A mural thrombus of an infrarenal aortic aneurysm demonstrated as photon deficiency in a radionuclide study

Radionuclide angiogram (RNA) and aortogram may underestimate external aneurysmal diameter. Photon deficient areas are not uncommon along the abdominal aortic aneurysm (AAA) on RNA. To determine whether or not photon deficient areas along the aneurysm could represent a large thrombus, we studied radionuclide aortic angiography in thirty-eight patients during a preoperative cardiac gated study. All the patients (men, ages from 60 to 78) had CT, US, and/or aortogram for comparison. The presence of a thrombus was determined by CT, US, and/or surgical findings. Twelve of 38 (32%) patients’ RNA and blood pool images showed photon deficient areas along the aneurysmal walls having a large concentric or eccentric thrombus of the AAA. A large photon deficient area could be detected along the narrowing calibre of the aorta lumen. This finding results from a large mural thrombus being interposed between the left or right bowel/mesentery activity and the activity of the aneurysms functioning patent lumen. We concluded that a photon deficient area along an inferorenal aortic aneurysm may indicate a large thrombus of either eccentric or concentric type within an AAA.     

国产弹性蛋白酶浸泡法构建兔腹主动脉瘤及其随访

目的采用国产猪胰弹性蛋白酶溶液主动脉周浸泡法构建兔腹主动脉瘤(AAA)模型,并随访其长期稳定性。方法 24只新西兰兔随机分成两组,实验组(n=12)用10μL浓度为10 U/μL国产猪胰弹性蛋白酶溶液浸润主动脉近分叉处血管段30 min,对照组用10μL 0.9%氯化钠溶液浸润30 min。术前和术后5、15、40、100、150 d分别经耳缘静脉造影测量主动脉内径。术后5、15、150 d造影后每组分别处死4只兔作苏木精-伊红(HE)、弹力纤维EVG染色和免疫组化染色。结果实验组术后5 d均形成AAA,主动脉直径100 d内基本稳定,150 d时明显缩小;组织学上术后5 d血管壁严重破坏、结构紊乱,可见红细胞渗出和炎性细胞浸润,弹力纤维和平滑肌细胞明显减少甚至消失,15 d时血管结构规整,可见部分残留弹力纤维,未见炎性细胞,150 d时管腔变窄,内膜过度增生,可见大量平滑肌细胞增生和紊乱的新生弹力纤维。对照组均未见AAA形成,病理学无明显变化。结论国产猪胰弹性蛋白酶溶液浸泡法可诱导兔AAA形成,操作简单、安全、有效。该模型有自愈倾向,但100 d内基本稳定,有助于AAA机制研究。     

Aneurysmal sizing after endovascular repair in patients with abdominal aortic aneurysm: interobserver variability of various measurement protocols and its clinical relevance

The aim of this study was to determine the variability of various measurement protocols for measurement of abdominal aortic aneurysm (AAA) and the clinical relevance of variability. Three radiologists performed computed tomographic angiography measurements of both the aorta and the largest portion of the aneurysm on selected axial slices. Then measurements of the largest portion of the aneurysm were performed on unselected axial slices, sagittal and coronal reformatted. Finally, aortic volume was calculated. Measurements and volume calculation were performed before and after endovascular repair and assessed: Part 1: interobserver variability for maximum anteroposterior (MAP) and maximum transverse (MTR) diameters on selected slices; part 2: interobserver variability for unselected slices considering MAP and MTR; part 3: interobserver variability considering maximum diameter in any direction (MAD); part 4: interobserver variability for sagittal (SAG) and coronal (COR) free curved multiplanar reformation (MPR); and part 5: volume calculations. We then determined which technique of measurement was the most clinically relevant for detecting changes in aneurysm size or aortic volume. Parts 1 and 2: interobserver variability was 4.1 mm for both MAP and MTR; part 3: interobserver variability was 7 mm for MAD; part 4: interobserver variability was 5.5 mm (COR) and 4.9 mm (SAG); part 5: interobserver variability for volume was 5.5 ml. A combination of MAP and MTR was the most useful for detecting aortic modification. Volume calculation was needed in only a few cases. We recommend avoiding MAD and MPR measurements and suggest instead measuring both maximum anteroposterior and maximum transverse diameters. If aneurysm size remains stable after endovascular repair, aneurysm volume should be measured.     

