Isotropic 3D black blood MRI of abdominal aortic aneurysm wall and intraluminal thrombus

Abstract

Introduction The aortic wall and intraluminal thrombus (ILT) have been increasingly studied as potential markers of progressive disease with abdominal aortic aneurysms (AAAs). Our goal was to develop a high resolution, 3D black blood MR technique for AAA wall and ILT imaging within a clinically acceptable scan time. Methods Twenty two patients with AAAs (maximal diameter 4.3±1.0cm), along with five healthy volunteers, were imaged at 3T with a 3D T1-weighted fast-spin-echo sequence using variable flip angle trains (SPACE) with a preparation pulse (DANTE) for suppressing blood signal. Volunteers and ten patients were also scanned with SPACE alone for comparison purposes. The signal to noise ratio (SNR) and the aortic wall/ILT to lumen contrast to noise ratio (CNR) were measured. Qualitative image scores (1–4 scale) assessing the inner lumen and outer wall boundaries of AAA were performed by two blinded reviewers. In patients with ILT, the ratio of ILT signal intensity (ILTSI) over psoas muscle SI (MuscleSI) was calculated, and the signal heterogeneity of ILT was quantified as standard deviation (SD) over the mean. Results All subjects were imaged successfully with an average scan time of 7.8±0.7 minutes. The DANTE preparation pulse for blood suppression substantially reduced flow artifacts in SPACE with lower lumen SNR (8.8 vs. 21.4, p<0.001) and improved the wall/ILT to lumen CNR (9.9 vs. 6.3, p<0.001) in patients. Qualitative assessment showed improved visualization of lumen boundaries (73% higher scores on average, p=0.01) and comparable visualization of outer wall boundary (p>0.05). ILT was present in ten patients, with relatively high signal and a wide SD (average ILTSI/MuscleSI 1.42±0.48 (range 0.75–2.11) ) and with SD/mean of 27.7%±6.6% (range 19.6% – 39.4%). Conclusion High resolution, 3D black blood MRI of AAAs can be achieved in a clinical accepted scan time with reduction of flow artifacts using the DANTE preparation pulse. Signal characteristics of ILT can be quantified and may be used for improved patient-specific risk stratification.

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

“…To account for the real flow characteristics in deep veins, we chose to optimize DANTE parameters through in-vivo studies. In order to simplify the parameter optimization process, the duration (0.9 ms) and strength (20 mT/m) of gradient pulses and RF pulse flip angle (15°) were kept fixed, which are within a range typically reported in literature [21, 23–26]. Thus, PTL was the only parameter to be optimized in the following healthy volunteer study.…”

Segmentation of lumen and outer wall of abdominal aortic aneurysms from 3D black-blood MRI with a registration based geodesic active contour model

“…Since the Signal-to-Noise Ratio (SNR) from black-blood MR images of AAA is high (Zhu et al, 2016), in the present study we only use the image processing function to enhance the contrast level. The global contrast enhanced filter applied the same level of enhancement for all CE-MRA images for both lumen segmentation and on the filled images (shown in Fig.…”

“…That study proposed a semi-automated algorithm to jointly segment the lumen and outer wall from 3D femoral artery black-blood MRI. To the best of our knowledge, the work from our group (Zhu et al, 2016) was the first study evaluating 3D black-blood MRI techniques in patients with AAA disease. This report is the first to investigate segmentation of the AAA lumen and outer wall using 3D black-blood MR images.…”

Non-contrast 3D black blood MRI for abdominal aortic aneurysm surveillance: comparison with CT angiography

“…A 3D T 1 weighted black blood sequence (fast-spin-echo with variable refocusing flip angle train, SPACE) with blood suppression preparation (DANTE) [18] as developed by our group was acquired in the coronal plane covering the abdominal aorta from the renal arteries to the aortic bifurcation [17]. Acquisition parameters were as follows: TR/TE = 800 ms/20 ms; 32 × 32-cm 2 field of view (FOV); 52 coronal slices; echo train length 60; resolution was 1.3 mm isotropic with a scan time of 7 minutes (during free breathing).…”

“…As the composition of ILT is poorly visualized on CT, MRI could provide unique insight by better characterizing ILT. Most publications that describe the use of MRI for AAA evaluation have limited coverage and coarse through-plane resolution (4–5 mm) [5, 15, 16] We recently developed a 3D black blood non-contrast MRI technique that allows high-resolution (1.3 mm) isotropic imaging of the lumen and wall with evaluation of ILT composition within a clinically acceptable time (7 minutes) [17]…”