation of aortic coarctation dilation, which may be crucial for optimal therapy.     

Intrabiliary MR imaging: assessment of biliary obstruction with use of an intraluminal MR receiver coil

PURPOSE: The primary aim of this study was to determine whether intrabiliary magnetic resonance (MR) imaging is feasible in a clinical setting and to optimize MR imaging parameters for the technique. In addition, it was attempted to determine the accuracy of intrabiliary MR imaging in the setting of biliary obstruction of unknown cause. MATERIALS AND METHODS: Intrabiliary MR was performed prospectively in 15 patients with biliary obstruction of unknown cause. A 0.030-inch MR intravascular receiver coil was placed in an existing biliary tube. Intrabiliary MR was performed on a 1.5-T system. T1-weighted, T2-weighted, and single-shot fast spin-echo images were acquired. T1-weighted images were also acquired after the administration of a gadolinium contrast agent. Signal intensity analysis was conducted in the region of the common bile duct. Accuracy of intrabiliary MR, computed tomography (CT), MR, and cholangiography were determined by correlation with surgical pathologic findings. RESULTS: Intrabiliary MR was successfully performed in 14 of 15 patients. MR examinations were performed in less than 1 hour. The signal-to-noise ratio in the region of the common bile duct with the intrabiliary MR technique was increased by a factor of 9 compared with standard surface-coil MR imaging (P < .00001). The mean n-plane resolution achieved was 740 +/- 20 microm x 1,150 +/- 20 microm obtained with use of a field of view of 18 cm x 18 cm (range, 15-24 cm) and a matrix of 256 x 160. Of the pulse sequences tested, the gadolinium-enhanced T1-weighted image was the best for identifying tumor and delineating tumor margins. Intrabiliary MR had a higher sensitivity than CT (100% vs 50%), a higher specificity than cholangiography (80% vs 20%), and a better correlation (P = .015) with surgical pathologic findings than CT, MR imaging, or cholangiography. CONCLUSIONS: Intrabiliary MR was well tolerated in a clinical setting and provided high spatial resolution and excellent contrast between the biliary lumen and adjacent structures. Intrabiliary MR demonstrated an advantage in detecting the presence or absence of biliary malignancies compared with currently available standard imaging techniques. The technique may be useful to evaluate biliary obstruction of unknown cause.