The in vivo diagnosis of early‐stage aortic valve sclerosis using magnetic resonance imaging in a rabbit model

Purpose

To use magnetic resonance imaging (MRI) to identify and monitor early aortic valve sclerosis (AVS) induced by cholesterol feeding in rabbits. AVS is a highly prevalent disease process, affecting more than 25% of the population over age 65. A major obstacle to early stage medical management of AVS has been the lack of an objective noninvasive technique to identify its presence and monitor its progress.

Materials and Methods

Retrospectively gated CINE fast spoiled gradient echo (fSPGR) images of aortic valve cusps were collected at 3‐month intervals starting at 6 months using a 1.5 T MR scanner interfaced with a customized surface radiofrequency coil. At 16 months a subset of animals was sacrificed and excised cusps were examined with both high frequency ultrasound (US) and histopathological techniques to validate the MRI method.

Results

MR and US analysis identified significant thickening of diseased AV cusps when compared to control (P < 0.05). Histopathological analysis confirmed the presence of human‐like AVS in diseased rabbit valves.

Conclusion

Early AVS, exemplified by increased valve thickness, can be identified in vivo using high‐resolution MRI. J. Magn. Reson. Imaging 2009;29:825–831. © 2009 Wiley‐Liss, Inc.     

Bicuspid aortic valves: Diagnostic accuracy of standard axial 64-slice chest CT compared to aortic valve image plane ECG-gated cardiac CT

Objectives

To assess the diagnostic accuracy of standard axial 64-slice chest CT compared to aortic valve image plane ECG-gated cardiac CT for bicuspid aortic valves.

Materials and methods

The standard axial chest CT scans of 20 patients with known bicuspid aortic valves were blindly, randomly analyzed for (i) the appearance of the valve cusps, (ii) the largest aortic sinus area, (iii) the longest aortic cusp length, (iv) the thickest aortic valve cusp and (v) valve calcification. A second blinded reader independently analyzed the appearance of the valve cusps. Forty-two age- and sex-matched patients with known tricuspid aortic valves were used as controls. Retrospectively ECG-gated cardiac CT multiphase reconstructions of the aortic valve were used as the gold-standard.

Results

Fourteen (21%) scans were scored as unevaluable (7 bicuspid, 7 tricuspid). Of the remainder, there were 13 evaluable bicuspid valves, ten of which showed an aortic valve line sign, while the remaining three showed a normal Mercedes-Benz appearance owing to fused valve cusps. The 35 evaluable tricuspid aortic valves all showed a normal Mercedes-Benz appearance (P = 0.001). Kappa analysis = 0.62 indicating good interobserver agreement for the aortic valve cusp appearance. Aortic sinus areas, aortic cusp lengths and aortic cusp thicknesses of ≥3.8 cm², 3.2 cm and 1.6 mm respectively on standard axial chest CT best distinguished bicuspid from tricuspid aortic valves (P < 0.0001 for all). Of evaluable scans, the sensitivity, specificity, positive and negative predictive values of standard axial chest CT in diagnosing bicuspid aortic valves was 77% (CI 0.54–1.0), 100%, 100% and 70% respectively.

Conclusion

The aortic valve is evaluable in approximately 80% of standard chest 64-slice CT scans. Bicuspid aortic valves may be diagnosed on evaluable scans with good diagnostic accuracy. An aortic valve line sign, enlarged aortic sinuses and elongated, thickened valve cusps are specific CT features.     

Neurovascular changes measured by time‐of‐flight MR angiography in cholesterol‐fed rabbits with cortical amyloid β‐peptide accumulation

Purpose:

To test the hypothesis that narrowing of cranial blood vessels in cholesterol‐fed rabbits is a function of the duration of the high cholesterol diet. Such neurovascular changes, caused by elevated serum cholesterol, are linked to stroke and Alzheimer's disease risk.

