High-resolution 3D arteriography of chronic total peripheral occlusions using a T1-W turbo spin-echo sequence with inner-volume imaging

Abstract

Percutaneous revascularization of peripheral artery chronic total occlusion (CTO) is challenging under X-ray guidance without direct image feedback, due to poor visualization of the obstructed segment and underappreciation of vessel tortuosity. Operators are required to steer interventional devices relatively "blindly," and therefore procedural failure or perforation may occur. Alternatively, MRI may allow complete visualization of both patent and occluded arterial segments. We designed and implemented a 3D high-resolution, T(1)-weighted (T(1)-W) turbo spin-echo (TSE) MRI sequence with inner-volume (IV) imaging to enable detailed peripheral artery CTO imaging. Using this sequence, high-resolution volumes of interest (VOIs) around the vessel were achieved within 5-10 min. This imaging approach may be used for rapid pre- and postprocedural evaluations, and as a 3D roadmap that can be overlaid during real-time X-, MR-, or XMR-guided catheterization. Experiments were successfully performed on a carotid CTO model in swine ex vivo, and in peripheral arteries in normal volunteers and patients in vivo. Delineation of the vascular architecture, including contrast differences between the patent and occluded artery segments, and lesion morphology heterogeneity were visualized.

Figures

FIG. 1

a: X-ray angiogram of a patient with a totally occluded left common iliac artery at its origin at the aortic bifurcation. The black box overlaid on the image indicates the orientation of the IV. b: The readout, phase-encode, and partition directions are indicated by arrows.

FIG. 2

Pulse sequence diagram depicting the IV-TSE sequence.

FIG. 3

a: Phantom image acquired using the IV-TSE sequence. b: Slice profile along the phase-encoding direction for the cross-sectional slice indicated by the dashed white line in a. The prescribed slab thickness was 24 mm (see solid vertical lines in b). The actual FOV acquired was 36 mm (see dot-dashed vertical lines in b).

FIG. 4

a: Sagittal slice of the chronically occluded carotid artery from a porcine model. b: Comparison of the IV-MR images with histology-stained images (VVG and MT) in three representative axial slices pre-bifurcation, at the bifurcation, and just post-bifurcation. The positions of these slices are indicated by blue lines in a. The scale corresponds to the histology-stained photographs. Note the common carotid bifurcating into the patent right carotid artery and the occluded left carotid artery in b-3. Note also the whitish appearance of the loose collagenous matrix (b-2), the light grayish appearance of the collagenous adventitia (b-3), and the dark gray appearance of the media (b-1). Plaque features are reproduced in the IV-TSE images (small blue arrows).

FIG. 5

a: Sagittal slice of the occluded left carotid artery. b: Comparison of the IV-MR images with histology-stained images (VVG and MT) in six representative axial slices throughout the length of a chronically occluded carotid artery from a porcine model. The positions of these slices are indicated by blue lines in a. The scale corresponds to the histology-stained photographs. Note the dark gray to black appearance of plaque calcification (blue arrows in b-1,2). Medial rupture is also reproduced within the resolution limitations of the sequence (blue arrows in b-3).

FIG. 6

IV-TSE images obtained from normal volunteers. a: A sagittal slice of a SFA in a normal volunteer. b: A sagittal slice and (c) five axial slices at positions marked by the white lines in (a) from a popliteal artery in a normal volunteer. Note the good black-blood suppression in both arteries. Note also incomplete suppression of the slow-moving blood in the popliteal vein in b and c. The vessel wall boundary is marked by the dotted line overlaid in images a and b.

FIG. 7

a: A sagittal slice in the same orientation as Fig. 1a, depicting the bifurcation and the intraluminal lesion. b: A series of 18 axial images from a patient with a CTO in the left iliac artery just distal to the bifurcation (see X-ray image of this patient in Fig. 1). Note the lumen occlusion beginning at axial slices 5 and 6, and extending up to slice 16. The in-plane resolution is 0.8 mm × 0.8 mm. The positions of the proximal (S1) and distal (S18) slices are marked on the sagittal slice in a by white lines.

FIG. 8

a: MR angiogram of a patient with chronic PAD in both legs. Specifically, note the completely occluded left SFA below the first dashed black line, and the presence of increased collateral circulation to partially compensate for the low perfusion. b: A series of 25 axial slices of the left leg spaced every 4 mm. The positions of the first and last images in the series are shown by the two dashed black lines in Fig. 7a. The white boxes highlight the position of the left SFA. The images clearly depict spatial variations in the plaque structure, such as medial hypertrophy (arrow 1), fibrous plaque bridges (arrow 2), and finger-like structures extending from one end of the wall (arrow 3). Compositional variations (arrows 4 and 5) are also apparent in these images.

FIG. 9

a: MR angiogram of the iliac artery structure obtained from a MIP of a 3D TOF imaging sequence. Note the CTOs in the descending aorta and the common iliac arteries around the bifurcation. The common iliacs are reconstituted further along. b: A reconstructed curved slice passing through the center of the aorta and left common iliac artery from the IV-TSE imaged volume is shown. The white box in a depicts the approximate position of the imaged FOV. The black line overlaid on the image depicts the borders of the artery. The occluded and patent segments of the artery are clearly visible in this curved slice image, giving it an angiogram-like appearance.

FIG. 10

A comparison of four representative high-resolution (0.5 mm × 0.5 mm) full-FOV axial slices obtained from a 2D T1-WTSE sequence (left column) with reconstructed slices obtained from a reduced FOV IV-TSE volume (right column) at the closest corresponding locations in a patient with a CTO in the SFA. The white boxes indicate the approximate position and size of the IV FOV, and the black arrows in all the images point to the SFA. Note the good correlation in the images.

FIG. 11

a: MR angiogram of the iliac artery structure obtained from an MIP of a 3D TOF imaging sequence. b: A series of 24 axial slices reconstructed from the IV TSE acquisition of the left external iliac artery. The positions of the first and last images in the series are shown by the two solid white lines in a. Note the gradual progression of the completely occluded lumen to the partially open lumen across the images.