Andreas Max Weng

CAIPIRINHA accelerated SSFP imaging

Exciting multiple slices at the same time, “controlled aliasing in parallel imaging results in higher acceleration” (CAIPIRINHA) and “phase‐offset multiplanar” have shown to be very effective techniques in 2D multislice imaging. Being provided with individual rf phase cycles, the simultaneously excited slices are shifted with respect to each other in the FOV and, thus, can be easily separated. For SSFP sequences, however, similar rf phase cycles are required to maintain the steady state, impeding a straightforward application of phase‐offset multiplanar or controlled aliasing in parallel imaging results in higher acceleration. In this work, a new flexible concept for applying the two multislice imaging techniques to SSFP sequences is presented. Linear rf phase cycles are introduced providing both in one, the required shift between the slices and steady state in each slice throughout the whole measurement. Consequently, the concept is also appropriate for real‐time and magnetization prepared imaging. Steady state properties and shifted banding behavior of the new phase cycles were investigated using simulations and phantom experiments. Moreover, the concept was applied to perform whole heart myocardial perfusion SSFP imaging as well as real‐time and cine SSFP imaging with increased coverage. Showing no significant penalties in SNR or image quality, the results successfully demonstrate the general applicability of the concept. Magn Reson Med, 2010.

Vertebral Compression Fractures: Third-Generation Dual-Energy CT for Detection of Bone Marrow Edema at Visual and Quantitative Analyses

Purpose To assess the diagnostic performance of a third-generation dual-energy computed tomographic (CT) virtual noncalcium (VNCa) technique for detection of traumatic bone marrow edema in patients with vertebral compression fractures. Materials and Methods This prospective study was approved by the institutional review board. Informed consent was obtained from all participants. Twenty-two consecutive patients with 37 morphologic vertebral fractures were studied between October 2015 and May 2016. All patients underwent dual-energy CT (90 kV and 150 kV with a tin filter) and 3-T magnetic resonance (MR) imaging. Two independent readers visually evaluated all vertebral bodies (n = 163) for the presence of abnormal bone marrow attenuation on VNCa images by using color-coded maps and performed a quantitative analysis of CT numbers on VNCa images. MR images served as the reference standard. CT numbers were subjected to receiver operating characteristic analysis to calculate cutoff values. Results In the visual analysis, VNCa images had an overall sensitivity of 64.0%, specificity of 99.3%, accuracy of 93.9%, positive predictive value of 94.1%, and negative predictive value of 93.8%. The interobserver agreement was excellent (κ = 0.85). CT numbers obtained from VNCa images were significantly different in vertebral bodies with and without edema (P < .001). Receiver operating characteristic analysis revealed an area under the curve of 0.922. A cutoff value of -47 provided sensitivity of 92.0%, specificity of 82.6%, accuracy of 84.0%, positive predictive value of 48.9%, and negative predictive value of 98.3% for the differentiation of edematous vertebral bodies. Conclusion Visual and quantitative analyses of dual-energy VNCa images showed excellent diagnostic performance for assessing traumatic bone marrow edema in vertebral compression fractures.

Free breathing cardiac real-time cine MR without ECG triggering

The increasing frequency of LV functional MRI studies demands for faster methods and for more comfort for the patient. We tested, whether real-time (RT) non ECG triggered MRI allows a considerable shortening of examination time in high reproducibility. RT and standard ECG-triggered breathhold cine MRI was acquired in 9 volunteers and 21 patients. Differences between both methods were assessed by Bland-Altman analyses including variability studies. Compared to standard cine MRI, RT decreased data acquisition time by more than the factor of ten. RT produced comparable results (e.g. EF in %: +0.67 [-5.63, 6.97]) except for a slight overestimation of LV mass. Interstudy and intraobserver variability of RT cine showed a low variability. Consequently, free-breathing RT cine proved to be a reliable and suitable tool for clinical routine and may be particularly relevant in patients with sub-optimal breath-holding ability and arrhythmia.

High resolution myocardial first-pass perfusion imaging with extended anatomic coverage

To evaluate and to compare Parallel Imaging and Compressed Sensing acquisition and reconstruction frameworks based on simultaneous multislice excitation for high resolution contrast‐enhanced myocardial first‐pass perfusion imaging with extended anatomic coverage.

Quantitative myocardial perfusion imaging with a MR cold pressor test

The response of myocardial blood flow to sympathetic stimulation with cold is modulated by endothelium‐related factors. As endothelial dysfunction is an early step in patients with coronary artery disease, the aim of this study was to establish a cold pressor test (CPT) setting for quantitative analysis of myocardial perfusion in a MR scanner. First pass perfusion studies were performed in 10 healthy volunteers using a 1.5 T MR scanner with a multislice steady state free precession perfusion trueFISP sequence in prebolus technique (1 cc/4 cc gadobenate dimeglumine). MR‐CPT was established using an over head ice‐water bath of the left hand. First pass perfusion imaging was started after 1 min to assure an adequate stimulus followed by a second series after 15 min to evaluate the rest perfusion. After motion correction images were segmented with an adapted, automated tool, myocardial contours were determined. Perfusion was quantitatively evaluated after contamination and baseline correction by deconvolution with the arterial input function using an exponential function model as residuum. All data could be evaluated. Mean myocardial perfusion rose from 0.61 ± 0.22 cc/g/min at rest to 1.15 ± 0.34 cc/g/min under CPT. MR myocardial perfusion values show a comparable increase under CPT as published positron emission tomography data. Consequently, CPT for the presence of endothelial dysfunction is feasible in the MR environment. Magn Reson Med, 2011.

