Jürgen Gieseke

Noninvasive Quantification of Left-to-Right Shunt in Pediatric Patients Phase-Contrast Cine Magnetic Resonance Imaging Compared With Invasive Oximetry

Background—Blood flow can be quantified noninvasively by phase-contrast cine MRI (PC-MRI) in adults. Little is known about the feasibility of the method in children with congenital heart disease. Methods and Results—In 50 children (mean age 6.2 years, range 1.1 to 17.7 years) with an atrial- or ventricular-level shunt, blood flow rate in the great vessels was determined by PC-MRI, and the ratio of pulmonary to aortic flow (˙Qp/˙Qs) was compared with ˙Qp/˙Qs by oximetry. We found a difference of 2% and a range of −20% to +26% (limits of agreement, mean±2 SD). In another 7 children with congenital heart disease but no cardiac shunting (mean age 7.9 years, range 1.3 to 13.5 years), ˙Qp/˙Qs by PC-MRI was 1.02 (SD ±0.06). No difference between systemic venous and aortic flow volumes was found (range −17% to +20%, n=37). Blood flow through a secundum atrial septal defect as assessed by PC-MRI (n=24) overestimated the shunt compared with the difference between pulmonary and aortic flows. The mean difference between 3 repeated PC-MRI measurements in each location was 5.3% (SD ±4.0%, n=522), demonstrating good precision. The interobserver variability was low. The accuracy of PC-MRI was confirmed by in vitro experiments. Conclusions—Determination of ˙Qp/˙Qs by PC-MRI in children is quick, safe, and reliable compared with oximetry. Systemic venous flow can be quantified by PC-MRI, whereas through-plane shunt measurement within an atrial septal defect is inaccurate.

1H metabolite relaxation times at 3.0 tesla: Measurements of T1 and T2 values in normal brain and determination of regional differences in transverse relaxation

To measure 1H relaxation times of cerebral metabolites at 3 T and to investigate regional variations within the brain.

Dual-Source Parallel Radiofrequency Excitation Body MR Imaging Compared with Standard MR Imaging at 3.0 T: Initial Clinical Experience

PURPOSE To prospectively compare the image quality and homogeneity of magnetic resonance (MR) images obtained by using a dual-source parallel radiofrequency (RF) excitation body MR imaging system with parallel transmission and independent RF shimming with the image quality and homogeneity of single-source MR images obtained by using standard sequences for routine clinical use in patients at 3.0 T. MATERIALS AND METHODS After institutional review board approval and informed patient consent were obtained, a dual-source parallel RF excitation 3.0-T MR system with independent RF shimming and parallel transmission technology was used to examine 28 patients and was compared with a standard 3.0-T MR system with single RF transmission. The RF power was distributed to the independent ports of the system body coil by using two RF transmission sources with full software control, enabling independent control of the phase and amplitude of the RF waveforms. Axial T2-weighted fast spin-echo (SE) and diffusion-weighted (DW) liver images, axial T2-weighted fast SE pelvic images, and sagittal T1- and T2-weighted fast SE spinal images were obtained by using dual- and single-source RF excitation. Two radiologists independently evaluated the images for homogeneity and image quality. Statistical significance was calculated by using the nonparametric Wilcoxon signed rank test. Interobserver agreement was determined by using Cohen kappa and Kendall tau-b tests. RESULTS Image quality comparisons revealed significantly better results with dual-source rather than single-source RF excitation at T2-weighted liver MR imaging (P = .001, kappa = 1.00) and better results at DW liver imaging at a statistical trend level (P = .066, tau-b > 0.7). Owing to reduced local energy deposition, fewer acquisitions and shorter repetition times could be implemented with dual-source RF excitation pelvic and spinal MR imaging, with image acquisition accelerating by 18%, 33%, and 50% compared with the acquisitions with single-source RF excitation. Image quality did not differ significantly between the two MR techniques (P > .05, tau-b > 0.5). CONCLUSION Dual-source parallel RF excitation body MR imaging enables reduced dielectric shading, improved homogeneity of the RF magnetic induction field, and accelerated imaging at 3.0 T.

Improved in vivo detection of cortical lesions in multiple sclerosis using double inversion recovery MR imaging at 3 Tesla

ObjectiveTo investigate the impact of a higher magnetic field strength of 3 Tesla (T) on the detection rate of cortical lesions in multiple sclerosis (MS) patients, in particular using a dedicated double inversion recovery (DIR) pulse sequence.MethodsThirty-four patients with clinically isolated syndromes or definite MS were included. All patients underwent magnetic resonance imaging (MRI) at 1.5 T and 3 T, including T2-weighted turbo spin echo (TSE), fluid-attenuated inversion recovery (FLAIR) and DIR sequences. All images were analysed for focal lesions categorised according to their anatomical location.ResultsThe total number of detected lesions was higher at 3 T across all pulse sequences. We observed significantly higher numbers of lesions involving the cortex at 3 T using a DIR sequence. DIR at 3 T showed 192% more pure intracortical (p < 0.001) and 30% more mixed grey matter-white matter lesions (p = 0.008). No significant increase in cortical lesions could be detected on the FLAIR and T2-weighted images. Using the T2-weighted and FLAIR sequences, significantly more lesions could be detected at 3 T in the infratentorial, periventricular and juxtacortical white matter.ConclusionDIR brain MR imaging at 3 T substantially improves the sensitivity of the detection of cortical lesions compared with the standard magnetic field strength of 1.5 T.

