Michael Zenge

Respiratory self‐navigation for whole‐heart bright‐blood coronary MRI: Methods for robust isolation and automatic segmentation of the blood pool

Free‐breathing three‐dimensional whole‐heart coronary MRI is a noninvasive alternative to X‐ray coronary angiography. However, the existing navigator‐gated approaches do not meet the requirements of clinical practice, as they perform with suboptimal accuracy and require prolonged acquisition times. Self‐navigated techniques, applied to bright‐blood imaging sequences, promise to detect the position of the blood pool directly in the readouts acquired for imaging. Hence, the respiratory displacement of the heart can be calculated and used for motion correction with high accuracy and 100% scan efficiency. However, additional bright signal from the chest wall, spine, arms, and liver can render the isolation of the blood pool impossible. In this work, an innovative method based on a targeted combination of the output signals of an anterior phased‐array surface coil is implemented to efficiently suppress such additional bright signal. Furthermore, an algorithm for the automatic segmentation of the blood pool is proposed. Robust self‐navigation is achieved by cross‐correlation. These improvements were integrated into a three‐dimensional radial whole‐heart coronary MRI sequence and were compared with navigator‐gated imaging in vivo. Self‐navigation was successful in all cases and the acquisition time was reduced up to 63%. Equivalent or slightly superior image quality, vessel length, and sharpness were achieved. Magn Reson Med, 2012.

Spiral Phyllotaxis: The Natural Way to Construct a 3D Radial Trajectory in MRI

While radial 3D acquisition has been discussed in cardiac MRI for its excellent results with radial undersampling, the self‐navigating properties of the trajectory need yet to be exploited. Hence, the radial trajectory has to be interleaved such that the first readout of every interleave starts at the top of the sphere, which represents the shell covering all readouts. If this is done sub‐optimally, the image quality might be degraded by eddy current effects, and advanced density compensation is needed. In this work, an innovative 3D radial trajectory based on a natural spiral phyllotaxis pattern is introduced, which features optimized interleaving properties: ( 1 ) overall uniform readout distribution is preserved, which facilitates simple density compensation, and ( 2 ) if the number of interleaves is a Fibonacci number, the interleaves self‐arrange such that eddy current effects are significantly reduced. These features were theoretically assessed in comparison with two variants of an interleaved Archimedean spiral pattern. Furthermore, the novel pattern was compared with one of the Archimedean spiral patterns, with identical density compensation, in phantom experiments. Navigator‐gated whole‐heart coronary imaging was performed in six healthy volunteers. High reduction of eddy current artifacts and overall improvement in image quality were achieved with the novel trajectory. Magn Reson Med, 2011.

Compressed sensing single-breath-hold CMR for fast quantification of LV function, volumes, and mass.

OBJECTIVES The purpose of this study was to compare a novel compressed sensing (CS)-based single-breath-hold multislice magnetic resonance cine technique with the standard multi-breath-hold technique for the assessment of left ventricular (LV) volumes and function. BACKGROUND Cardiac magnetic resonance is generally accepted as the gold standard for LV volume and function assessment. LV function is 1 of the most important cardiac parameters for diagnosis and the monitoring of treatment effects. Recently, CS techniques have emerged as a means to accelerate data acquisition. METHODS The prototype CS cine sequence acquires 3 long-axis and 4 short-axis cine loops in 1 single breath-hold (temporal/spatial resolution: 30 ms/1.5 × 1.5 mm(2); acceleration factor 11.0) to measure left ventricular ejection fraction (LVEF(CS)) as well as LV volumes and LV mass using LV model-based 4D software. For comparison, a conventional stack of multi-breath-hold cine images was acquired (temporal/spatial resolution 40 ms/1.2 × 1.6 mm(2)). As a reference for the left ventricular stroke volume (LVSV), aortic flow was measured by phase-contrast acquisition. RESULTS In 94% of the 33 participants (12 volunteers: mean age 33 ± 7 years; 21 patients: mean age 63 ± 13 years with different LV pathologies), the image quality of the CS acquisitions was excellent. LVEF(CS) and LVEF(standard) were similar (48.5 ± 15.9% vs. 49.8 ± 15.8%; p = 0.11; r = 0.96; slope 0.97; p < 0.00001). Agreement of LVSV(CS) with aortic flow was superior to that of LVSV(standard) (overestimation vs. aortic flow: 5.6 ± 6.5 ml vs. 16.2 ± 11.7 ml, respectively; p = 0.012) with less variability (r = 0.91; p < 0.00001 for the CS technique vs. r = 0.71; p < 0.01 for the standard technique). The intraobserver and interobserver agreement for all CS parameters was good (slopes 0.93 to 1.06; r = 0.90 to 0.99). CONCLUSIONS The results demonstrated the feasibility of applying the CS strategy to evaluate LV function and volumes with high accuracy in patients. The single-breath-hold CS strategy has the potential to replace the multi-breath-hold standard cardiac magnetic resonance technique.