Materials and Methods:

Four groups of New Zealand White rabbits were studied. Six were fed a normal diet, 19 were fed a 2% cholesterol diet with 0.12 ppm copper in the drinking water for 8 weeks, 10 weeks, or 12 weeks. Time‐of‐flight (TOF) MR angiography (MRA) at 3 Tesla was used to measure arterial diameters in 11 vessels. Previously published data for amyloid β‐peptide (Aβ) accumulation in the brains measured postmortem were correlated to vessel diameters. Ventricular volumes of rabbits were measured on group‐averaged data.

Results:

Several vessel diameters decreased with cholesterol diet duration. The posterior communicating arteries showed the largest significant effect. Aβ accumulation was inversely correlated with arterial diameter. Ventricular volumes between the normal diet and 12 weeks cholesterol‐fed groups were not significantly different.

Conclusion:

Reduction in vessel diameter of medium‐sized vessels but not large vessels was measured in these hypercholesterolemic rabbits. The vessel diameter narrowing and cortical Aβ deposition occurred before measurable ventricular enlargement. J. Magn. Reson. Imaging 2010;32:306–314. © 2010 Wiley‐Liss, Inc.     

Variables affecting the accuracy of MDCT in prediction of the proper prosthesis deployment projection for transcatheter aortic valve implantation

Objective

We evaluated multidetector computed tomography (MDCT) accuracy for the prediction of the optimal prosthetic aortic valve deployment angle in trans-catheter aortic valve implantation (TAVI) with the different variables.

Assessment of macrophage infiltration in a Murine model of abdominal aortic aneurysm

Purpose

To evaluate the use of an ultrasmall superparamagnetic iron oxide (USPIO) contrast agent as a marker for the detection of macrophage in a preclinical abdominal aortic aneurysm animal (AAA) model.

Materials and Methods

Osmotic pumps were implanted subcutaneously in apoE^?/? mice for continuous infusion of Angiotensin II (Ang‐II). Weekly bright‐blood gradient echo scans were performed on the suprarenal abdominal aorta to evaluate aneurysm development. Once an AAA was detected, animals were administered 1000 μmol/kg of the USPIO contrast agent ferumoxtran‐10 (Combidex®) followed by in vivo scanning 24 h post‐USPIO administration. After in vivo imaging, aortas were harvested for ex vivo imaging, histology, iron quantification, and gene expression analysis.

Results

Reduced signal intensity was evident in the post‐USPIO transverse images of the abdominal aorta. The areas of reduced signal were primarily along the aneurysm shoulder and outer perianeurysm areas and corresponded to regions of macrophage infiltration and colocalized USPIO determination by means of histological staining. The absolute iron content measured significantly correlated to the area of signal reduction in the ex vivo images (r = 0.9; P < 0.01). In the AAA tissue, the macrophage‐driven cytokine gene expression was up‐regulated along with a matrix metalloproteinase known to mediate extracellular matrix breakdown in this disease model.

Conclusion

These results demonstrate the feasibility of using an USPIO contrast agent as a surrogate for detecting the acute inflammatory process involved in the development of abdominal aneurysms. J. Magn. Reson. Imaging 2009;30:455–460. Published by Wiley‐Liss, Inc.

     

Detection of experimental atherosclerosis with indium-111 radiolabelled hematoporphyrin derivative

It has been observed that atherosclerotic lesions (AL) concentrate certain porphyrins. We evaluated the usefulness of 111In-labelled Photofrin II (PFII), a porphyrin derived from haematoporphyrin derivative, for detection of experimental AL in cholesterol fed rabbits. Three groups of rabbits were studied: non-atherosclerotic (n = 3), 6 and 12 week cholesterol fed (n = 4, 3). 111In-PFII was injected intravenously and gamma camera images were obtained at 24 and 48 h. At 48 h, explanted aortas were also imaged. Aortic arch (AA) to background (BKG) count ratios were calculated from images of the whole body and explanted aortas. AA/BKG ratios were significantly higher in the 12 week cholesterol fed rabbits (3.9 +/- 0.72 at 24 h) and (4.0 +/- 0.67 at 48 h) than in the non-atherosclerotic rabbits (2.2 +/- 0.07 at 24 h) and (2.3 +/- 0.18 at 48 h) (p less than 0.05). The AA/BKG ratio for the explanted aortas showed similar results. Additionally, in two of three 12 week cholesterol fed rabbits, focal count deposition was visible on the whole animal images at the site of aortic arch atherosclerosis. We conclude that 111In-PFII concentrates in AL as early as 24 h after injection and has the potential to be used as an imaging agent for experimental atherosclerosis.     