Do T2-weighted pulse sequences help with the differential diagnosis of enhancing lesions in dynamic breast MRI?

In this study, our purpose was to determine whether T2‐weighted images are a useful diagnostic adjunct for lesion characterization in dynamic breast MRI. On a 1.5‐T system, 205 enhancing benign and malignant breast tumors were examined. The standardized protocol consisted of a T2‐weighted turbo spin echo (TSE) pulse sequence with and without spectral fat suppression (SPIR), followed by a two‐dimensional dynamic series with subtraction postprocessing. In 59 cases, T2*‐weighted gradient‐echo images also were obtained. Two independent radiologists visually rated the lesions (101 malignant, 104 benign) as having either a low or a high signal with respect to the adjacent glandular tissue. To assess age dependency of lesion enhancement velocities and T2‐TSE signal intensities, we compared the results for patients at or below the age of 50 (group A), between 40 and 50 (group B), and beyond the age of 50 (group C). In T2‐weighted TSE images, breast cancers were iso‐ or hypointense with respect to breast parenchyma in 87% of cases, whereas fibroadenomas were hyperintense in 71%. Visual assessment of lesion appearance in T2‐weighted TSE images allowed to distinguish between fibroadenomas and breast cancers, with a respective sensitivity, specificity, positive predictive value, and negative predictive value of 72%, 75%, 46%, and 90% for young patients; 94%, 66%, 78%, and 89% for the patients between 40 and 50; and 89%, 62%, 85%, and 68% for the patients over 50 years of age. No significant difference was found for the distribution of signal intensities of lesions in T2*‐weighted images or in fat‐suppressed images. In a contrast‐enhancing breast lesion, careful analysis of T2‐weighted TSE images can improve differential diagnosis. The accuracy of this criterion varies with age. J. Magn. Reson. Imaging 1999;9:187–196.

Diffusion-weighted whole-body MR imaging with background body signal suppression: a feasibility study at 3.0 Tesla

The purpose was to provide a diffusion-weighted whole-body magnetic resonance (MR) imaging sequence with background body signal suppression (DWIBS) at 3.0 Tesla. A diffusion-weighted spin-echo echo-planar imaging sequence was combined with the following methods of fat suppression: short TI inversion recovery (STIR), spectral attenuated inversion recovery (SPAIR), and spectral presaturation by inversion recovery (SPIR). Optimized sequences were implemented on a 3.0- and a 1.5-Tesla system and evaluated in three healthy volunteers and six patients with various lesions in the neck, chest, and abdomen on the basis of reconstructed maximum intensity projection images. In one patient with metastases of malignant melanoma, DWIBS was compared with 18F-fluorodeoxyglucose positron emission tomography (FDG-PET). Good fat suppression for all regions and diagnostic image quality in all cases could be obtained at 3.0 Tesla with the STIR method. In comparison with 1.5 Tesla, DWIBS images at 3.0 Tesla were judged to provide a better lesion-to-bone tissue contrast. However, larger susceptibility-induced image distortions and signal intensity losses, stronger blurring artifacts, and more pronounced motion artifacts degraded the image quality at 3.0 Tesla. A good correlation was found between the metastases as depicted by DWIBS and those as visualized by FDG-PET. DWIBS is feasible at 3.0 Tesla with diagnostic image quality.

Rapid Left-to-Right Shunt Quantification in Children by Phase-Contrast Magnetic Resonance Imaging Combined With Sensitivity Encoding (SENSE)

Background—Parallel imaging by sensitivity encoding (SENSE) may considerably reduce scan time in MRI. For rapid flow quantification in children with congenital heart disease, we evaluated phase-contrast MRI (PC-MRI) techniques combined with SENSE. Methods and Results—In 22 pediatric patients (mean age, 7.2±6.2 years) with cardiac left-to-right shunt, blood flow rate in the pulmonary artery (Qp) and ascending aorta (Qs) and flow ratio Qp/Qs were determined by PC-MRI with SENSE reduction-factor 2 and 3 (SF-2 and SF-3). Additionally, we used PC-MRI with higher spatial in-plane resolution (1.6×2.1 versus 2.3×3.1 mm) with and without SF-3. Results were compared with a recently validated standard PC-MRI protocol and tested in vitro using a pulsatile flow phantom. Reduction of signal averages from 2 to 1 and application of SENSE accelerated flow measurements by a factor of 3.5 (5.2) using PC-MRI with SF-2 (SF-3) compared with standard PC-MRI. For blood flow rate through the pulmonary artery and aorta, as well as for the Qp/Qs ratio we found negligible differences of ±3%, lower limits of agreement (mean±2 SD) of −7% to −18%, and upper limits of agreement (mean±2 SD) of +3 to +24%, demonstrating good agreement with standard PC-MRI. Mean Qp/Qs ratio by standard PC-MRI was 1.69±0.45 (range, 1.27 to 2.79). Interobserver variability was low, and high accuracy was confirmed in vitro for all protocols. Conclusions—PC-MRI for flow quantitation may be combined with SENSE to achieve a substantive reduction of scanning time. In children with left-to-right shunt, Qp/Qs quantification is possible by PC-MRI+SF-3 in <60 seconds. Use of higher in-plane resolution did not improve measurement results.

