Coronary artery size and origin imaging in children: a comparative study of MRI and trans-thoracic echocardiography.

BACKGROUND: The purpose of this study was to see how coronary magnetic resonance angiography (CMRA) compared to echocardiography for the detection of coronary artery origins and to compare CMRA measurements for coronary dimensions in children with published echocardiographic reference values. METHODS: Enrolled patients underwent dual cardiac phase CMRA and echocardiography under the same anesthetic. Echocardiographic measurements of the right coronary artery (RCA), left anterior descending (LAD) and left main (LM) were made. CMRA dimensions were assessed manually at the same points as the echocardiographic measurements. The number of proximal LAD branches imaged was also recorded in order to give an estimate of distal coronary tree visualization. RESULTS: Fifty patients (24 boys, mean age 4.0 years (range 18 days to 18 years)) underwent dual-phase CMRA. Coronary origins were identified in 47/50 cases for CMRA (remaining 3 were infants aged 3, 9 and 11 months). In comparison, origins were identified in 41/50 cases for echo (remaining were all older children). CMRA performed better than echocardiography in terms of distal visualization of the coronary tree (median 1 LAD branch vs. median 0; p = 0.001). Bland-Altman plots show poor agreement between echocardiography and CMRA for coronary measurements. CMRA measurements did vary according to cardiac phase (systolic mean 1.90, s.d. 0.05 mm vs. diastolic mean 1.84, s.d. 0.05 mm; p = 0.002). CONCLUSIONS: Dual-phase CMRA has an excellent (94 %) success rate for the detection of coronary origins in children. Newborn infants remain challenging and echocardiography remains the accepted imaging modality for this age group. Echocardiographic reference ranges are not applicable to CMRA measurements as agreement was poor between modalities. Future coronary reference values, using any imaging modality, should quote the phase in which it was measured.

Cardiac magnetic resonance and electroanatomical mapping of acute and chronic atrial ablation injury: a histological validation study.

AIMS: To provide a comprehensive histopathological validation of cardiac magnetic resonance (CMR) and endocardial voltage mapping of acute and chronic atrial ablation injury. METHODS AND RESULTS: 16 pigs underwent pre-ablation T2-weighted (T2W) and late gadolinium enhancement (LGE) CMR and high-density voltage mapping of the right atrium (RA) and both were repeated after intercaval linear radiofrequency ablation. Eight pigs were sacrificed following the procedure for pathological examination. A further eight pigs were recovered for 8 weeks, before chronic CMR, repeat RA voltage mapping and pathological examination. Signal intensity (SI) thresholds from 0 to 15 SD above a reference SI were used to segment the RA in CMR images and segmentations compared with real lesion volumes. The SI thresholds that best approximated histological volumes were 2.3 SD for LGE post-ablation, 14.5 SD for T2W post-ablation and 3.3 SD for LGE chronically. T2-weighted chronically always underestimated lesion volume. Acute histology showed transmural injury with coagulative necrosis. Chronic histology showed transmural fibrous scar. The mean voltage at the centre of the ablation line was 3.3 mV pre-ablation, 0.6 mV immediately post-ablation, and 0.3 mV chronically. CONCLUSION: This study presents the first histopathological validation of CMR and endocardial voltage mapping to define acute and chronic atrial ablation injury, including SI thresholds that best match histological lesion volumes. An understanding of these thresholds may allow a more informed assessment of the underlying atrial substrate immediately after ablation and before repeat catheter ablation for atrial arrhythmias.

Detection and grading of coronary allograft vasculopathy in children with contrast-enhanced magnetic resonance imaging of the coronary vessel wall.

BACKGROUND: Coronary allograft vasculopathy is the leading cause of late death after heart transplantation in children. It is poorly detected by conventional angiography. Intravascular ultrasound is invasive and costly. This study shows that magnetic resonance imaging (MRI) late gadolinium enhancement (LGE) of the coronary vessel wall can detect and grade coronary allograft vasculopathy. METHODS AND RESULTS: Twenty-four children (10 male; age range, 9-17 years) underwent coronary angiography, intravascular ultrasound, and MRI. Maximal intimal thickness and mean intimal index were recorded. MRI included coronary magnetic resonance angiogram and LGE vessel wall imaging with 1.5 T (n=12) and 3.0 T (n=12). Ten healthy control subjects also underwent LGE MRI. Mean time posttransplantation was 5.5 years (range, 0.25-14 years). Seven patients had Stanford grade IV coronary allograft vasculopathy on intravascular ultrasound, 3 of whom had angiographic disease. Maximal intimal thickness and mean intimal index were 0.73±0.50 mm and 20.9±10.6%, respectively. On MRI, mean diameter of enhancement of vessel wall was 6.57±4.91 mm, and mean enhancement index (indexed to vessel lumen size) was 1.10±1.72. The control group showed little or no LGE. Correlation of LGE with maximal intimal thickness using the Pearson coefficient was 0.80 (P<0.001) and with mean intimal index was 0.92 (P<0.001). An MRI diameter >7.5 mm gave 86% sensitivity and 93% specificity. CONCLUSIONS: LGE scores correlate well with traditional intravascular ultrasound measures. These promising early results encourage larger-scale clinical studies to investigate whether LGE MRI will allow closer follow-up and better prevention of coronary allograft vasculopathy in children.

Dual inversion-recovery mr imaging sequence for reduced blood signal on late gadolinium-enhanced images of myocardial scar.

