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Initial Clinical Evaluation of Quantitative Ultra-high Resolution First-pass Spiral Perfusion Imaging with Whole Heart Coverage in Patients with Ischemic Heart Disease at 3T

Yang Yang¹, Austin Robinson¹, Roshin Mathew¹, Christopher M Kramer^1,2, and Michael Salerno^1,2,3

¹Medicine, University of Virginia, Charlottesville, VA, United States, ²Radiology, University of Virginia, Charlottesville, VA, United States, ³Biomedical Engineering, University of Virginia, Charlottesville, VA, United States

Synopsis

First-pass contrast-enhanced myocardial perfusion imaging is a useful noninvasive tool to evaluate patients with coronary artery disease, but current techniques are still limited in spatial-temporal resolution, ventricular coverage and absolute quantification which reduces the sensitivity to detect perfusion differences between the endocardium and epicardium and quantify ischemic burden. In this study, we designed a dual-density dual-contrast spiral pulse sequence to achieve quantitative ultra-high resolution first-pass spiral perfusion imaging with whole heart coverage at 3T and further tested in 9 patients with suspected CAD undergoing cardiac catheterization.

Introduction

Adenosine stress perfusion cardiac magnetic resonance (CMR) imaging is an important clinical tool to diagnose coronary artery disease (CAD) and may be superior to nuclear myocardial perfusion imaging¹. Current clinical available CMR myocardial perfusion imaging has limited spatial coverage of the left ventricle and relatively low spatial resolution (2-2.3mm)². Quantitative myocardial perfusion detects a greater burden of ischemia in subjects with multi-vessel CAD as compared to visual analysis and will play an increasingly important role for assessing the need for revascularization³. We have previously demonstrated the feasibility of performing perfusion imaging ultra-high spatial resolution of 1.25 mm with whole heart coverage using dual density spiral trajectories at 3T⁴. In this study, we further extend it to dual contrast quantitative sequence and demonstrate the preliminary clinical application of quantitative ultra-high resolution first-pass spiral perfusion imaging with whole heart coverage in nine patients with suspected CAD who were scheduled to undergo cardiac catheterization.

Methods

Our previous interleaved high-resolution spiral pulse sequence was modified to a dual contrast sequence by acquiring proton density (PD) and AIF images to enable quantification of myocardial perfusion as shown in Fig. 1. PD images were collected in the first four heart beats utilizing a 5 degree flip angle (FA) and no saturation pulse. Data was collected using a dual density spiral perfusion technique described previously. The spiral trajectory was designed as 4 interleaves with 4ms per interleave, 20% of trajectory fully sampled with ending density of 0.05x Nyquist. Other sequence parameters included: FOV 340mm, TE 1.0ms, TR 7ms, SRT 90ms, FA 26^o, 6 slices with 10mm thickness. AIF images were acquired with a 2x accelerated single-shot spiral acquisition using a 45^o FA with the following parameters: in-plane resolution 6.95mm, SRT 10ms. Adenosine stress CMR was performed in nine patients scheduled to undergo cardiac catheterization for evaluation of CAD. Perfusion images were acquired on a 3T Prisma Siemens Scanner during injection of 0.075mmol/kg of Dotarem contrast bolus. First-pass stress imaging was performed following a 3-minute infusion of adenosine (140mcg/kg/min). The images were reconstructed by L1-SPIRiT⁵ using finite temporal difference as the sparsity transform. Myocardial blood flow was performed on a pixel-wise basis using Fermi-function deconvolution in a custom MATLAB program. Endocardial to epicardial (Endo:Epi) ratios were calculated as the ratio of myocardial blood flow (MBF) in the endocardium of each segment divided by the MBF of the epicardium in the same segment.

Results

Table 1 summarized the patient characteristics of the subjects included in the study. Among the enrolled patients, 6 had severe stenosis or chronic occlusions of major epicardial coronary arteries and 3 had non-obstructive CAD. Fig. 2 showed the stress (a) and rest (b) myocardial perfusion images from a representative patient demonstrating stress-induced reductions in myocardial perfusion in the anterior, antero-septal and infero-septal segments (yellow arrows). Quantitative myocardial blood flow map in Fig. 2 (c) and (d) as well as the bull-eye segmental MBF in Fig. 2 (e) and (f) confirmed stress-induced reductions of perfusion in corresponding territories. Endo:Epi ratios were 0.48, 0.29 and 0.64 in the anterior, antero-septal, and infero-septal segments, respectively, compared to 0.83, 0.81, and 0.77 in the inferior, infero-lateral and antero-lateral segments. Late gadolinium enhancement (LGE) imaging in Fig. 3 (a) showed no scar in this patient. Invasive quantitative coronary angiography (QCA) revealed subtotal occlusion of the ostial left anterior descending artery in Fig. 3(b). Eight out of nine patients have absolute quantitative CMR perfusion measurement. Fig. 4 showed all eight patients’ MBF Endo:Epi at stress (a) and rest (b) at all three main vessel territories: left anterior descending artery (LAD), right coronary artery (RCA) and left circumflex artery (LCx). The presence of a stress MBF Endo:Epi <0.6 in at least one segment differentiates CAD patients with severe stenosis or chronic occlusions from patients with non-obstructive CAD (PT#2, #4 and #9).