Flow Volume and Shunt Quantification in Pediatric Congenital Heart Disease by Real-Time Magnetic Resonance Velocity Mapping A Validation Study

Background—Flow quantification in real time by phase-contrast MRI (PC-MRI) may provide unique hemodynamic information in congenital heart disease, but available techniques have important limitations. We sought to validate a novel real-time magnetic resonance flow sequence in children. Methods and Results—In 14 pediatric patients (mean age 5.2±2.0 years) with cardiac left-to-right shunt, pulmonary (Qp) and aortic (Qs) flow rates were determined by nontriggered free-breathing real-time PC-MRI with single-shot echo-planar imaging combined with sensitivity encoding, which yielded 25 phase images per second at 2.7×2.7-mm in-plane resolution (field of view 30×34 cm2). Over a 9.5-second period that included 2 to 5 respiratory cycles, 16.6±2.6 subsequent stroke volumes (range 13 to 22) were acquired in each vessel. Results were compared with conventional retrospectively ECG-gated PC-MRI. Mean Qp/Qs by conventional PC-MRI was 1.91±0.64, and it was 1.94±0.68 (mean±SD) by real-time PC-MRI. For blood flow rate through pulmonary artery and aorta, we found differences of 2% to 3% (Bland-Altman analysis), with lower limits of agreement of −11% to −13% (mean−2 SD) and upper limits of 18% to 19% (mean±2 SD), which demonstrated good agreement between both methods. Mean difference for Qp/Qs was 1%, with limits of agreement ranging between −18% and 22% (mean±2 SD). High repeatability but some flow overestimation was observed in vitro (pulsatile flow phantom) with real-time PC-MRI, whereas conventional PC-MRI was accurate. Beat-to-beat stroke-volume variation was 6.1±2.3% in vivo and 3.7±0.3% in vitro. Conclusions—Beat-to-beat quantification of pulmonary and aortic flows and hence left-to-right shunt within a few seconds is reliable by nontriggered real-time PC-MRI with echo-planar imaging and sensitivity encoding. Good spatial/temporal resolution and a large field of view may render the sequence valuable for multiple applications in congenital heart disease.

Peripheral MR Angiography with Blood Pool Contrast Agent: Prospective Intraindividual Comparative Study of High-Spatial-Resolution Steady-State MR Angiography versus Standard-Resolution First-Pass MR Angiography and DSA

PURPOSE To prospectively compare the accuracy of high-spatial-resolution steady-state magnetic resonance (MR) angiography with standard-resolution first-pass MR angiography in the lower extremities, with digital subtraction angiography (DSA) as the reference standard. MATERIALS AND METHODS Institutional ethics committee approval and written informed consent were obtained. Twenty-seven patients (16 men, 11 women; mean age, 64.4 years +/- 14.8 [standard deviation]; range, 26-87 years) suspected of having or known to have peripheral arterial disease underwent first-pass and steady-state MR angiography and DSA. First-pass and steady-state MR angiography were performed in the same patient in the same session and with the same dose of blood pool contrast agent. The most severe stenosis grade of each evaluated segment was measured; sensitivity, specificity, and positive and negative predictive values were calculated at first-pass and steady-state MR angiography, with DSA as the reference standard. The kappa coefficient was used to measure the agreement between first-pass MR angiography, steady-state MR angiography, and DSA. RESULTS A total of 334 arterial segments were available for intraindividual comparison of first-pass MR angiography, steady-state MR angiography, and DSA in 27 patients. In 20 (74%) of 27 patients, the stenosis grade of at least one of the evaluated vessels differed at steady-state MR angiography from that at first-pass MR angiography. In total, stenosis grade was judged as higher at first-pass MR angiography than at DSA (overestimation) in 28 of 334 segments and as lower (underestimation) in 15 of 334 segments. The stenosis grade as judged at steady-state MR angiography matched with that at DSA in 334 of 334 vessel segments. CONCLUSION High-spatial-resolution steady-state MR angiography allowed for better agreement with DSA regarding stenosis grade in patients with arterial disease compared with standard-resolution arterial-phase first-pass MR angiography.

4D time-resolved MR angiography with keyhole (4D-TRAK): More than 60 times accelerated MRA using a combination of CENTRA, keyhole, and SENSE at 3.0T†

To present a new 4D method that is designed to provide high spatial resolution MR angiograms at subsecond temporal resolution by combining different techniques of view sharing with parallel imaging at 3.0T.