First-pass Perfusion Magnetic Resonance Imaging Research Articles

Novel implementation of cardiac magnetic resonance first-pass perfusion imaging for semi-quantitatively evaluating microvascular dysfunction in paediatric patients with Duchenne muscular dystrophy.

The current study aimed to assess myocardial microcirculation dysfunction via cardiac magnetic resonance (CMR) first-pass perfusion imaging in children with Duchenne muscular dystrophy (DMD). In total, 67 children with DMD and 15 controls who underwent contrast-enhanced CMR first-pass perfusion imaging were enrolled in this study. CMR first-pass perfusion and late gadolinium enhancement (LGE) sequences were acquired. Further, the global, regional, and coronary artery distribution area perfusion indexes (PI), upslope (%BL), maximum signal intensity (MaxSI), time to maximum signal intensity (TTM), and baseline SI were analysed. The perfusion parameters of the LGE positive (+), LGE negative (-), and control groups were compared. Pearson correlation analysis was performed to assess the association between myocardial microcirculation and conventional cardiac function and LGE parameters. The LGE+ group had a significantly lower global and apical-ventricular MaxSI than the control group (all P < .05). The left anterior descending arterial (LAD), left circumflex coronary arterial (LCX), and right coronary arterial (RCA) segments of the LGE+ group had a lower upslope and MaxSI than those of the control group (all P < .05). The LAD segments of the LGE- group had a lower MaxSI than those of the control group (41.10 ± 11.08 vs 46.36 ± 13.04; P < .001). The LCX segments of the LGE- group had a lower PI and upslope than those of the control group (11.05 ± 2.84 vs 12.46 ± 2.82; P = .001; 59.31 ± 26.76 vs 68.57 ± 29.99; P = .002). Based on the correlation analysis, the upslope, MaxSI, and TTM were correlated with conventional cardiac function and LGE extent. Paediatric patients with DMD may present with microvascular dysfunction. This condition may appear before LGE and may be correlated with coronary artery blood supply and LGE extent. First-pass perfusion parameters may reveal the status of myocardial microcirculation and reflect the degree of myocardial injury at an earlier time in DMD patients. Perfusion parameters should be analysed not only via global or base, middle, and apical segments but also according to coronary artery distribution area, which may detect myocardial microvascular dysfunction at an earlier stage, in DMD patients with LGE-.

Tumoral and peritumoral vascularization of brain tumours: a study comparing an intraoperative ultrasensitive Doppler and a preoperative first-pass perfusion MRI

IntroductionSurgery for gliomas can be guided by neuronavigation using magnetic resonance imaging (MRI) and intraoperative B-mode ultrasound. An ultrasensitive Doppler (USD) using plane waves is a new method of microvascularization imaging which can be used intraoperatively and could identify tumoral and peritumoral areas with neoangiogenesis but its value requires evaluation. The aim of this pilot study then was to evaluate the correlations between ultrasound measurements of glioma vascularization (tumoral and peritumoral region) obtained by a USD intraoperatively and first-pass perfusion measurements obtained on preoperative MRI. Methods18 patients with proven glial tumors were selected for the analysis. They underwent preoperative MRI and intraoperative USD acquisition. The MRI scans were re-aligned to the reference ultrasound slice plane, and for each patient a segmentation of the tumoral and peritumoral zone was performed. Two perfusion parameters were studied: relative cerebral tumor blood volume (rCCBV) in MRI and fractional moving blood volume (FMBV) in a USD. We studied the correlations between mean rCCBV and mean FMBV measured in the tumoral and peritumoral zones in the reference ultrasound slice plane. ResultsThe mean rCCBV and mean FMBV measured in the tumoral zone were significantly and strongly correlated (r = 0.80; p < 0.001). The mean rCCBV and mean FMBV measured in the peritumoral zone were not statistically correlated, although a tendency towards a correlation was noted (r = 0.45; p = 0.067). ConclusionThere was a good correlation between a tumor FMBV obtained by a USD intraoperatively and rCCBV on a preoperative MRI validating the reliability of USD for intraoperative analyses of tumor microvascularization in gliomas.