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。     

Measurements before endovascular repair of abdominal aortic aneurysms. MR imaging with MRA vs. angiography and CT

Purpose:
1) To compare measurements obtained with MR imaging (MRI)/contrast-enhanced MR angiography (CE MRA) with measurements obtained with angiography (DSA) and CT, for stent-graft sizing of abdominal aortic aneurysms (AAA). 2) To compare MRA measurements obtained with the two post processing techniques MIP (maximum intensity projection) and VRT (3D volume rendering technique). Material and Methods:
The prospective study included 20 consecutive patients with AAA identified by DSA and CT as suitable for endovascular repair. For the study, MRI/CE MRA was performed. Five measurement variables for stent-graft sizing were chosen. Comparisons were made between MRI/CE MRA, DSA and CT, and between observers. Comparisons were also made between MIP and VRT. Results:
Significantly shorter lengths were obtained with MRA-MIP than with DSA. Three out of six diameter measurements were significantly smaller on MRI/CE MRA than on DSA and CT. No significant differences were found between the observers. One diameter measurement was significantly smaller on MIP than on VRT, while the other measurements showed no significant differences. Conclusion:
The length measurements obtained with MRA-MIP were probably more correct than those with DSA. For more reliable diameter measurements with CE MRA, improvements of the technique, including VRT reconstructions and a standardized determination of the vessel boundaries, are needed.     

Preoperative evaluation of abdominal aortic aneurysm by MR imaging with aortography correlation

Sonography, computed tomography, and most recently, magnetic resonance imaging (MRI) have been advocated as noninvasive imaging methods for the preoperative evaluation of patients with abdominal aortic aneurysms (AAA). We prospectively assessed the value of MRI in this clinical setying. Twenty of 23 patients with AAA referred for evaluation with biplane aortography underwent MRI within 3 days of aortography. MR and angiographic studies were interpreted prospectively and independently and then the results were compared with each other and with the operative findings. All angiographically demonstrated infrarenal and suprarenal aneurysms except one were documented as such by MRI. The distal extent of the aneurysm on MRI agreed with that on angiography in all but 3 cases. MRI is an accurate method for assessing the size and extent of AAA and its relationship to the main renal artery origins. MRI is not accurate in detecting vascular obstructions or accessory renal arteries. Therefore, the usefulness of MRI and the need for aortography in preoperative assessment of AAA depends upon the specific information the surgeon requires prior to aneurysmectomy in a given patient.     

An Animal Model of Abdominal Aortic Aneurysm Created with Peritoneal Patch: Technique and Initial Results

