Gavin Bainbridge

Steady-state free precession magnetic resonance imaging of the heart: comparison with segmented k-space gradient-echo imaging.

Steady‐state free precession imaging is a promising technique for cardiac magnetic resonance imaging (MRI), as it provides improved blood/myocardial contrast in shorter acquisition times compared with conventional gradient‐echo acquisition. The better contrast could improve observer agreement and automatic detection of cardiac contours for volumetric assessment of the ventricles, but measurements might differ from those obtained using conventional methods. We compared volumetric measurements, observer variabilities, and automatic contour detection between a steady‐state free precession imaging sequence (BFFE = balanced fast field echo) and segmented k‐space gradient‐echo acquisition (TFE = turbo field echo) in 41 subjects. With BFFE, significantly higher end‐diastolic and end‐systolic volumes and lower wall thickness, ventricular mass, ejection fraction, and wall motion were observed (P < 0.0001), while interobserver variabilities were lower and automatic contour detection of endocardial contours was more successful. We conclude that the improved image quality of BFFE reduces the observer‐dependence of volumetric measurements of the left ventricle (LV) but results in significantly different values in comparison to TFE measurements. J. Magn. Reson. Imaging 2001;14:230–236.

Myocardial T1 Mapping for Detection of Left Ventricular Myocardial Fibrosis in Chronic Aortic Regurgitation: Pilot Study

OBJECTIVE The aim of this study was to identify diffuse myocardial fibrosis secondary to chronic aortic regurgitation by comparing the T1 relaxation times of left ventricular myocardium in a pilot patient group with a previously established normal range of times. SUBJECTS AND METHODS Eight patients with chronic aortic regurgitation and normal coronary arteries awaiting surgical valve replacement underwent a comprehensive MRI examination that included assessment of left ventricular function, severity of valvular regurgitation, and presence of overt myocardial scar evidenced by delayed enhancement. For each patient, myocardial T1 relaxation times determined with a modified Look-Locker technique before and after contrast administration were compared with values previously established for 15 healthy volunteers. RESULTS There was no statistical difference (p > 0.05) in slice-averaged myocardial T1 relaxation times either before or after gadolinium administration in the patient group compared with the normal range of times. Segmental averaged T1 relaxation times in segments with abnormal wall motion did, however, show statistically significant differences from healthy controls 10, 15, and 20 minutes after administration of gadolinium (510 vs 476 milliseconds, p = 0.001; 532 vs 501 milliseconds, p = 0.002; 560 vs 516 milliseconds, p = 0.001, respectively). Two of the aortic regurgitation patients also had focal areas of myocardial delayed enhancement. CONCLUSION Segment-based myocardial T1 mapping has the potential for showing differences between relaxation times in aortic regurgitation and in normal hearts, suggesting the existence of a diffuse myocardial fibrotic process.

Comparison of right ventricular volume measurement between segmented k‐space gradient‐echo and steady‐state free precession magnetic resonance imaging

To compare right ventricular volume measurements and their reproducibility between steady‐state free precession (SSFP) and conventional turbo gradient‐echo (TGE) imaging.

Left Ventricle Mass Index and the Common, Functional, X-Linked Angiotensin II Type-2 Receptor Gene Polymorphism (−1332 G/A) in Patients With Systemic Hypertension

A common intronic polymorphism, (−1332 G/A) of the angiotensin type-2 receptor gene, located on the X-chromosome, has been reported to be functional. The aim of our study was to evaluate this polymorphism for an association with left ventricular hypertrophy. Left ventricle (LV) mass was measured in 197 patients with systemic hypertension and 60 normal volunteers using a 1.5-Tesla Philips MRI system. Genotyping was performed using a restriction enzyme digestion of an initial 310-bp polymerase chain reaction product that included the angiotensin type-2 (−1332 G/A) locus. The mean LV mass index for the male patients was 94.3±19.6 g/m2 (n= 125) and for the female patients was 71.2±12.0 g/m2 (n=72). Seventy-three (37.1%) of all patients had an elevated LV mass index, defined as the mean LV mass index for normal volunteers plus 2 SD (males 77.8±9.1 g/m2, n= 30; females 61.5±7.5g/m2, n= 30). Comparison of LV mass index of the A_/AA genotype (mean LV mass index= 82.4±21.1 g/m2; n= 123) against that of the G_/GG genotype (mean LV mass index= 88.1±19.0 g/m2; n= 89) as a continuous variable was significant by ANOVA (P = 0.044). χ2 Comparison between subjects with and subjects without left ventricular hypertrophy revealed an excess of the G_/GG genotype among the group with LV hypertrophy (P = 0.031). We observed an association between the angiotensin type-2 receptor (−1332 G) allele and the presence of left ventricular hypertrophy in hypertensive subjects.

Patient adaptive maximal resolution magnetic resonance myocardial stress perfusion imaging

To demonstrate the feasibility of an automatic adaptive acquisition sequence. Magnetic resonance perfusion pulse sequences often leave potential acquisition time unused in patients with lower heart‐rates (HR) and smaller body size.

Heart rate adaptive maximal resolution cardiovascular magnetic resonance myocardial stress perfusion imaging at 3.0T.