PURPOSE: To investigate whether a dual inversion-recovery (IR) prepulse improves scar-to-blood contrast and expert confidence and consistency at late gadolinium-enhanced magnetic resonance (MR) imaging of myocardial scar compared with the standard IR technique at 3.0 T. MATERIALS AND METHODS: The study was approved by the local ethics committee, and all patients provided written informed consent. Twelve men (mean age±standard deviation, 63 years±8) with known myocardial scar underwent MR imaging 10, 20, and 30 minutes after administration of 0.2 mmol/kg gadobutrol with a standard and dual IR sequence. Contrast-to-noise ratios (CNRs) were measured by using region-of-interest analysis, and data were compared with the analysis of variance test. Two experts measured scar size and transmurality, and data were compared with the Student t test and Bland-Altman test. Experts assigned confidence scores for scar detection and transmurality, which were compared with a Wilcoxon matched-pairs signed rank test. RESULTS: Patient data showed improved scar-to-blood CNR for the dual IR technique compared with the standard IR technique at all time points (P<.05). For images obtained 20 minutes after contrast material administration, the dual IR sequence provided higher confidence scores for scar detection and transmurality assessment (P<.05) and resulted in more consistent assessment of scar size and transmurality between readers compared with the IR sequence (P<.05). CONCLUSION: In this preliminary patient study, the dual IR prepulse improved contrast, scar visualization, and expert confidence and reduced expert differences in transmurality and scar size assessment compared with the standard IR technique.

Cross-sectional and in-plane coronary vessel wall imaging using a local inversion prepulse and spiral read-out: a comparison between 1.5 and 3 Tesla.

PURPOSE: To compare cross-sectional and in-plane coronary vessel wall imaging using a spiral readout at 1.5 and 3 Tesla (T). MATERIALS AND METHODS: Free-breathing coronary vessel wall imaging using a local inversion technique and spiral readout was implemented. Images were acquired in ten healthy adult subjects on a 3T clinical scanner using a 32-element cardiac coil and repeated on a 1.5T clinical scanner using a 5-element coil. RESULTS: Cross-sectional and in-plane spiral vessel wall imaging was performed at both 1.5 and 3T. In cross-sectional images, artifact scores were superior at 1.5T (P < 0.05) but no significant difference was found in image quality scores compared with 3T. Image quality (P < 0.01) and artifact scores (P < 0.01) were found to be superior for in-plane images at 1.5T. Vessel wall sharpness in the in-plane orientation was also found to be higher at 1.5T (P < 0.03). CONCLUSION: Although excellent in-plane coronary vessel wall images can be acquired at 3T, the overall robustness may be affected by off-resonance blurring due to increased B0 inhomogeneity compared with 1.5T.

Accelerated aortic imaging using small field of view imaging and electrocardiogram-triggered quadruple inversion recovery magnetization preparation.

PURPOSE: To accelerate and optimize black blood properties of the quadruple inversion recovery (QIR) technique for imaging the abdominal aortic wall. MATERIALS AND METHODS: QIR inversion delays were optimized for different heart rates in simulations and phantom studies by minimizing the steady state magnetization of blood for T(1) = 100-1400 ms. To accelerate and improve black blood properties of aortic vessel wall imaging, the QIR prepulse was combined with zoom imaging and (a) "traditional" and (b) "trailing" electrocardiogram (ECG) triggering. Ten volunteers were imaged pre- and post-contrast administration using a conventional ECG-triggered double inversion recovery (DIR) and the two QIR implementations in combination with a zoom-TSE readout. RESULTS: The QIR implemented with "trailing" ECG-triggering resulted in consistently good blood suppression as the second inversion delay was timed during maximum systolic flow in the aorta. The blood signal-to-noise ratio and vessel wall to blood contrast-to-noise ratio, vessel wall sharpness, and image quality scores showed a statistically significant improvement compared with the traditional QIR implementation with and without ECG-triggering. CONCLUSION: We demonstrate that aortic vessel wall imaging can be accelerated with zoom imaging and that "trailing" ECG-triggering improves black blood properties of the aorta which is subject to motion and variable blood flow during the cardiac cycle.

A technique for the simulation of planar radionuclide images of the kidney.

BACKGROUND: Although Tc-dimercaptosuccinic acid (DMSA) scans are routinely used to quantify relative renal function, no quantification method is universally adopted. Audits using real patient data indicate reasonable consistency but, as the true relative function is unknown, accuracy cannot be assessed. The aim was to simulate realistic DMSA images that can be used to assess accuracy. METHODS: Anatomical models were created from computed tomography (CT) scans of a patient who had also undergone DMSA imaging. Organs that take up DMSA were outlined on CT and each assigned an activity concentration (with renal cortex and medulla modelled separately). The simulated images were visually compared to the patient's clinical images and subtracted to identify differences. Iteration was used on the posterior image to find the organ activities that produced the most realistic simulated image. The optimal activity distribution was then used to also simulate an anterior image. To assess the simulations, the percentage difference was calculated between the counts in each kidney on the real and simulated images. RESULTS: Visually, the clinical and simulated images appear similar and the subtracted images indicate only small differences. The percentage difference in kidney counts between the images was less than 1% for both kidneys on the posterior image and less than 5% on the anterior image. The cortex and medulla activity concentrations were approximately equal. CONCLUSION: A technique for realistic simulation of DMSA images has been devised and should prove useful for evaluating image analysis software.