The purpose of this study was to develop an abdominal aortic aneurysm model that more closely resembles the morphology of human aneurysms with potential for further growth of the sac. An infrarenal abdominal aortic aneurysm (AAA) model was created with a double-layered peritoneal patch in 27 domestic swine. The patch, measuring in average from 6 to 12 cm in length and from 2 to 3 cm in width, was sutured to the edge of an aortotomy. Pre- and postsurgical digital subtraction aortograms (DSA) were obtained to document the appearance and dimensions of the aneurysm. All animals were followed with DSA for up to 5 months. Laparoscopic examination enhanced by the use of laparoscopic ultrasound was also carried out in 2 animals to assess the aneurysm at 30 and 60 days following surgery. Histological examination was performed on 4 animals. All the animals that underwent the surgical creation of the AAA survived the surgical procedure. Postsurgical DSA demonstrated the presence of the AAA in all animals, defined as more than 50% increase in diameter. The aneurysmal mean diameter increased from the baseline of 10.27 ± 1.24 to 16.69 ± 2.29 mm immediately after surgery, to 27.6 ± 6.59 mm at 14 days, 32.45 ± 8.76 mm at 30 days (p < 0.01), and subsequently decreased to 25.98 ± 3.75 mm at 60 days. A total of 15 animals died of aneurysmal rupture that occurred more frequently in the long aneurysms (6 cm in length) than the short aneurysms (<6 cm in length) during the first 2 weeks after surgery (p < 0.05). No rupture occurred beyond 16 days after surgery. Four animals survived and underwent 60-day angiographic follow-up. Laparoscopic follow-up showed strong pulses, a reddish external appearance and undetectable suture lines on the aneurysmal wall. On pathology, the patches were well incorporated into the aortic wall, the luminal wall appeared almost completely endothelialized, and cellular and matrix proliferation were noted in the aneurysmal wall. A reproducible technique for the creation of an infrarenal AAA model was developed using a peritoneal patch in swine. The aneurysm model proved to have potential for further growth of the sac and a tendency to rupture. Because of the growth potential, this might be a better model than those with a noncompliant aneurysmal wall for the preclinical evaluation of stent-graft devices.     

Hyperattenuating aortic wall on postmortem computed tomography (PMCT)

PURPOSE: To quantitatively evaluate the finding of hyperattenuating aortic wall on postmortem computed tomography (PMCT) and investigate its causes. MATERIALS AND METHODS: Our subjects were 50 PMCT of non-traumatic deaths and 50 CT of living persons (live CT). The ascending aorta at the level of the carina was visually assessed regarding the presence or absence of hyperattanuating aortic wall and hematocrit effect on PMCT and live CT. The diameter, thickness of the aortic wall, and CT number (HU) of the aortic wall and the lumen were also measured. RESULTS: Hyperattenuating aortic wall was detected in 100% of PMCT and 2% of live CT. The diameter of the aortic wall was 2.9 +/- 0.5 cm on PMCT and 3.5 +/- 0.5 cm on live CT, showing a significant difference. The thickness of the aortic wall was 2 mm on PMCT. Hematocrit effect was observed in 46% of PMCT and in none of live CT. With PMCT, there was a significant difference between the CT numbers of the upper and lower half portions of the lumen (19.6 +/- 11.7/30.9 +/- 12.9), whereas, with live CT, there was no such significant difference (37.4 +/- 7.6/38.9 +/- 6.7), with the overall value of 38.2 +/- 6.7. The CT number of the aortic wall was 49.9 +/- 10.9 on PMCT. CONCLUSION: The causes of hyperattenuating aortic wall on PMCT are considered to be increased attenuation due to contraction of the aortic wall, a lack of motion artifact, and decreased attenuation of the lumen due to dilution of blood after massive infusion at the time of cardiopulmonary resuscitation.     

High-resolution three-dimensional aortic magnetic resonance angiography and quantitative vessel wall characterization of different atherosclerotic stages in a rabbit model

PURPOSE: Atherosclerosis results in a considerable medical and socioeconomic impact on society. We sought to evaluate novel magnetic resonance imaging (MRI) angiography and vessel wall sequences to visualize and quantify different morphologic stages of atherosclerosis in a Watanabe hereditary hyperlipidemic (WHHL) rabbit model. MATERIAL AND METHODS: Aortic 3D steady-state free precession angiography and subrenal aortic 3D black-blood fast spin-echo vessel wall imaging pre- and post-Gadolinium (Gd) was performed in 14 WHHL rabbits (3 normal, 6 high-cholesterol diet, and 5 high-cholesterol diet plus endothelial denudation) on a commercial 1.5 T MR system. Angiographic lumen diameter, vessel wall thickness, signal-/contrast-to-noise analysis, total vessel area, lumen area, and vessel wall area were analyzed semiautomatically. RESULTS: Pre-Gd, both lumen and wall dimensions (total vessel area, lumen area, vessel wall area) of group 2 + 3 were significantly increased when compared with those of group 1 (all P < 0.01). Group 3 animals had significantly thicker vessel walls than groups 1 and 2 (P < 0.01), whereas angiographic lumen diameter was comparable among all groups. Post-Gd, only diseased animals of groups 2 + 3 showed a significant (>100%) signal-to-noise ratio and contrast-to-noise increase. CONCLUSIONS: A combination of novel 3D magnetic resonance angiography and high-resolution 3D vessel wall MRI enabled quantitative characterization of various atherosclerotic stages including positive arterial remodeling and Gd uptake in a WHHL rabbit model using a commercially available 1.5 T MRI system.     