Discussion

Dual-density, dual-contrast spiral sequence generated high quality perfusion images of high SNR and ultra-high spatial resolution (1.25mm) with whole heart coverage thus making them ideal for perfusion imaging and pixel-wise absolute quantification of perfusion. In patients with CAD there is good correlation between the regions of reduced stress perfusion, the visual perfusion defects, and the location of obstructive CAD at cardiac catheterization. In this initial clinical evaluation, the stress MBF Endo:Epi ratio may be a useful marker to differentiate CAD patient with severe stenosis or chronic occlusions from non-obstructive CAD patients.

Conclusion

We demonstrate that quantitative ultra-high resolution adenosine stress perfusion imaging with whole heart coverage at 3T is feasible with spiral-based dual-density dual-contrast perfusion techniques with good regional correlation with cardiac catheterization.

Acknowledgements

This work was supported by NIH R01 HL131919 and T32 EB003841.

References

1. Schwitter J, Wacker CM, Wilke N, Al-Saadi N, Sauer E, Huettle K, Schonberg SO, Luchner A, Strohm O, Ahlstrom H et al. 2013. Mr-impact ii: Magnetic resonance imaging for myocardial perfusion assessment in coronary artery disease trial: Perfusion-cardiac magnetic resonance vs. Single-photon emission computed tomography for the detection of coronary artery disease: A comparative multicentre, multivendor trial. Eur Heart J. 34(10):775-781.

2. Kellman P, Arai AE. 2007. Imaging sequences for first pass perfusion --a review. J Cardiovasc Magn Reson. 9(3):525-537.

3. Patel AR, Antkowiak PF, Nandalur KR, West AM, Salerno M, Arora V, Christopher J, Epstein FH, Kramer CM. 2010. Assessment of advanced coronary artery disease: Advantages of quantitative cardiac magnetic resonance perfusion analysis. J Am Coll Cardiol. 56(7):561-569.

4. Yang Y, Van Houten M, Kramer CM, Salerno M. 2017. Ultra-high spatial resolution spiral myocardial perfusion imaging with whole heart coverage at 3T. 2018 SCMR/ISMRM workshop.

5. Yang Y, Kramer CM, Shaw PW, Meyer CH, Salerno M. 2015. First-pass myocardial perfusion imaging with whole-heart coverage using l1-spirit accelerated variable density spiral trajectories. Magn Reson Med.

Figures

Figure 1: Pulse sequence schematics of proposed dual-density dual-contrast ultra-high resolution first-pass spiral perfusion imaging with whole heart coverage. At each saturation recovery block, following the pulse train, a single shot spiral is applied at shorter TS to acquire low spatial resolution arterial input function image. Fat suppression pulse is utilized and then followed by interleaved spiral imaging at two slice locations. Each slice is sampled by 4 interleaved spirals each with a TR of 7 ms. Due to the slice interleaving, the effective temporal resolution of each slice is 7*TR (49 ms), and the TS times differ by 1 TR (7 ms).

Figure 2: Stress (a) and rest (b) myocardial perfusion images from a representative patient demonstrating stress-induced reductions in myocardial perfusion in the anterior, antero-septal and infero-septal segments (yellow arrows). Quantitative myocardial blood flow map at stress (c) and rest (d) as well as the bull-eye segmental MBF at stress (e) and rest (f) confirmed stress-induced reductions of perfusion in corresponding territories.

Figure 3: (a) Late gadolinium enhancement (LGE) imaging showed no scar in the same patient. Invasive quantitative coronary angiography (QCA) revealed subtotal occlusion of the ostial left anterior descending artery in (b).

Figure 4: Eight patients’ MBF Endo:Epi ratio at stress (a) and rest (b) from all three main vessel territories: left anterior descending artery (LAD), right coronary artery (RCA) and left circumflex artery (LCx). The presence of a stress MBF Endo:Epi <0.6 in at least one segment would differentiate CAD patient with severe stenosis or chronic occlusions from patients with non-obstructive CAD (PT#2, #4 and #9).

Table 1: Demographic Data and Patient Characteristics

Proc. Intl. Soc. Mag. Reson. Med. 27 (2019)

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