A simplified method to correct saturation of arterial input function for cardiac magnetic resonance first-pass perfusion imaging: validation with simultaneously acquired PET

BackgroundFirst-pass perfusion imaging in magnetic resonance imaging (MRI) is an established method to measure myocardial blood flow (MBF). An obstacle for accurate quantification of MBF is the saturation of blood pool signal intensity used for arterial input function (AIF). The objective of this project was to validate a new simplified method for AIF estimation obtained from single-bolus and single sequence perfusion measurements. The reference MBF was measured simultaneously on 13N-ammonia positron emission tomography (PET). MethodsSixteen patients with clinically confirmed myocardial ischemia were imaged in a clinical whole-body PET-MRI system. PET perfusion imaging was performed in a 10-min acquisition after the injection of 10 mCi of 13N-ammonia. The MRI perfusion acquisition started simultaneously with the start of the PET acquisition after the injection of a 0.075 mmol/kg gadolinium contrast agent. Cardiac stress imaging was initiated after the administration of regadenoson 20 s prior to PET-MRI scanning. The saturation part of the MRI AIF data was modeled as a gamma variate curve, which was then estimated for a true AIF by minimizing a cost function according to various boundary conditions. A standard AHA 16-segment model was used for comparative analysis of absolute MBF from PET and MRI. ResultsOverall, there were 256 segments in 16 patients, mean resting perfusion for PET was 1.06 ± 0.34 ml/min/g and 1.04 ± 0.30 ml/min/g for MRI (P = 0.05), whereas mean stress perfusion for PET was 2.00 ± 0.74 ml/min/g and 2.12 ± 0.76 ml/min/g for MRI (P < 0.01). Linear regression analysis in MBF revealed strong correlation (r = 0.91, slope = 0.96, P < 0.001) between PET and MRI. Myocardial perfusion reserve, calculated from the ratio of stress MBF over resting MBF, also showed a strong correlation between MRI and PET measurements (r = 0.82, slope = 0.81, P < 0.001). ConclusionThe results demonstrated the feasibility of the simplified AIF estimation method for the accurate quantification of MBF by MRI with single sequence and single contrast injection. The MRI MBF correlated strongly with PET MBF obtained simultaneously. This post-processing technique will allow easy transformation of clinical perfusion imaging data into quantitative information.

Evaluation of coronary microvascular dysfunction and risk factors in children and youth with Turner syndrome by magnetic resonance myocardial perfusion imaging.

Turner syndrome (TS) has an increased predisposition to ischaemic heart disease and the status of coronary microcirculation in TS is largely unknown. This study aims to evaluate myocardial microvascular function in TS using first-pass magnetic resonance perfusion imaging and determine significant risk factors contributing to microvascular dysfunction in the early stage. Perspective cohort study. The study cohort consisted of 67 children and youth with TS and 32 age- and gender-matched controls. Measurements Clinical characteristics, left ventricle (LV) volume and functionand cardiovascular magnetic resonance-derived myocardial perfusion parameters were assessed. Univariable and multivariable linear regression analyses were performed to assess the potential risk factors for microvascular dysfunction. Microvascular perfusion decreased in TS in global and segmented myocardium as reflected in the lower upslopecor and maximum signal intensity (MaxSI) of LV myocardium compared to controls. Multivariable linear regression analysis indicated that age (β = -0.107, 95% confidence interval [CI] = -0.201 to -0.013, p = .026) and being overweight/obese (β = -1.155, CI = -2.134 to -0.176, p = .021) were independent impact factors of microvascular dysfunction. Subgroup analysis showed the upslopecor of older patients with TS decreased more significantly compared with that of normal controls. Upslopecor and MaxSI were lower in overweight/obese patients with TS than in patients with normal body mass index (BMI) and controls. Myocardial microvascular dysfunction can occur in children and youth patients with TS. Age and overweight/obesity were the independent risk factors of microvascular dysfunction, which imply the importance of lowering BMI for the prevention of coronary heart disease in young TS population.

Assessment of myocardial ischemia by strain dobutamine stress echocardiography and cardiac magnetic resonance perfusion imaging before and after coronary artery bypass grafting.