Measurement of vessel wall strain using cine phase contrast MRI

PURPOSE: To determine the feasibility of using magnetic resonance imaging (MRI) to non-invasively measure strain in the aortic wall. MATERIALS AND METHODS: Cine phase contrast MRI was used to measure the velocity of the aortic wall and calculate changes in circumferential strain over the cardiac cycle. A deformable vessel phantom was used for initial testing and in vitro validation. Ultrasonic sonomicrometer crystals were attached to the vessel wall and used as a gold standard. RESULTS: In the in vitro validation, MRI-calculated wall displacements were within 0.02 mm of the sonomicrometer measurements when maximal displacement was 0.28 mm. The measured maximum strain in vitro was 0.02. The in vivo results were on the same order as prior results using ultrasound echo-tracking. CONCLUSION: Results of in vivo studies and measurement of cyclic strain in human thoracic and abdominal aortas demonstrate the feasibility of the technique.     

High-resolution magnetic resonance imaging at 2 Tesla: potential for atherosclerotic lesions exploration in the apolipoprotein E knockout mouse

INTRODUCTION: The aim of the present study was to evaluate the potential of high-resolution MRI at 2 Tesla (T) for direct noninvasive imaging of the aortic wall in a mouse model of atherosclerosis. MATERIAL AND METHODS: A specific mouse antenna was developed and sequence parameters were adjusted. T(1)- and T2-weighted images of abdominal aorta were obtained at 2 T with a spatial resolution of 86 x 86 x 800 microm3 in vivo. With a dedicated small coil, ex vivo MRI of the aorta was performed with a spatial resolution of 54 x 54 x 520 microm3. RESULTS: In vivo, the aortic wall was clearly defined on T(2)-weighted images in 15 of 16 mice: along the aorta the lumen circumference ranged from 1.07 to 3.61 mm and mean wall thickness from 0.11 to 0.67 mm. In vivo measurements of plaque distribution were confirmed by ex vivo MR imaging and by histology, with a good correlation with histology regarding lumen circumference (r = 0.94) and wall thickness (r = 0.97). CONCLUSION: Magnetic resonance imaging at 2 T to analyze in vivo atherosclerotic lesions in mice is possible with a spatial resolution of 86 x 86 x 800 microm3 and thus can be used for noninvasive follow-up in evaluation of new drugs.     

MSCT在腹主动脉瘤临床诊疗中的价值

目的：评估 MSCT在腹主动脉瘤(AAA)诊断和预后评价的价值。方法前瞻性收集本院经 MSCT 检查的26例疑似AAA患者,分析 MSCT检查的准确性和特点。结果26例患者经 MSCT诊断为 AAA,其中17例真性 AAA,9例假性 AAA。真性AAA的MSCT显示腹主动脉呈梭形扩张并向左前方膨出,瘤破裂患者残余瘤腔周围可见血栓和瘤壁钙化;假性AAA的MSCT显示腹主动脉旁偏心的膨大肿块,肿块可在血管钙化边界之外。手术诊断结果为25例 AAA,MSCT 与手术病理结果的符合率为96.1%(25/26);本组患者均出现动脉壁钙化的现象,其中17例伴有附壁血栓。结论 MSCT是一种安全、有效和无创性的诊断技术,对于AAA的早期发现,病情判断和指导治疗有较高的临床应用价值。     