Measurement of Opening and Closing Angles of Aortic Valve Prostheses In Vivo Using Dual-Source Computed Tomography: Comparison with Those of Manufacturers' in 10 Different Types

Objective

The aims of this study were to compare opening and closing angles of normally functioning mechanical aortic valves measured on dual-source computed tomography (CT) with the manufacturers'' values and to compare CT-measured opening angles according to valve function.

Materials and Methods

A total of 140 patients with 10 different types of mechanical aortic valves, who underwent dual-source cardiac CT, were included. Opening and closing angles were measured on CT images. Agreement between angles in normally functioning valves and the manufacturer values was assessed using the interclass coefficient and the Bland-Altman method. CT-measured opening angles were compared between normal functioning valves and suspected dysfunctioning valves.

Results

The CT-measured opening angles of normally functioning valves and manufacturers'' values showed excellent agreement for seven valve types (intraclass coefficient [ICC], 0.977; 95% confidence interval [CI], 0.962-0.987). The mean differences in opening angles between the CT measurements and the manufacturers'' values were 1.2° in seven types of valves, 11.0° in On-X valves, and 15.5° in ATS valves. The manufacturers'' closing angles and those measured by CT showed excellent agreement for all valve types (ICC, 0.953; 95% CI, 0.920-0.972). Among valves with suspected dysfunction, those with limitation of motion (LOM) and an increased pressure gradient (PG) had smaller opening angles than those with LOM only (p < 0.05).

Conclusion

Dual-source cardiac CT accurately measures opening and closing angles in most types of mechanical aortic valves, compared with the manufacturers'' values. Opening angles on CT differ according to the type of valve dysfunction and a decreased opening angle may suggest an elevated PG.     

Untersuchungstechniken und Stellenwert der CT bei der Diagnostik von Herzklappenerkrankungen

Clinical/methodical issue

Cardiac computed tomography (CT) is the first-line modality for coronary assessment. In addition valvular morphology and function can be evaluated.

Standard radiological methods

The method of choice for the evaluation of cardiac valves is echocardiography, followed by magnetic resonance imaging.

Methodical innovations

Recent technical improvements and advances in temporal resolution allow a detailed anatomical and functional evaluation of the cardiac valves.

Performance

Cardiac CT provides an excellent image quality of the aortic and mitral valve thus enabling an evaluation of the morphology. In addition, cardiac CT allows an assessment of aortic valve function with respect to the grading of stenosis and regurgitation.

Achievements

Cardiac CT is not considered the first-line modality for the evaluation of cardiac valves; however, beyond coronary assessment CT provides important information on the morphology and function of cardiac valves.

Practical recommendations

Cardiac CT can be a useful imaging alternative for patients in whom other more commonly used methods, such as echocardiography and magnetic resonance imaging fail to provide the necessary information.     

Visualization of aortic valve leaflets using black blood MRI.