Following coronary artery bypass grafting (CABG), testing for myocardial ischemia by noninvasive imaging is often hampered by false-positive results. The aim of this study was to find test parameters with the best potential to identify myocardial ischemia in post-CABG patients. Fifty-two consecutive patients scheduled for CABG, underwent both dobutamine stress echocardiography (DSE) and cardiac magnetic resonance first-pass perfusion imaging (CMR-FPPI) with adenosine vasodilation, before and 8-10months after the surgical revascularization. A pathologic biphasic stress response (PBR) expresses the presence of contractile reserve during low-dose dobutamine that decreases to hypo- or akinesia provoked by high-dose dobutamine. During DSE, potential PBR, segmental wall-motion score (WMS) as well as peak-systolic longitudinal strain (PLS) at peak-dose dobutamine were assessed. Post-CABG, there was still a relatively high prevalence of ischemia-positive segments evaluated by deformation imaging, but the number of such segments was significantly lower by PBR (20% and 22%) compared with peak-dose strain and WMS (62% and 77%, respectively; P<.05). The use of PBR instead of peak-dose WMS and strain could reduce the number of false-positive test results post-CABG. Among all imaging modalities tested, PBR by WMS and strain may be useful parameters for identifying patients with the need for new revascularization. We furthermore found that DSE may be interpreted as positive when revealing at least three ischemia-positive segments. The sensitivity of these test modalities for detecting coronary restenosis needs to be determined in further studies on a cohort of symptomatic post-CABG patients.

033 - Subepicardial hyperemia on contrast-enhanced first-pass magnetic resonance perfusion imaging is useful for the diagnosis of acute myocarditis

033 - Subepicardial hyperemia on contrast-enhanced first-pass magnetic resonance perfusion imaging is useful for the diagnosis of acute myocarditis

First-pass myocardial perfusion MRI with reduced subendocardial dark-rim artifact using optimized Cartesian sampling.

The presence of subendocardial dark-rim artifact (DRA) remains an ongoing challenge in first-pass perfusion (FPP) cardiac magnetic resonance imaging (MRI). We propose a free-breathing FPP imaging scheme with Cartesian sampling that is optimized to minimize the DRA and readily enables near-instantaneous image reconstruction. The proposed FPP method suppresses Gibbs ringing effects-a major underlying factor for the DRA-by "shaping" the underlying point spread function through a two-step process: 1) an undersampled Cartesian sampling scheme that widens the k-space coverage compared to the conventional scheme; and 2) a modified parallel-imaging scheme that incorporates optimized apodization (k-space data filtering) to suppress Gibbs-ringing effects. Healthy volunteer studies (n = 10) were performed to compare the proposed method against the conventional Cartesian technique-both using a saturation-recovery gradient-echo sequence at 3T. Furthermore, FPP imaging studies using the proposed method were performed in infarcted canines (n = 3), and in two symptomatic patients with suspected coronary microvascular dysfunction for assessment of myocardial hypoperfusion. Width of the DRA and the number of DRA-affected myocardial segments were significantly reduced in the proposed method compared to the conventional approach (width: 1.3 vs. 2.9 mm, P < 0.001; number of segments: 2.6 vs. 8.7; P < 0.0001). The number of slices with severe DRA was markedly lower for the proposed method (by 10-fold). The reader-assigned image quality scores were similar (P = 0.2), although the quantified myocardial signal-to-noise ratio was lower for the proposed method (P < 0.05). Animal studies showed that the proposed method can detect subendocardial perfusion defects and patient results were consistent with the gold-standard invasive test. The proposed free-breathing Cartesian FPP imaging method significantly reduces the prevalence of severe DRAs compared to the conventional approach while maintaining similar resolution and image quality. 2 J. Magn. Reson. Imaging 2017;45:542-555.

Usefulness of Subepicardial Hyperemia on Contrast-Enhanced First-Pass Magnetic Resonance Perfusion Imaging for Diagnosis of Acute Myocarditis

Hyperemia is a major criterion for the diagnosis of acute myocarditis on cardiac magnetic resonance imaging but its assessment is challenging and time consuming. We evaluated the usefulness of the contrast-enhanced first-pass perfusion (FPP) on magnetic resonance imaging for detecting subepicardial hyperemia in acute myocarditis. Forty-seven consecutive patients (mean age: 42 ± 15.6years; 35 men) with a definite diagnosis of acute myocarditis according to the state-of-the-art guidelines were included and compared with 16 control subjects. FPP was evaluated by 2 blinded observers and compared with the reference late gadolinium enhancement. Detection of hyperemia was performed on both qualitative and quantitative methods. Relative increased signal intensity (SI) in the subepicardial hyperemic layer was measured with SI ratio (SI of the subepicardial layer/SI of the immediately adjacent subendocardial layer). Twenty-four patients (51%) with acute myocarditis exhibited subepicardial hyperemia, detected with a good interobserver reproducibility (kappa coefficient: 0.75). The SI in the myocardium of myocarditis patients was increased compared with controls (1.08 ± 0.03 vs 0.945 ± 0.04, p= 0.03) and the SI in myocarditis patients with hyperemia compared with those without hyperemia (1.22 ± 0.04 vs 0.94 ± 0.04, p <0.0001). Sensitivity, specificity, positive predictive, and negative predictive values of FPP for detecting hyperemia were 85%, 94%, 85%, and 93%, respectively. In conclusion, contrast-enhanced first-pass magnetic resonance imaging is a fast and useful method for assessing myocardial hyperemia in patients with acute myocarditis.