The diagnostic value of anthropometric indices of maxillary sinuses for sex determination using CT-scan images in Iranian adults: A cross-sectional study

BackgroundThe identification of human remains is an essential part of forensic science. Studying paranasal sinuses is very useful in identification of mutilated or burnt bodies from accidents such as plane crashes. We aimed to assess the diagnostic value of anthropometric indices of maxillary sinuses for sex determination using CT-scan images in Iranian adults.MethodsCT-scan slices of 228 maxillary sinuses (from 144 men and 144 women) were studied. The maximum height, maximum anterior-posterior diameter, maximum width, and maximum distance between the sinuses were measured in both sexes. Our participants were divided into three age groups of 20–34, 35–49, and over 50 to compare the recorded measurements in different age groups.ResultsWe found a significant difference between men and women regarding the maximum height, maximum width, maximum A-P diameter of sinuses and the maximum distance between the right and left maxillary sinuses in all of our participants. We also found that the highest accuracy for sex determination was related to the maximum distance between the sinuses (65.6%) and the lowest to the maximum width of the right sinus (56.2%). The most accurate identification resulted from assessing the maximum distance between the sinuses in the 20–34 age group (74.3%), the maximum anterior-posterior diameter of the sinuses in the 35–49 age group (62.8%) and the maximum height of the left sinus in the over 50 age group (65.7%).ConclusionRegardless of age, according to our study the parameters of height, width, anterior-posterior diameter of sinuses and the maximum distance between the right and left maxillary sinuses are partially valuable for sex determination. The most accurate sex identification was examined in the 20–34 age group from studying the maximum distance between the sinuses. Especially in the over 50 age group, it is not enough to consider the sinus parameter for sex identification.     

Magnetic resonance imaging of aortic aneurysm

Magnetic resonance (MR) imaging in 16 patients with aortic aneurysm used a field of 5,000 Gauss and spin echo multisection imaging with two echos. Results were compared retrospectively with those of echotomography, computed tomography and angiography. Surgical exploration allowed correlation with histopathology in 13 patients. The external diameter of aneurysm and of its residual lumen and length of aneurysm were in each case evaluated precisely by MR. In patients with abdominal aneurysm, MR images identified the limits of the aneurysm in relation to renal and iliac arteries. In aneurysms of thoracic aorta, synchronization of signal with an ECG and longitudinal imaging provided data on relations of aneurysm with supraaortic trunks. In 2 patients with extensive, partially thrombosed thoracic and abdominal aorta aneurysm, MR imaging could not eliminate a diagnosis of aortic dissection with thrombosed false lumen. Finally, aortic wall calcifications were never apparent on MR images.     

腔内隔绝术治疗腹主动脉瘤(附2例报告)

目的：探讨腔内隔绝术治疗腹主动脉瘤（AAA）的方法、疗效、并发症及存在的问题。方法：2例高龄、多病并存的AAA患者在全订及动脉造影的监控下，植入血管内支架－聚酯移植物复合体，对AAA进行腔内隔绝术。结果：术后定期复查彩超、CT及血管造影显示支架通畅，无移位、扭曲、支架外壁与瘤腔间充满血栓，未发现搏动的肠系膜下动脉及腰动脉，未发现渗漏。AAA外径无变化。患者腹部搏动性肿块消失。结论：腔内隔绝术治疗AAA避免了外科手术的各种缺点，具有简便、安全、疗效确定等优点。     