Although magnetic resonance imaging (MRI) is capable of imaging various physiological parameters associated with the heart valves, it has generally been difficult to visualize the valve leaflets directly. The aortic valve was imaged in 120 patients referred for cardiac MRI to assess myocardial volumes or mass. The average patient age was 37 and ranged from 9 to 75 years. Heart rate ranged from 43 to 100 bpm. Imaging was performed on a 1.5 T scanner equipped with enhanced gradients and a cardiac phased-array coil. A double inversion recovery fast spin-echo sequence was used to acquire short-axis images of the aortic valve in a breath-hold (15 +/- 3 seconds). All three leaflets of the aortic valve were seen in 102 of 120 studies (85%). Two leaflets were detected in another 15 subjects. No leaflets were seen in three individuals. Seven cases of a bicuspid or thickened aortic valves were clearly distinguished from normal valves. The signal-to-noise ratio of aortic leaflets (14 +/- 5) was significantly higher than that of the residual blood signal in the aortic root (7 +/- 4, P < 0.001). MR images showed the aortic valve leaflets in a high fraction of people with suspected normal aortic valves and detected seven cases of abnormal aortic valves. The potential of MRI to study both the anatomic and functional consequences of valvular heart disease warrants further study. J. Magn. Reson. Imaging 1999;10:771-777.     

Analysis of pulse wave velocity in the thoracic aorta by flow-sensitive four-dimensional MRI: reproducibility and correlation with characteristics in patients with aortic atherosclerosis

Purpose:

To measure aortic pulse wave velocity (PWV) using flow‐sensitive four‐dimensional (4D) MRI and to evaluate test–retest reliability, inter‐ and intra‐observer variability in volunteers and correlation with characteristics in patients with aortic atherosclerosis.

Materials and Methods:

Flow‐sensitive 4D MRI was performed in 12 volunteers (24 ± 3 years) and 86 acute stroke patients (68 ± 9 years) with aortic atherosclerosis. Retrospectively positioned 28 ± 4 analysis planes along the entire aorta (inter‐slice‐distance = 10 mm) and frame wise lumen segmentation yielded flow‐time‐curves for each plane. Global aortic PWV was calculated from time‐shifts and distances between the upslope portions of all available flow‐time curves.

Results:

Inter‐ and intra‐observer variability of PWV measurements in volunteers (7% and 8%) was low while test–retest reliability (22%) was moderate. PWV in patients was significantly higher compared with volunteers (5.8 ± 2.9 versus 3.8 ± 0.8 m/s; P = 0.02). Among 17 patient characteristics considered, statistical analysis revealed significant (P < 0.05) but low correlation of PWV with age (r = 0.25), aortic valve insufficiency (r = 0.29), and pulse pressure (r = 0.28). Multivariate modeling indicated that aortic valve insufficiency and elevated pulse pressure were significantly associated with higher PWV (adjusted R² = 0.13).

Conclusion:

Flow‐sensitive 4D MRI allows for estimating aortic PWV with low observer dependence and moderate test–retest reliability. PWV in patients correlated with age, aortic valve insufficiency, and pulse pressure. J. Magn. Reson. Imaging 2012;35:1162‐1168. © 2012 Wiley Periodicals, Inc.     

Effect of disease progression on liver apparent diffusion coefficient and T2 values in a murine model of hepatic fibrosis at 11.7 Tesla MRI

Purpose:

To evaluate the effects of hepatic fibrosis on ADC and T₂ values of ex vivo murine liver specimens imaged using 11.7 Tesla (T) MRI.

Materials and Methods:

This animal study was IACUC approved. Seventeen male, C57BL/6 mice were divided into control (n = 2) and experimental groups (n = 15), the latter fed a 3, 5‐dicarbethoxy‐1, 4‐dihydrocollidine (DDC) supplemented diet, inducing hepatic fibrosis. Ex vivo liver specimens were imaged using an 11.7T MRI scanner. Spin‐echo pulsed field gradient and multi‐echo spin‐echo acquisitions were used to generate parametric ADC and T₂ maps, respectively. Degrees of fibrosis were determined by the evaluation of a pathologist as well as digital image analysis. Scatterplot graphs comparing ADC and T₂ to degrees of fibrosis were generated and correlation coefficients were calculated.

Results:

Strong correlation was found between degrees of hepatic fibrosis and ADC with higher degrees of fibrosis associated with lower hepatic ADC values. Moderate correlation between hepatic fibrosis and T₂ values was seen with higher degrees of fibrosis associated with lower T₂ values.