A quantitative high resolution voxel-wise assessment of myocardial blood flow from contrast-enhanced first-pass magnetic resonance perfusion imaging: microsphere validation in a magnetic resonance compatible free beating explanted pig heart model.

To assess the feasibility of high-resolution quantitative cardiovascular magnetic resonance (CMR) voxel-wise perfusion imaging using clinical 1.5 and 3 T sequences and to validate it using fluorescently labelled microspheres in combination with a state of the art imaging cryomicrotome in a novel, isolated blood-perfused MR-compatible free beating pig heart model without respiratory motion. MR perfusion imaging was performed in pig hearts at 1.5 (n = 4) and 3 T (n = 4). Images were acquired at physiological flow ('rest'), reduced flow ('ischaemia'), and during adenosine-induced hyperaemia ('stress') in control and coronary occlusion conditions. Fluorescently labelled microspheres and known coronary myocardial blood flow represented the reference standards for quantitative perfusion validation. For the comparison with microspheres, the LV was divided into 48 segments based on a subdivision of the 16 AHA segments into subendocardial, midmyocardial, and subepicardial subsegments. Perfusion quantification of the time-signal intensity curves was performed using a Fermi function deconvolution. High-resolution quantitative voxel-wise perfusion assessment was able to distinguish between occluded and remote myocardium (P < 0.001) and between rest, ischaemia, and stress perfusion conditions at 1.5 T (P < 0.001) and at 3 T (P < 0.001). CMR-MBF estimates correlated well with the microspheres at the AHA segmental level at 1.5 T (r = 0.94, P < 0.001) and at 3 T (r = 0.96, P < 0.001) and at the subendocardial, midmyocardial, and subepicardial level at 1.5 T (r = 0.93, r = 0.9, r = 0.88, P < 0.001, respectively) and at 3 T (r = 0.91, r = 0.95, r = 0.84, P < 0.001, respectively). CMR-derived voxel-wise quantitative blood flow assessment is feasible and very accurate compared with microspheres. This technique is suitable for both clinically used field strengths and may provide the tools to assess extent and severity of myocardial ischaemia.

Residual Ischemia After Revascularization in Multivessel Coronary Artery Disease

Revascularization strategies for multivessel coronary artery disease include percutaneous coronary intervention and coronary artery bypass grafting. In this study, we compared the completeness of revascularization as assessed by coronary angiography and by quantitative serial perfusion imaging using cardiovascular magnetic resonance. Patients with multivessel coronary disease were recruited into a randomized trial of treatment with either coronary artery bypass grafting or percutaneous coronary intervention. Angiographic disease burden was determined by the Bypass Angioplasty Revascularization Investigation (BARI) myocardial jeopardy index. Cardiovascular magnetic resonance first-pass perfusion imaging was performed before and 5 to 6 months after revascularization. Using model-independent deconvolution, hyperemic myocardial blood flow was evaluated, and ischemic burden was quantified. Sixty-seven patients completed follow-up (33 coronary artery bypass grafting and 34 percutaneous coronary intervention). The myocardial jeopardy index was 80.7±15.2% at baseline and 6.9±11.3% after revascularization (P<0.0001), with revascularization deemed complete in 62.7% of patients. Relative to cardiovascular magnetic resonance, angiographic assessment overestimated disease burden at baseline (80.7±15.2% versus 49.9±29.2% [P<0.0001]), but underestimated it postprocedure (6.9±11.3% versus 28.1±33.4% [P<0.0001]). Fewer patients achieved complete revascularization based on functional criteria than on angiographic assessment (38.8% versus 62.7%; P=0.015). After revascularization, hyperemic myocardial blood flow was significantly higher in segments supplied by arterial bypass grafts than those supplied by venous grafts (2.04±0.82 mL/min per gram versus 1.89±0.81 mL/min per gram, respectively; P=0.04). Angiographic assessment may overestimate disease burden before revascularization, and underestimate residual ischemia after revascularization. Functional data demonstrate that a significant burden of ischemia remains even after angiographically defined successful revascularization.