Stanford B型主动脉夹层腔内修复术后早期死亡患者术前多层螺旋CT特征分析

目的探讨术前多层螺旋CT(MSCT)对Stanford B型主动脉夹层血管腔内修复术后早期死亡的预测价值。方法回顾性分析2014年1月至2018年12月采用腔内修复术治疗的158例急性期和亚急性期Stanford B型主动脉夹层患者临床随访资料和术前MSCT图像。测量和记录破口位置、破口大小、降主动脉最大直径、气管分叉平面主动脉直径、气管分叉平面假腔面积占该平面主动脉管腔总面积百分比、重要分支血管受累情况、假腔状态、腹主动脉是否受累等CT参数。分析术前CT各参数与患者术后30 d死亡的关系。结果腔内修复术紧急干预88例,非紧急干预70例,术后30 d死亡率为9.5%(15/158)。术后30 d死亡单因素分析显示,紧急干预患者术后30 d死亡率显著高于非紧急干预患者[13.6%(12/88)对4.3%(3/70),χ2=3.967,P=0.046];术后30 d死亡组患者气管分叉平面假腔面积占该平面主动脉管腔总面积≥50%患者[93.3%(14/15)对0.7%(1/143),χ2=135.581,P<0.001]和重要分支血管受累患者[66.7%(10/15)对32.9%(47/143),χ2=6.725,P=0.010]显著高于术后30 d生存组患者;两组患者破口位置、破口大小、降主动脉最大直径、气管分叉平面主动脉直径、假腔状态、腹主动脉是否受累比较,差异无统计学意义(P>0.05)。Logistic回归多因素分析显示,紧急干预(OR=1.31,95%CI=1.08~3.53,P=0.026)和气管分叉平面假腔面积占该平面主动脉管腔总面积≥50%(OR=9.53,95%CI=3.69~12.47,P<0.001)是Stanford B型主动脉夹层腔内修复术后30 d死亡的独立危险因素。结论术前MSCT对预测Stanford B型主动脉夹层腔内修复术后患者早期死亡具有重要价值,紧急干预和气管分叉平面假腔面积占主动脉管腔总面积≥50%是术后30 d死亡的独立危险因素。     

Platelet accumulation in abdominal aortic aneurysms and the effect of antiplatelet drugs: assessment by indium platelet scintigraphy]

A dual tracer technique using 111In labeled platelets and 99mTc labeled human serum albumin was applied to evaluate the in vivo thrombogenicity in 12 cases with abdominal aortic aneurysm (AAA) and the effect of antiplatelet drug on the thrombogenicity. The magnitude of platelet accumulation at AAA was expressed as the ratio of radioactivity of 111In platelets on the vascular wall to those in the blood pool (PAI; platelet accumulation index). Of the 12 patients with AAA, 11 had positive studies on baseline imaging and 1 had equivocally positive image. The PAI value (Mean +/- SD) over the AAA was 53.8 +/- 34.1% as compared to -8.6 +/- 4.4% in the control group (p less than 0.01). Seven patients with an AAA and positive baseline images were restudied during platelet active drug with 325 mg of aspirin. During treatment with aspirin, of 7 patients, 5 had positive images, of which 3 were decreased and others unchanged compared to baseline studies, 1 equivocally positive one and one negative one. The PAI value during treatment (21.9 +/- 18.6%) was significantly decreased compared to those in baseline study (52.1 +/- 23.9%). Our results suggest that the method used for platelet imaging in the present study may be useful for studying the in vivo thrombogenicity and the effect of platelet active drugs in AAA.     

Role of x-ray computed tomography in the preoperative evaluation of aneurysm of the abdominal aorta

The authors have studied the files of 50 consecutive patients (1987-89) operated for abdominal aortic aneurysm (AAA) and examined with CT. The criteria for inclusion were surgical features. CT can be made more accurate for the study of AAA: Thus the location of the neck of the aneurysm relative to the renal arteries was defined in 94% of all cases. In addition, CT yields information about the wall of the aneurysm, whether it be thickened (3 inflammatory aneurysms were properly diagnosed) or, mor importantly, weakened (solution of continuity in the wall in the "prior-to-rupture" appearance). Owing to the quality of its performances and to its noninvasive character, the authors regard CT with contrast injection as an essential technique for the preoperative assessment of abdominal aortic aneurysm in most cases. The examination must be carried out strictly, especially for the contiguous sections of the renal arteries and their extension to the crural arch. As it demonstrates weakened areas more easily, a more accurate study of the aneurysmal wall with CT might increase the surgical indications for some smaller aneurysms, the potential evolution of which does not seem to be associated with their diameter only.     

