- Oral presentation
- Open Access
Phase-sensitive black-blood coronary vessel wall imaging
Journal of Cardiovascular Magnetic Resonancevolume 11, Article number: O11 (2009)
Black-blood coronary vessel wall imaging is a powerful non-invasive tool for the quantitative assessment of positive arterial remodeling . Although dual-inversion-recovery  (DIR) is the gold standard for vessel wall imaging, optimal lumen-vessel wall contrast is sometimes difficult to obtain and the time-window available for imaging is limited due to the competing requirements between TI* (blood signal nulling time) and TD (period of minimal myocardial motion). In addition, atherosclerosis is a spatially heterogeneous disease and therefore imaging at multiple anatomical levels of the coronary circulation is mandatory. However, this requirement of enhanced volumetric coverage typically comes at the expense of increased scanning time. Phase-sensitive IR [3–5] (PS-IR) has shown to be valuable for enhancing tissue-tissue contrast and for making IR imaging less sensitive to TI*. This work extends PS-IR to PS-DIR and combined with spiral-imaging, multi-slice black-blood coronary vessel wall imaging is enabled in a single breath-hold.
To develop, and test a phase-sensitive DIR (PS-DIR) single-breath-hold multi-slice spiral black-blood coronary vessel wall imaging method.
After DIR (Fig. 1), the inversion time TI* allows for signal-nulling of the in-flowing blood-pool at the anatomical level of interest. Blood-tissue contrast therefore depends on the accurate determination of TI*. Although the MR signal is complex (magnitude and phase), DIR images only show the magnitude of the signal with a suboptimal blood-tissue contrast if TI does not equal TI*. However, by additionally using the MR signal phase, a signed (positive/negative) black-blood image can be acquired at TI less than TI* and reconstructed with a blood-tissue contrast higher than that obtained at TI*. Simultaneously, competing constraints related to TI* and TD are avoided (Fig. 1). Consequently, single-breath-hold multi-slice black-blood coronary vessel wall imaging is enabled using PS-DIR.
A local region-growing reconstruction algorithm was developed and is summarized in Fig. 2. Pixels with high signal near the cross-sectional coronary artery are selected as seed points. The phase values of these points are used to estimate the local signal phase inhomogeneity which is needed for local signed-magnitude image reconstruction .
A single breathhold DIR sequence was implemented (Fig. 1) on a clinical 3 T Philips-Achieva MRI-system. Data were acquired using a segmented k-space spiral acquisition with spectral spatial excitation . Image processing was performed off-line on a personal computer.
Anatomical slices perpendicular to the proximal part of the right coronary artery (RCA) at end-systole were planned similar to a previously published methodology . First, serial single-slice multi-phase PS-DIR images were acquired with incremental TI ranging from 50 ms–500 ms in 15 healthy adult subjects (slice-thickness = 8 mm, FOV = 190 × 190 mm, matrix = 320 × 320, interleaves = 20, acq.window = 18 ms/interleaf). CNR was calculated on the signed-magnitude images reconstructed with the above algorithm. Mean vessel wall thickness was measured manually on the images obtained with incremental TI and was compared to that from TI*. Finally, a dual-slice rather than a multi-phase version of the sequence (Fig. 1) was tested in four subjects.
Using TI less than TI*, Fig. 3 shows that PS-DIR enables delineation of the coronary artery vessel wall and supports an increased wall-lumen contrast when compared with the conventional DIR in which TI was too short for adequate blood signal-nulling. Consistent with the visual findings, Fig. 4 shows that the CNR significantly increased in PS-DIR over a broad range of TI (150 ms–300 ms). Wall thickness measurements using PS-DIR at different TI values were consistent with those from DIR at TI*. Since the PS-DIR method permits image data collection over a broad range of TI (Fig. 4), multiple slices rather than multiple phases can be obtained at no extra cost in scanning time (Fig 5).
PS-DIR provides a TI-insensitive higher CNR alternative to conventional DIR for coronary vessel wall imaging. TI-insensitivity can be traded for enhanced volumetric coverage at no extra-cost in imaging time.
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