Assessment of coronary microvascular dysfunction in hypertrophic cardiomyopathy: First-pass myocardial perfusion cardiovascular magnetic resonance imaging at 1.5 T

To evaluate the integrity of the coronary microvasculature in patients with hypertrophic cardiomyopathy (HCM) using first-pass magnetic resonance perfusion imaging. Twenty-two patients with HCM and 13 healthy volunteers underwent cardiac magnetic resonance imaging (CMR) at rest. Imaging protocols included short axis cine, first-pass myocardial perfusion, and late-phase contrast-enhanced imaging. Left ventricular end-diastolic wall thickness (EDTH), myocardial thickening, maximal upslope of time-intensity curve (slopemax), and late myocardial gadolinium enhancement (LGE) were assessed for each myocardial segment. The differences in slopemax, myocardial thickening, and EDTH between healthy volunteers and HCM patients were evaluated as were differences among hypertrophic segments of different severities (mild, moderate, and severe hypertrophy) in a one-way analysis of variance analysis. The differences in slopemax, myocardial thickening, and EDTH between the segments with and without LGE were compared by independent-sample t-test. A Pearson correlation test was used to determine the relationships between slopemax, EDTH, and myocardial thickening. Slopemax was statistically significantly less in HCM patients; the degree of myocardial thickening was also significantly reduced (p < 0.001). Slopemax and the degree of thickening statistically significantly decreased with increasing degrees of myocardial hypertrophy (p < 0.05). Differences in slopemax, myocardial thickening, and EDTH were observed between segments with and without LGE (p < 0.05). Slopemax and myocardial thickening were negatively correlated with EDTH. First-pass myocardial perfusion CMR with slopemax measurements demonstrates microvascular coronary dysfunction in patients with HCM, a determination that may aid in risk stratification, therapeutic planning, and determination of prognosis for HCM.

A quantitative high resolution assessment of myocardial blood flow from contrast-enhanced first-pass magnetic resonance perfusion imaging: microsphere validation in a magnetic resonance compatible free beating explanted pig heart model

A quantitative high resolution assessment of myocardial blood flow from contrast-enhanced first-pass magnetic resonance perfusion imaging: microsphere validation in a magnetic resonance compatible free beating explanted pig heart model

Arterial Spin Labeling MR Imaging Reproducibly Measures Peak-Exercise Calf Muscle Perfusion: A Study in Patients With Peripheral Arterial Disease and Healthy Volunteers

This study hypothesized that arterial spin labeling (ASL) magnetic resonance (MR) imaging at 3-T would be a reliable noncontrast technique for measuring peak exercise calf muscle blood flow in both healthy volunteers and patients with peripheral arterial disease (PAD) and will discriminate between these groups. Prior work demonstrated the utility of first-pass gadolinium-enhanced calf muscle perfusion MR imaging in patients with PAD. However, patients with PAD often have advanced renal disease and cannot receive gadolinium. PAD patients had claudication and an ankle brachial index of 0.4 to 0.9. Age-matched normal subjects (NL) had no PAD risk factors and were symptom-free with exercise. All performed supine plantar flexion exercise in a 3-T MR imaging scanner using a pedal ergometer until exhaustion or limiting symptoms and were imaged at peak exercise with 15 averaged ASL images. Peak perfusion was measured from ASL blood flow images by placing a region of interest in the calf muscle region with the greatest signal intensity. Perfusion was compared between PAD patients and NL and repeat testing was performed in 12 subjects (5 NL, 7 PAD) for assessment of reproducibility. Peak exercise calf perfusion of 15 NL (age: 54 ± 9 years) was higher than in 15 PAD patients (age: 64 ± 5 years, ankle brachial index: 0.70 ± 0.14) (80 ± 23 ml/min – 100 g vs. 49 ± 16 ml/min/100 g, p < 0.001). Five NL performed exercise matched to PAD patients and again demonstrated higher perfusion (84 ± 25 ml/min – 100 g, p < 0.002). As a measure of reproducibility, intraclass correlation coefficient between repeated studies was 0.87 (95% confidence interval [CI]: 0.61 to 0.96). Interobserver reproducibility was 0.96 (95% CI: 0.84 to 0.99). ASL is a reproducible noncontrast technique for quantifying peak exercise blood flow in calf muscle. Independent of exercise time, ASL discriminates between NL and PAD patients. This technique may prove useful for clinical trials of therapies for improving muscle perfusion, especially in patients unable to receive gadolinium.