Conclusion:

Inverse relationships between degrees of fibrosis and both ADC and T₂ are seen, highlighting the utility of these parameters in the ongoing development of an MRI methodology to quantify hepatic fibrosis. J. Magn. Reson. Imaging 2012;35:140‐146. © 2011 Wiley Periodicals, Inc.     

Evaluation of neovessels in atherosclerotic plaques of rabbits using an albumin-binding intravascular contrast agent and MRI

Purpose

To test whether B‐22956/1, a novel intravascular contrast agent with a high affinity to serum albumin (Bracco Imaging SpA.), allowed quantifying neovessel and macrophage density in atherosclerotic plaques of rabbits using MRI.

Materials and Methods

A T1‐weighted MRI of the aorta was acquired in 10 rabbits (7 atherosclerotic and 3 control rabbits) before and up to 2 h after intravenous injection of 100 μmol/kg of Gd‐DTPA or 75 μmol/kg of B‐22956/1. Plaque enhancement was measured at different time points. Immunohistochemistry was performed using anti‐CD 31 antibodies and anti‐RAM 11 antibodies to correlate to neovessel and macrophage density, respectively.

Results

MRI showed a significant plaque enhancement 2 h after B‐22956/1 versus Gd‐DTPA in the atherosclerotic group (39.75% versus 9.5%; P < 0.0001. Early atherosclerotic plaques (n = 146) enhancement positively correlates with neovessel density on corresponding histological sections (r = 0.42; P < 0.01). Enhancement of atherosclerotic plaques 2 h after injection of B‐22956/1 correlated with macrophage density (r = 0.71; P < 0.01).

Conclusion

Enhancement of atherosclerotic plaques with MRI correlated with neovessel density at early time points after the injection of B‐22956/1 and with macrophage density, at later time points. Hence, B‐22956/1‐enhanced MRI represents a promising imaging technique for the identification of “high‐risk” plaques. J. Magn. Reson. Imaging 2008;27:1406–1411. © 2008 Wiley‐Liss, Inc.     

Combined off-resonance imaging and T2 relaxation in the rotating frame for positive contrast MR imaging of infection in a murine burn model

Purpose

To develop novel magnetic resonance (MR) imaging methods to monitor accumulation of macrophages in inflammation and infection. Positive‐contrast MR imaging provides an alternative to negative‐contrast MRI, exploiting the chemical shift induced by ultra‐small superparamagnetic iron‐oxide (USPIO) nanoparticles to nearby water molecules. We introduce a novel combination of off‐resonance (ORI) positive‐contrast MRI and T_2ρ relaxation in the rotating frame (ORI‐T_2ρ) for positive‐contrast MR imaging of USPIO.

Materials and Methods

We tested ORI‐T_2ρ in phantoms and imaged in vivo the accumulation of USPIO‐labeled macrophages at the infection site in a mouse model of burn trauma and infection with Pseudomonas aeruginosa (PA). PA infection is clinically important. The USPIO nanoparticles were injected directly in the animals in solution, and macrophage labeling occurred in vivo in the animal model.

Results

We observed a significant difference between ORI‐T_2ρ and ORI, which leads us to suggest that ORI‐T_2ρ is more sensitive in detecting USPIO signal. To this end, the ORI‐T_2ρ positive contrast method may prove to be of higher utility in future research.

Conclusion

Our results may have direct implications in the longitudinal monitoring of infection, and open perspectives for testing novel anti‐infective compounds. J. Magn. Reson. Imaging 2010;32:1172–1183. © 2010 Wiley‐Liss, Inc.     

Breathhold time‐resolved three‐directional MR velocity mapping of aortic flow in patients after aortic valve‐sparing surgery

Purpose

To evaluate the utility of breathhold time‐resolved three‐directional MR velocity mapping for quantifying the restoration of normal flow patterns in patients after aortic valve‐sparing surgery.