Non-invasive Determination of Myocardial Lipid Content in Fabry Disease by 1H-MR Spectroscopy

PURPOSE In Fabry disease (FD), a progressive deposition of sphingolipids is reported in different organs. The present study applied 1H magnetic resonance spectroscopy (MRS) to investigate the myocardial lipid content in FD. MATERIALS AND METHODS In patients (PTS, n = 15) with genetically proven FD, 1H MRS of the heart was acquired in the same examination as routine cardiac cine and late enhancement MR imaging. Healthy volunteers (n = 11) without history of cardiac disease served as control (CTL). Myocardial triglycerides in vivo were quantified in 1H MRS. Left ventricular (LV) ejection fraction (EF) and late enhancement were assessed for the determination of LV systolic function, and onset or absence of myocardial fibrosis. RESULTS All 1H MRS revealed resonances for intramyocardial triglycerides. Clinical parameters, e.g. EF (PTS 64 ± 2 % vs. CTL 61 ± 1 %) were similar in PTS and CTL or showed a non-significant trend (LV mass). Apart from a single patient with elevated myocardial triglycerides, no significant impact of Fabry disease on the triglyceride/water resonance ratio (PTS 0.47 ± 0.11 vs. CTL 0.52 ± 0.11 %) was observed in our patient cohort. CONCLUSION A comprehensive cardiac evaluation of morphology, function as well as metabolism in Fabry PTS with suspected cardiac involvement is feasible in a single examination. No significant effect of myocardial triglyceride deposition could be observed in patients. The remarkably high myocardial triglyceride content in one patient with advanced FD warrants further studies in PTS with an extended history of the disease.

Self-gated Non–Contrast-enhanced Functional Lung MR Imaging for Quantitative Ventilation Assessment in Patients with Cystic Fibrosis

Purpose To assess the clinical feasibility of self-gated non-contrast-enhanced functional lung (SENCEFUL) magnetic resonance (MR) imaging for quantitative ventilation (QV) imaging in patients with cystic fibrosis (CF). Materials and Methods Twenty patients with CF and 20 matched healthy volunteers underwent functional 1.5-T lung MR imaging with the SENCEFUL imaging approach, in which a two-dimensional fast low-angle shot sequence is used with quasi-random sampling. The lungs were manually segmented on the ventilation-weighted images to obtain QV measurements, which were compared between groups. QV values of the patients were correlated with results of pulmonary function testing. Three radiologists rated the images for presence of ventilation deficits by means of visual inspection. Mann-Whitney U tests, receiver operating characteristic analyses, Spearman correlations, and Gwet agreement coefficient analyses were used for statistical analysis. Results QV of the entire lungs was lower for patients with CF than for control subjects (mean ± standard deviation, 0.09 mL/mL ± 0.03 vs 0.11 mL/mL ± 0.03, respectively; P = .007). QV ratios of upper to lower lung halves were lower in patients with CF than in control subjects (right, 0.84 ± 0.2 vs 1.16 ± 0.2, respectively [P < .001]; left, 0.88 ± 0.3 vs 1.11 ± 0.1, respectively [P = .017]). Accordingly, ventilation differences between the groups were larger in the upper halves (Δ = 0.04 mL/mL, P ≤ .001-.002). QV values of patients with CF correlated with forced vital capacity (r = 0.7; 95% confidence interval [CI]: 0.21, 0.91), residual volume (static hyperinflation, r = -0.8; 95% CI: -0.94, 0.42), and forced expiratory volume in 1 second (airway obstruction, r = 0.7; 95% CI: 0.21, 0.91). Disseminated small ventilation deficits were the most frequent involvement pattern, present in 40% of the functional maps in CF versus 8% in the control subjects (P < .001). Conclusion SENCEFUL MR imaging is feasible for QV assessment. Less QV, especially in upper lung parts, and correlation to vital capacity and to markers for hyperinflation and airway obstruction were found in patients with CF.

Comparing the MRI-based Goutallier Classification to an experimental quantitative MR spectroscopic fat measurement of the supraspinatus muscle