Dynamic susceptibility contrast-enhanced first-pass perfusion MR imaging in patients with subclinical hepatic encephalopathy

Subclinical hepatic encephalopathy (SHE) is frequently reported on single-photon emission computed tomography (SPECT), but is rarely described with magnetic resonance (MR) techniques. This study aimed to investigate hemodynamic changes in brain basal ganglia in patients with SHE using dynamic susceptibility contrast (DSC)-enhanced MR perfusion imaging. Twelve patients with SHE and ten age- and education-matched volunteers agreed to undergo MR examination. The scanning protocol included conventional anatomical images and DSC-enhanced perfusion MR imaging. Using MGH perfusion software, parameter maps of cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) were created. The bilateral caudate nucleus head, globus pallidus, putamen and thalamus were selected as regions of interest (ROI), with ipsilateral white matter of the frontal lobe used as reference. Ratios (ROI versus ipsilateral white matter in frontal lobe) for CBF, CBV and MTT in the patient group were compared with those in the control group. The CBF ratios for every ROI were higher in SHE patients versus the controls. Statistically, significant increases were detected in the left globus pallidus, putamen and thalamus (P<0.05). For MTT, the reduction in values reached statistical significance in the right head of the caudate nucleus and bilateral thalamus (P<0.05). CBV values were not significantly different compared with those of the control group (P>0.05). Increased CBF and decreased MTT values in the basal ganglia and thalamus were identified in patients with SHE. The CBF increase was compatible with the idea that the CBF is redistributed from cortical areas to the basal ganglia structures.

Myocardial Perfusion Magnetic Resonance Imaging Using Sliding-Window Conjugate-Gradient HYPR Methods in Canine With Stenotic Coronary Arteries

First-pass perfusion magnetic resonance imaging (MRI) is a promising technique for detecting ischemic heart disease. However, the diagnostic value of the method is limited by the low spatial coverage, resolution, signal-to-noise ratio (SNR), and cardiac motion-related image artifacts. A combination of sliding window and conjugate-gradient HighlY constrained back-PRojection reconstruction (SW-CG-HYPR) method has been proposed in healthy volunteer studies to reduce the acquisition window for each slice while maintaining the temporal resolution of 1 frame per heartbeat in myocardial perfusion MRI. This method allows for improved spatial coverage, resolution, and SNR. In this study, we use a controlled animal model to test whether the myocardial territory supplied by a stenotic coronary artery can be detected accurately by SW-CG-HYPR perfusion method under pharmacological stress. Results from 6 mongrel dogs (15-25 kg) studies demonstrate the feasibility of SW-CG-HYPR to detect regional perfusion defects. Using this method, the acquisition time per cardiac cycle was reduced by a factor of 4, and the spatial coverage was increased from 2 to 3 slices to 6 slices as compared with the conventional techniques including both turbo-Fast Low Angle Short (FLASH) and echoplanar imaging (EPI). The SNR of the healthy myocardium at peak enhancement with SW-CG-HYPR (12.68 ± 2.46) is significantly higher (P < 0.01) than the turbo-FLASH (8.65 ± 1.93) and EPI (5.48 ± 1.24). The spatial resolution of SW-CG-HYPR images is 1.2 × 1.2 × 8.0 mm, which is better than the turbo-FLASH (1.8 × 1.8 × 8.0 mm) and EPI (2.0 × 1.8 × 8.0 mm). Sliding-window CG-HYPR is a promising technique for myocardial perfusion MRI. This technique provides higher image quality with respect to significantly improved SNR and spatial resolution of the myocardial perfusion images, which might improve myocardial perfusion imaging in a clinical setting.