Automatic vessel wall contour detection and quantification of wall thickness in in-vivo MR images of the human aorta

PURPOSE: To develop an automated technique to trace the contours of the lumen and outer boundary of the aortic wall, and measure aortic wall thickness in axial MR images. MATERIALS AND METHODS: The algorithm uses prior knowledge of vessel wall morphology. A geometrical model (ellipse) is deformed, translated and rotated to obtain a rough approximation of the contours. Model-matching is based on image gradient measurements. To enhance edges, the images were preprocessed using gray-level stretching. Refinement is performed by means of dynamic programming. Wall thickness is computed by measuring the distance between inner and outer contour of the aortic wall. RESULTS: The algorithm has been tested on high-resolution axial MR images from 28 human subjects of the descending thoracic aorta. The results demonstrate: High correspondence between automatic and manual area measurements: lumen (r = 0.99), outer (r = 0.96), and wall thickness (r = 0.85). CONCLUSION: Though further optimization is required, our algorithm is a powerful tool to automatically draw the boundaries of the aortic wall and measure aortic wall thickness in aortic wall devoid of major lesions. J. Magn. Reson. Imaging 2006. (c) 2006 Wiley-Liss, Inc.     

Gradient Echo MRI Characterization of Development of Atherosclerosis in the Abdominal Aorta in Watanabe Heritable Hyperlipidemic Rabbits

Purpose The Watanabe Heritable Hyperlipidemic (WHHL) rabbit provides an important model of spontaneous atherosclerosis. With a strain of WHHL rabbits which do not develop abdominal aorta lumen stenosis even with advanced atherosclerosis, we studied the MRI–histology correlation, and the natural progression of atherosclerosis in the abdominal aorta. In addition, intra-reader segmentation repeatability and scan–rescan reproducibility were assessed. Methods Two batches of female WHHL rabbits were used. The first batch of 6 rabbits was scanned at 20 weeks old. A second batch of 17 rabbits was scanned at 50 weeks old and then randomly divided into two subgroups: 8 were killed for histologic investigation; 9 were kept alive for follow-up, with repeat scanning a week later to assess scan–rescan reproducibility, and again at 73 weeks old to assess disease progression. MR images were acquired at 4.7 T using a chemical shift selective fat suppression gradient echo with a saturation band suppressing blood signal within the aortic lumen. Five slices per animal were acquired, centered around the renal artery region of the abdominal aorta, with in-plane resolution of 0.195 mm and slice thickness of 3 mm. Results The coefficient of variation for intra-reader reproducibility for aortic wall thickness measurements was 2.5% for repeat segmentations of the same scans on the same day, but segmentations of these same scans made 8 months later showed a systematic change, suggesting that intra-reader bias as well as increased variability could compromise assessments made over time. Comparative analyses were therefore performed in one postprocessing session. The coefficient of variation for scan–rescan reproducibility for aortic wall thickness was 5.5% for nine pairs of scans acquired a week apart and segmented on the same day. Good MRI–histology correlation was obtained. The MRI-measured mean aortic wall thickness of animals at 20 weeks of age was 76% that of animals at 50 weeks of age (p < 0.001). There was a small increase in aortic wall thickness between 50 and 73 weeks of age, but this was not significant (p > 0.05). The corresponding differences in lumen cross-sectional areas at 20, 50, and 73 weeks of age were not significant. These results were consistent with in-house historical histology data on this strain of rabbits. Conclusions High-resolution gradient echo MRI can follow disease progression in the WHHL rabbit spontaneous atherosclerosis disease model.