BackgroundThe Goutallier Classification is a semi quantitative classification system to determine the amount of fatty degeneration in rotator cuff muscles. Although initially proposed for axial computer tomography scans it is currently applied to magnet-resonance-imaging-scans. The role for its clinical use is controversial, as the reliability of the classification has been shown to be inconsistent. The purpose of this study was to compare the semi quantitative MRI-based Goutallier Classification applied by 5 different raters to experimental MR spectroscopic quantitative fat measurement in order to determine the correlation between this classification system and the true extent of fatty degeneration shown by spectroscopy.MethodsMRI-scans of 42 patients with rotator cuff tears were examined by 5 shoulder surgeons and were graduated according to the MRI-based Goutallier Classification proposed by Fuchs et al. Additionally the fat/water ratio was measured with MR spectroscopy using the experimental SPLASH technique. The semi quantitative grading according to the Goutallier Classification was statistically correlated with the quantitative measured fat/water ratio using Spearman’s rank correlation.ResultsStatistical analysis of the data revealed only fair correlation of the Goutallier Classification system and the quantitative fat/water ratio with R = 0.35 (p < 0.05). By dichotomizing the scale the correlation was 0.72. The interobserver and intraobserver reliabilities were substantial with R = 0.62 and R = 0.74 (p < 0.01).ConclusionThe correlation between the semi quantitative MRI based Goutallier Classification system and MR spectroscopic fat measurement is weak. As an adequate estimation of fatty degeneration based on standard MRI may not be possible, quantitative methods need to be considered in order to increase diagnostic safety and thus provide patients with ideal care in regard to the amount of fatty degeneration. Spectroscopic MR measurement may increase the accuracy of the Goutallier classification and thus improve the prediction of clinical results after rotator cuff repair. However, these techniques are currently only available in an experimental setting.

Multiple Myeloma and Dual-Energy CT: Diagnostic Accuracy of Virtual Noncalcium Technique for Detection of Bone Marrow Infiltration of the Spine and Pelvis

Purpose To determine the diagnostic performance of dual-energy computed tomography (CT) for detection of bone marrow (BM) infiltration in patients with multiple myeloma by using a virtual noncalcium (VNCa) technique. Materials and Methods In this prospective study, 34 consecutive patients with multiple myeloma or monoclonal gammopathy of unknown significance sequentially underwent dual-energy CT and magnetic resonance (MR) imaging of the axial skeleton. Two independent readers visually evaluated standard CT and color-coded VNCa images for the presence of BM involvement. MR imaging served as the reference standard. Analysis on the basis of the region of interest (ROI) of VNCa CT numbers of infiltrated (n = 75) and normal (n = 170) BM was performed and CT numbers were subjected to receiver operating characteristic analysis to calculate cutoff values. Results In the visual analysis, VNCa images had an overall sensitivity of 91.3% (21 of 23), specificity of 90.9% (10 of 11), accuracy of 91.2% (31 of 34), positive predictive value of 95.5% (21 of 22), and a negative predictive value of 83.3% (10 of 12). ROI-based analysis of VNCa CT numbers showed a significant difference between infiltrated and normal BM (P < .001). Receiver operating characteristic analysis revealed an area under the curve of 0.978. A cutoff of -44.9 HU provided a sensitivity of 93.3% (70 of 75), specificity of 92.4% (157 of 170), accuracy of 92.7% (227 of 245), positive predictive value of 84.3% (70 of 83), and negative predictive value of 96.9% (157 of 162) for the detection of BM infiltration. Conclusion Visual and ROI-based analyses of dual-energy VNCa images had excellent diagnostic performance for assessing BM infiltration in patients with multiple myeloma with precision comparable to that of MR imaging.

Impact of advanced modeled iterative reconstruction on interreader agreement in coronary artery measurements

OBJECTIVES To evaluate the influence of advanced modeled iterative reconstruction (ADMIRE) on coronary artery computed tomography angiography (cCTA) measurements in comparison to filtered back projection (FBP). MATERIAL AND METHODS Phantom scans and coronary CTA studies of 27 patients were acquired with a third generation dual-source CT scanner. Images were reconstructed using FBP and ADMIRE. Phantom measurements were used as reference standard. In patient studies, representative axial slices of each coronary artery segment without (n=308) and with coronary plaques (n=40) were assessed in identical positions for comparison of FBP and ADMIRE reconstructions. Image analyses included quality assessment, phantom and coronary artery measurements, plaque analysis, and interreader agreement of two independent and blinded readers. RESULTS Mean image noise was lower on ADMIRE reconstructions with 31.3±9.9 HU compared to 55.9±15.7 HU on FBP reconstructions (p<0.001). Measurement precision and interreader agreement of both observers were assessed satisfactorily on phantom images in comparison to the full width half maximum method. In patients, correlation of lumen diameters of both observers improved using ADMIRE with a Pearsons r=0.987 (95% confidence interval [CI], 0.983-0.989; p<0.001) compared to FBP images with r=0.939 (95% CI, 0.924-0.951; p<0.001). Applying ADMIRE, agreement of both observers for lumen diameter measurements significantly increased (p<0.001). This was also observed for the degree of stenosis (p<0.001) with r=0.560 using FBP (95% CI, 0.301-0.742) and with r=0.818 using ADMIRE (95% CI, 0.680-0.900). Plaque density measurements correlated closely with a Pearsons r of 0.951 in FBP (95% CI, 0.909-0.974) and 0.967 in ADMIRE (95% CI, 0.939-0.983). CONCLUSIONS Advanced modeled iterative reconstruction significantly improves coronary artery assessment in coronary CTA in comparison to FBP by improved image quality due to image noise removal. This renders improved interobserver agreement for coronary lumen diameter and degree of stenosis measurements without influencing mean plaque attenuation.