Accuracy of Cardiac Magnetic Resonance of Absolute Myocardial Blood Flow With a High-Field System: Comparison With Conventional Field Strength

The aim of this study was to determine the accuracy of cardiac magnetic resonance (CMR) first pass (FP) perfusion measures of absolute myocardial blood flow (MBF) with a 3.0-T magnet and compare these measures with FP perfusion at 1.5-T with absolute MBF by labeled microspheres as the gold standard. First-pass magnetic resonance (MR) myocardial perfusion imaging can quantify MBF, but images are of low signal at conventional magnetic field strength due to the need for rapid acquisition. A pig model was used to alter MBF in a coronary artery during FP CMR (intracoronary adenosine followed by ischemia). This produces an active zone with a range of MBF and a control zone. Microspheres were injected into the left atrium with concurrent reference sampling. FP MR perfusion imaging was performed at 1.5-T (n = 9) or 3.0-T (n = 8) with a saturation-recovery gradient echo sequence in short-axis slices during a bolus injection of 0.025 mmol/kg gadolinium-diethylenetriamine pentaacetic acid. Fermi function deconvolution was performed on active and control region of interest from short-axis slices with an arterial input function derived from the left ventricular cavity. These MR values of MBF were matched to microsphere values obtained from short-axis slices at pathology. Occlusion MBF was 0.21 +/- 0.26 ml/min/g, adenosine MBF was 2.28 +/- 0.99 ml/min/g, and control zone MBF was 0.70 +/- 0.22 ml/min/g. The correlation of MR FP CMR with microsphere was close for both field strengths: 3.0-T, r = 0.98, p < 0.0001 and 1.5-T, r = 0.95, p < 0.0001. The 95% confidence limits of agreement were slightly narrower at 3.0-T (3.0-T = 0.49 ml/min/g, 1.5-T = 0.68 ml/min/g, p < 0.05). The FP CMR image characteristics were better at 3.0-T (noise and contrast enhancement were both superior at 3.0-T). In myocardial zones where MBF <0.50 ml/min/g, the correlation with microspheres was closer at 3.0-T (r = 0.55 at 1.5-T, r = 0.85 at 3.0-T). Absolute MBF by FP perfusion imaging is accurate at both 1.5- and 3.0-T. Signal quality is better at 3.0-T, which might confer a benefit for estimating MBF in ischemic zones.

Regional myocardial perfusion abnormalities: Fractional flow reserve versus cardiac magnetic resonance first-pass perfusion imaging

Identification of the functional severity of intermediate coronary artery lesions is challenging for the interventional cardiologist. Functional severity can be measured invasively using the fractional flow reserve (FFR). However, FFR has the disadvantage of being invasive and associated with radiation exposure. Cardiac MRI (CMR) offers the opportunity to assess myocardial perfusion noninvasively. A semiquantitative index of myocardial perfusion (perfusion reserve index or PRI) can be obtained from the first-pass of a bolus of gadolinium through the myocardium. Studies comparing the invasive FFR to CMR perfusion imaging in patients with coronary artery stenosis of undefined significance have demonstrated that CMR first-pass perfusion imaging may be useful for the assessment of their functional significance. However, in patients with a high prevalence of microvascular dysfunction, the value of this method may be limited because the PRI may be influenced by both the epicardial conductance vessel function as well as microvascular function.

Myocardial Microinfarction after Coronary Microembolization in Swine: MR Imaging Characterization

To use first-pass perfusion and delayed-enhanced (DE) magnetic resonance (MR) imaging for the detection of the early effects of coronary microembolization on myocardial perfusion and viability. Approval was obtained from the institutional committee on animal research. A hybrid x-ray and MR imaging system was used to guide the endovascular catheter and quantify the left anterior descending coronary artery (LAD) perfusion territory before microembolization and ischemic myocardium and microinfarction after microembolization. The embolic agent was selectively delivered in the LAD in six pigs. First-pass perfusion MR imaging was performed 1 hour and 1 week after microembolization. Microinfarction was measured on DE MR images in beating and nonbeating hearts (high-spatial-resolution sequence) by using extracellular and blood pool MR contrast media and after death. The Wilcoxon signed rank test and correlation analysis were used. The LAD perfusion territory was 35% of left ventricular (LV) mass +/- 2 (standard error of the mean). Microembolization caused perfusion deficit in 15.7% of LV mass +/- 2.6 compared with that of LAD territory (P = .03). At 1 week, perfusion parameters improved and the extent of hypoperfused territory declined (4.6% of LV mass +/- 1.4, P = .03). Microinfarction size expanded from 1.4% of LV mass +/- 0.2 at 1 hour to 7.5% of LV mass +/- 1.2 at 1 week. In nonbeating hearts and at triphenyltetrazolium chloride staining at 1 week, microinfarction size was 7.6% of LV mass +/- 1.4 and 7.2% of LV mass +/- 1.5, respectively. There was no correlation between the ejection fraction and the extents of microinfarction or hypoperfused territory. Histopathologic findings confirmed the presence of patchy microinfarction. Coronary microembolization caused persistent decline in myocardial perfusion at first-pass perfusion imaging. DE MR imaging has the potential to help reliably quantify subacute microinfarction. The magnitude of LV dysfunction is not related to the extents of microinfarction or hypoperfused territory.

