Whole‐heart, ungated, free‐breathing, cardiac‐phase‐resolved myocardial perfusion MRI by using Continuous Radial Interleaved simultaneous Multi‐slice acquisitions at sPoiled steady‐state (CRIMP)

Abstract

Purpose To develop a whole‐heart, free‐breathing, non‐electrocardiograph (ECG)‐gated, cardiac‐phase‐resolved myocardial perfusion MRI framework (CRIMP; Continuous Radial Interleaved simultaneous Multi‐slice acquisitions at sPoiled steady‐state) and test its quantification feasibility. Methods CRIMP used interleaved radial simultaneous multi‐slice (SMS) slice groups to cover the whole heart in 9 or 12 short‐axis slices. The sequence continuously acquired data without magnetization preparation, ECG gating or breath‐holding, and captured multiple cardiac phases. Images were reconstructed by a motion‐compensated patch‐based locally low‐rank reconstruction. Bloch simulations were performed to study the signal‐to‐noise ratio/contrast‐to‐noise ratio (SNR/CNR) for CRIMP and to study the steady‐state signal under motion. Seven patients were scanned with CRIMP at stress and rest to develop the sequence. One human and two dogs were scanned at rest with a dual‐bolus method to test the quantification feasibility of CRIMP. The dual‐bolus scans were performed using both CRIMP and an ungated radial SMS saturation recovery (SMS‐SR) sequence with injection dose = 0.075 mmol/kg to compare the sequences in terms of SNR, cardiac phase resolution and quantitative myocardial blood flow (MBF). Results Perfusion images with multiple cardiac phases in all image slices with a temporal resolution of 72 ms/frame were obtained. Simulations and in‐vivo acquisitions showed CRIMP kept the inner slices in steady‐state regardless of motion. CRIMP outperformed SMS‐SR in slice coverage (9 over 6), SNR (mean 20% improvement), and provided cardiac phase resolution. CRIMP and SMS‐SR sequences provided comparable MBF values (rest systolic CRIMP = 0.58 ± 0.07, SMS‐SR = 0.61 ± 0.16). Conclusion CRIMP allows for whole‐heart, cardiac‐phase‐resolved myocardial perfusion images without ECG‐gating or breath‐holding. The sequence can provide MBF if an accurate arterial input function is obtained separately.

High spatial resolution spiral first‐pass myocardial perfusion imaging with whole‐heart coverage at 3 T

“…Recent studies using Cartesian and radial imaging at 3T have either demonstrated lower spatial-temporal resolution or more limited spatial coverage than what is feasible using spiral trajectories. [19][20][21] The enhanced spatial resolution may increase the ability to assess transmural differences in myocardial perfusion, [24][25][26] and the whole-heart coverage may improve the ability to assess the extent of ischemia and quantify the ischemic burden.…”

“…Recent radial and Cartesian perfusion studies at 3T have used an in-plane resolution of around 1.5-2 mm. [19][20][21][22][23] However, with higher spatial resolution there is increased ability to detect transmural perfusion differences between the epicardium and the endocardium, which could improve the ability to detecting obstructive CAD as demonstrated in prior studies. [24][25][26][27] Recent advance in high-resolution SMS Cartesian perfusion imaging using balanced steady-state free precession (bSSFP) provides another possibility for high-resolution perfusion imaging.…”

“…Overall, whole‐heart coverage with an in‐plane spatial resolution of 2 × 2 mm 2 were achieved at 1.5T scanners using the aforementioned spiral perfusion techniques. Recent radial and Cartesian perfusion studies at 3T have used an in‐plane resolution of around 1.5‐2 mm 19‐23 . However, with higher spatial resolution there is increased ability to detect transmural perfusion differences between the epicardium and the endocardium, which could improve the ability to detecting obstructive CAD as demonstrated in prior studies 24‐27 .…”

Improved simultaneous multislice cardiac MRI using readout concatenated k‐space SPIRiT (ROCK‐SPIRiT)

“…8 Multiple studies have explored the use of SMS imaging in CMR for faster coverage. [9][10][11][12][13][14][15][16][17][18][19][20][21][22] In particular, SMS acceleration has been used for myocardial T 1 mapping, 13,18 for cine imaging, 16,21 and for perfusion imaging 11,14,15,17,22 using both Cartesian and non-Cartesian acquisitions at different acceleration rates. However, due to coil geometry limitations, SMS acceleration remains limited for CMR, especially in conjunction with in-plane parallel imaging, in which leakage artifacts and noise amplification are observed at high acceleration rates, 23 necessitating improvements in reconstruction.…”

“…Simultaneous multislice imaging is typically coupled with controlled aliasing, to further increase dissimilarities among the coil profiles across the slices and to reduce g‐factor noise amplification 8 . Multiple studies have explored the use of SMS imaging in CMR for faster coverage 9‐22 . In particular, SMS acceleration has been used for myocardial T 1 mapping, 13,18 for cine imaging, 16,21 and for perfusion imaging 11,14,15,17,22 using both Cartesian and non‐Cartesian acquisitions at different acceleration rates.…”