Materials and Methods

Breathhold time‐resolved three‐directional MR velocity mapping was performed on 13 patients with aortic valve‐sparing surgery. Ten healthy volunteers and 12 patients with ascending aortic aneurysm underwent the same MR examination for comparison. Aortic laminar flow, turbulent flow, and the presence of vortical flow in the sinuses of Valsalva were semiquantitatively assessed and statistically compared between the three groups of subjects.

Results

The average score of laminar flow in the ascending aorta for patients with surgery was not significantly different from that of volunteers (P = 0.210), but was significantly greater than that of patients with aneurysm (P < 0.01). The average score of turbulent flow in patients with surgery was significantly smaller than that of patients with aneurysm (P < 0.01). The presence of systolic vortical flow in the sinuses of Valsalva for patients with surgery was not significantly different from that of healthy volunteers (P = 0.405) and patients with aneurysm (P = 0.238).

Conclusion

Breathhold time‐resolved three‐directional MR velocity mapping allows for quantifying flow patterns in the aortic root and ascending aorta. Normal laminar flow in the ascending aorta and vortical flow in the sinuses of Valsalva can be restored in patients after aortic valve‐sparing surgery. J. Magn. Reson. Imaging 2009;29:569–575. © 2009 Wiley‐Liss, Inc.     

USPIO (Ferumoxtran-10)-enhanced MRI to visualize reticuloendothelial system cells in neonatal rats: feasibility and biodistribution study

Purpose

To investigate whether USPIO‐enhanced magnetic resonance imaging (MRI) detected reticuloendothelial system (RES) cells in newborn normal rats.

Materials and Methods

Newborn normal rats were imaged in vivo on a 1.5 T MR system, 2–96 hours after intraperitoneal Ferumoxtran‐10 (n = 38) or saline injection (control group, n = 5). Signals from liver, spleen, and vertebral bone marrow were measured (T2‐weighted Turbo Spin Echo) to describe the kinetics of enhancement. The pups were sacrificed and iron concentrations in plasma and peritoneal fluid were measured using atomic absorption spectrometry. Prussian blue‐labeled cells density in liver, spleen, and vertebral bone marrow was assessed.

Results

Significant (P < 0.05) negative enhancement of the liver, spleen, and vertebral bone marrow was noted after Ferumoxtran‐10 injection (2–96 hours for liver and spleen, 4–96 hours for bone marrow). Ferumoxtran‐10 was absorbed from the peritoneum in the first 8 hours postinjection, entering the circulation with a plasma peak (8 hours); then Ferumoxtran‐10 returned over the baseline in plasma (96 hours). Important intracellular iron deposition in liver and spleen was measured postinjection (3–96 hours, P < 0.05). Limited but significant intracellular iron deposition was noted in vertebral bone marrow postinjection (96 hours, P < 0.05), suggesting that Ferumoxtran‐10 selectively labeled RES cells after 96 hours and produced nonspecific labeling at earlier timepoints.

Conclusion

Ferumoxtran‐10‐enhanced MRI visualizes RES cells in vivo in newborn rats. J. Magn. Reson. Imaging 2008;28:1046–1052. © 2008 Wiley‐Liss, Inc.     

Accelerated aortic imaging using small field of view imaging and electrocardiogram-triggered quadruple inversion recovery magnetization preparation

Purpose:

To accelerate and optimize black blood properties of the quadruple inversion recovery (QIR) technique for imaging the abdominal aortic wall.

Materials and Methods:

QIR inversion delays were optimized for different heart rates in simulations and phantom studies by minimizing the steady state magnetization of blood for T₁ = 100–1400 ms. To accelerate and improve black blood properties of aortic vessel wall imaging, the QIR prepulse was combined with zoom imaging and (a) “traditional” and (b) “trailing” electrocardiogram (ECG) triggering. Ten volunteers were imaged pre‐ and post‐contrast administration using a conventional ECG‐triggered double inversion recovery (DIR) and the two QIR implementations in combination with a zoom‐TSE readout.