Intracoronary Injection of Contrast Media Maps the Territory of the Coronary Artery: An MRI Technique for Assessing the Effects of Locally Delivered Angiogenic Therapies

The effects of locally delivered angiogenic factors or stem cells on the coronary artery perfusion territory are not well defined. Therefore, the aim of this study was to determine the ability of the selective injection of magnetic resonance contrast media (MR-CM) to map and quantify the territories of the major coronary arteries. Selective coronary catheterization (n = 16 pigs) was performed under x-ray and magnetic resonance imaging (MRI) fluoroscopy in an x-ray and magnetic resonance suite. Catheters were placed in the left anterior descending (LAD), circumflex, or right coronary artery. The coronary perfusion territories were mapped by the intracoronary injection of MR-CM using first-pass perfusion (FPP) and early contrast-enhanced (CE) MRI. Cine MRI was used to quantify left ventricular (LV) mass. In 12 animals, the LAD coronary artery was occluded by microspheres to create infarctions. Infarct size was measured on delayed enhanced (DE) MRI after the intravenous injection of MR-CM. X-ray and magnetic resonance fluoroscopy were successfully used to catheterize the coronary arteries. The perfusion territories of the coronary arteries were defined as hyperenhanced regions on FPP and CE MRI. The LAD coronary artery territory was 33.7 +/- 2.2% of LV mass on FPP MRI and 33.0 +/- 2.3% on CE MRI (P = .63). Bland-Altman analysis showed close agreement between the two methods (0.7 +/- 5.0%). DE MRI demonstrated the infarcted myocardium as hyperenhanced subregions of the perfusion territory (7.5 +/- 1.2% of LV mass). Interventional cardiac x-ray and magnetic resonance fluoroscopy can be used to map and quantify the perfusion territory of each coronary artery. This experimental method can be used before and after the local delivery of angiogenic factors and stem cell therapy to determine their efficacy.

Comparison of quantitative coronary angiography and first‐pass perfusion magnetic resonance imaging for the detection of an impaired coronary perfusion in nonsevere coronary stenosis

To compare quantitative coronary angiography (QCA) and first-pass perfusion magnetic resonance imaging (FPP-MRI) in symptomatic patients with nonsevere coronary stenosis to detect a reduced coronary flow velocity reserve (CFVR). In 35 patients, FPP-MRI and CFVR measurements were performed in 40 coronary arteries with a diameter stenosis (DS) <70% by QCA. From FPP-MRI a myocardial perfusion reserve index (MPRI) was calculated. CFVR was calculated as the ratio of the average peak flow velocity during infusion of adenosine and at rest and was considered reduced if <2. Diagnostic performance of MPRI and DS to detect a reduced CFVR was compared by receiver operating characteristic (ROC) curve analysis. CFVR was reduced in 16 coronary arteries (40%). Mean DS did not differ in coronary arteries with a reduced CFVR (41.0% +/- 13.3) and a normal CFVR (36.5% +/- 12.3; P = 0.281). Mean MPRI was lower in coronary arteries with a reduced CFVR (1.12 +/- 0.12) compared to a normal CFVR (1.33 +/- 0.2; P < 0.001). Sensitivity, specificity, and area under the ROC curve (AUC) were higher for MPRI (81%, 79%, 0.84) than for DS (56%, 58%, 0.60). FPP-MRI detects impaired CFVR in symptomatic patients with nonsevere coronary stenosis more accurately than QCA and can identify patients with symptomatic ischemia.