Background Myocardial perfusion cardiovascular magnetic resonance (CMR) with vasodilator stress has high diagnostic accuracy for detecting coronary artery disease (CAD). Current CMR perfusion pulse sequences use largely fixed acquisition parameters designed to acquire at least three slices every heart beat, optimized for the heart rates that typically occur during pharmacological stress. In patients with lower heart rates there can be a significant amount of unused potential imaging time [Figure 1]. In those with higher heart rates, acquisition with fixed parameters may not be possible at every heart beat. A more flexible acquisition scheme could optimize acquisition parameters specifically for each patient and heart rate with potential improvements in image quality or temporal resolution. We aimed to assess the feasibility of a perfusion pulse sequence which adapts to the heart rate, maximizing imaging time and acquired spatial resolution.

Overestimation of infarct size following acute myocardial infarction is related to extent of myocardial edema

Background Late gadolinium enhancement (LGE) is an accurate and reproducible method to delineate nonviable myocardium following myocardial infarction (MI). However, in the early stages following acute MI, LGE has been shown to overestimate the size of the infarct zone by up to 30%. The causes for this are unclear, and may be related to tissue remodelling, intracellular contrast uptake, or expansion of the interstitial space. Myocardial edema is a feature of reperfused acute MI, and edematous myocardium has been associated with early contrast enhancement [1]. We hypothesised that the presence of tissue edema is also related to late enhancement, and contributes to overestimation of infarct size in acute MI. Methods 46 patients received CMR examination at 3.0T at 2 days following reperfused ST-elevation acute MI, with follow-up imaging at 10 days and 3 months. Short-axis T2-weighted imaging and cine imaging were performed, as well as LGE imaging 16-20 minutes following administration of 0.1 mmol/kg gadolinium DTPA. Edema volume was measured on T2-weighted imaging and scar volume measured on LGE imaging, both quantified using a semi-automated histogram-based thresholding method (Otsu method). The change in scar volume was compared to the change in edema volume between day 2 and day 10, and between day 2 and 3 months.

Early vs. persistent microvascular obstruction following primary PCI- two pathologies or one? A cardiovascular magnetic resonance study

Background 20-40% of reperfused ST-elevation acute myocardial infarction (STEMI) features microvascular obstruction (MO), which confers adverse prognosis. Different CMR sequences are commonly used to detect MO: first pass perfusion (FPP), early gadolinium enhancement (EGE), and late gadolinium enhancement (LGE). FPP and EGE are more sensitive than LGE for the detection of MO. However, only MO by LGE has been shown to confer prognostic information. It is unclear whether these three

133 Early vs. Late Microvascular Obstruction Following Primary PCI- Two Pathologies or One?

Background Microvascular obstruction (MO) is a feature of 20–40% of reperfused acute ST-elevation myocardial infarction (STEMI), and confers adverse prognosis. Cardiovascular magnetic resonance (CMR) can visualise MO with high resolution and accuracy. MO may be detected by different CMR sequences: first pass perfusion (FPP), early gadolinium enhancement (EGE), and late gadolinium enhancement (LGE). FPP and EGE are more sensitive than LGE for the detection of MO. However, only MO by LGE has been shown to confer prognostic information. It is unclear whether these three methods detect separate pathologies, or whether differences in MO appearances merely reflect contrast distribution over time. We aimed to determine how appearances between these methods are related. Methods 60 patients underwent CMR at 3.0T within 3 days following reperfused first STEMI. MO imaging was performed at identically-planned basal, mid-ventricular and apical short-axis slices. FPP imaging was performed during administration of 0.1 mmol/kg Gd-DTPA contrast. 4 min after contrast administration, EGE imaging was performed, followed by LGE imaging at both 10 min and at 20 min. MO was identified as a dark core within infarcted myocardium. We compared area and transmural extent of MO for each method on a per-patient and a per-slice basis. Results 29 patients (48%) had MO. All patients with MO on LGE also had MO on FPP or EGE, whereas LGE at 10 min failed to detect MO in 9 patients (31%) with MO on FPP, and 8 patients (28%) on EGE. Of 13 patients with MO volume <5 ml on FPP, 12 (92%) had no MO visible on LGE at 20 min. Average visible area of MO per slice decreased with time of measurement (p < 0.001 for trend, Figure 1). MO area by FPP and EGE correlated with LGE at 20 min (r = 0.80; p < 0.001 and r = 0.80; p < 0.001) but MO volume (per patient) by FPP and EGE was on average 236 and 200% larger than LGE. Decrease in MO volume over time correlated strongly with size of MO (r = 0.95, p < 0.01, Figure 2) and transmural extent of MO (r = 0.77, p < 0.01). Abstract 133 Figure 1 Decrease in apparent area of MO visible after administration of contrast Abstract 133 Figure 2 Change in MO volume over time is closely correlated with volume of MO Conclusions The reduction in visible size of MO is proportional to extent of MO and time from contrast administration. The strong correlation with MO size and time suggests that the reduction in MO size between methods is explained by contrast diffusion into the MO zone, rather than differing clinical or imaging factors. Smaller areas of MO on EGE and FPP become undetectable on LGE, while larger areas are detectable but smaller on LGE. MO by LGE therefore identifies more extensive MO than FPP or EGE, possibly explaining its higher predictive value for adverse prognosis following STEMI.