Results:

The QIR implemented with “trailing” ECG‐triggering resulted in consistently good blood suppression as the second inversion delay was timed during maximum systolic flow in the aorta. The blood signal‐to‐noise ratio and vessel wall to blood contrast‐to‐noise ratio, vessel wall sharpness, and image quality scores showed a statistically significant improvement compared with the traditional QIR implementation with and without ECG‐triggering.

Conclusion:

We demonstrate that aortic vessel wall imaging can be accelerated with zoom imaging and that “trailing” ECG‐triggering improves black blood properties of the aorta which is subject to motion and variable blood flow during the cardiac cycle. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

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.     

High-resolution MRI of excised human prostate specimens acquired with 9.4T in detection and identification of cancers: validation of a technique

Purpose:

To evaluate feasibility of high‐resolution, high‐field ex vivo prostate magnetic resonance imaging (MRI) as an aid to guide pathologists' examination and develop in vivo MRI methods.

Materials and Methods:

Unfixed excised prostatectomy specimens (n = 9) were obtained and imaged immediately after radical prostatectomy under an Institutional Review Board‐approved protocol. High‐resolution T2‐weighted (T2W) MRI of specimens were acquired with a Bruker 9.4 T scanner to correlate with whole‐mount histology. Additionally, T2 and apparent diffusion coefficient (ADC) maps were generated.

Results:

By visual inspection of the nine prostate specimens imaged, high‐resolution T2W MRI showed improved anatomical detail compared to published low‐resolution images acquired at 4 T as published by other investigators. Benign prostatic hyperplasia, adenocarcinomas, curvilinear duct architecture distortion due to adenocarcinomas, and normal radial duct distribution were readily identified. T2 was ≈10 msec longer (P < 0.03) and the ADC was ≈1.4 times larger (P < 0.002) in the normal peripheral zone compared to the peripheral zone with prostate cancer.

Conclusion:

Differences in T2 and ADC between benign and malignant tissue are consistent with in vivo data. High‐resolution, high‐field MRI has the potential to improve the detection and identification of prostate structures. The protocols and techniques developed in this study could augment routine pathological analysis of surgical specimens and guide treatment of prostate cancer patients. J. Magn. Reson. Imaging 2011. © 2011 Wiley‐Liss, Inc.     

MRI study of atherosclerotic plaque progression using ultrasmall superparamagnetic iron oxide in Watanabe heritable hyperlipidemic rabbits

Objective:

The purpose of this study was to evaluate plaque progression by using MRI with ultrasmall superparamagnetic iron oxide (USPIO) and by histopathological studies.

Methods:

We divided 12 Watanabe heritable hyperlipidemic (WHHL) rabbits into 4 groups based on their age (3, 9, 14 and 26 months) and injected them intravenously with 0.8 mmol (Fe) kg⁻¹ of USPIO (size, 32 nm; concentration, 15 mg dl⁻¹). On the fifth post-injection day, they were again given an intravenous injection with 40 μmol kg⁻¹ of the same USPIO, and MR angiography (MRA) was performed. The signal-to-noise ratio (SNR) in regions of interest in the wall of the upper abdominal aorta was calculated on coronal images. Specimens from the same level of the aorta were subjected to iron staining and RAM-11 immunostaining and used for histopathological study. For statistical analysis of the MRA and histopathological findings, we used analysis of variance [Tukey''s honest significant difference (HSD) test].

Results:

In 9-month-old rabbits, the SNR was significantly lower than in rabbits of the other ages (p < 0.01), and the area of RAM-11 (DAKO Corporation, Glostrup, Denmark) and iron uptake in the aortic wall was significantly larger (RAM-11, p < 0.01; iron, p < 0.05). These areas were the smallest in 3-month-old rabbits.

Conclusion:

Histopathologically, the number of macrophages was the greatest in 9-month-old rabbits. Our findings indicate that the SNR on MRI scans reflects the number of macrophages in the aortic wall of WHHL rabbits.

Advances in knowledge:

USPIO-enhanced MRI visualized the accumulation of macrophages in early atherosclerotic plaques of WHHL rabbits in the course of natural progression.