Peripheral magnetic resonance angiography (MRA) with continuous table movement at 3.0 T: initial experience compared with step-by-step MRA.

Purpose:To compare a standard step-by-step and a newly developed continuous table movement (CTM) technique for peripheral magnetic resonance angiography (MRA) at a 3.0-Tesla MR system equipped with a matrix coil system. Materials and Methods:We included 14 consecutive patients referred for peripheral MRA with clinical symptoms of peripheral arterial occlusive disease Fontaines stages II–IV. All of them underwent both step-by-step MRA and CTM-MRA in one session. Patients with impaired renal function (calculated glomerular filtration rate <30 mL/min) were not included. All examinations were performed on a 3.0-Tesla MR system. Maximal contrast agent volume was 31.5 mL (1.5 mL testbolus, 15 mL/MRA technique). For both techniques the same biphasic CA injection protocol was used, first 8 mL were injected at a flow rate of 1.5 mL/s directly followed by 7 mL at 0.8 mL/s again followed by 25 mL of saline also at 0.8 mL/s. Spatial resolution of the CTM-MRA datasets was technically limited to 1.2 mm3, step-by-step MRA reached 1.4 × 1.1 × 1.2 mm3 in the abdominal station, 0.9 × 0.9 × 0.9 mm3 in the most distal calf station. First CTM-MRA datasets were read and findings thereafter correlated with the step-by-step MRA datasets. Examination time of both examinations were recorded and compared. Results:All datasets could be evaluated. The first 4 CTM-MRA cases were limited by incorrect timing in the most distal vessels obscuring distinct atherosclerotic changes of those vessels. Because of the absence of multiple localizers and subtraction masks examination time was considerably shorter when using the CTM-MRA technique. Relevant findings that were detected by the step-by-step MRA were also detected by CTM-MRA. Conclusion:MRA with CTM is an easy applicable technique for imaging peripheral vessels without the need for planning different steps and field of view positioning, thereby reducing examination time considerably. However, the slightly reduced spatial resolution compared with standard step-by-step MRA is a drawback especially in the most distal calf vessels.

Reduction of respiratory motion artifacts for free-breathing whole-heart coronary MRA by weighted iterative reconstruction

To combine weighted iterative reconstruction with self‐navigated free‐breathing coronary magnetic resonance angiography for retrospective reduction of respiratory motion artifacts.

Highly undersampled contrast‐enhanced MRA with iterative reconstruction: Integration in a clinical setting

To integrate, optimize, and evaluate a three‐dimensional (3D) contrast‐enhanced sparse MRA technique with iterative reconstruction on a standard clinical MR system.

Is there an optimal respiratory reference position for self‐navigated whole‐heart coronary MR angiography?

To test the direct influence of the reference respiratory position on image quality for self‐navigated whole‐heart coronary MRI.

Three-dimensional MR Cholangiopancreatography in a Breath Hold with Sparsity-based Reconstruction of Highly Undersampled Data

Purpose To develop a three-dimensional breath-hold (BH) magnetic resonance (MR) cholangiopancreatographic protocol with sampling perfection with application-optimized contrast using different flip-angle evolutions (SPACE) acquisition and sparsity-based iterative reconstruction (SPARSE) of prospectively sampled 5% k-space data and to compare the results with conventional respiratory-triggered (RT) acquisition. Materials and Methods This HIPAA-compliant prospective study was institutional review board approved. Twenty-nine patients underwent conventional RT SPACE and BH-accelerated SPACE acquisition with 5% k-space sampling at 3 T. Spatial resolution and other parameters were matched when possible. BH SPACE images were reconstructed by enforcing joint multicoil sparsity in the wavelet domain (SPARSE-SPACE). Two board-certified radiologists independently evaluated BH SPARSE-SPACE and RT SPACE images for image quality parameters in the pancreatic duct and common bile duct by using a five-point scale. The Wilcoxon signed-rank test was used to compare BH SPARSE-SPACE and RT SPACE images. Results Acquisition time for BH SPARSE-SPACE was 20 seconds, which was significantly (P < .001) shorter than that for RT SPACE (mean ± standard deviation, 338.8 sec ± 69.1). Overall image quality scores were higher for BH SPARSE-SPACE than for RT SPACE images for both readers for the proximal, middle, and distal pancreatic duct, but the difference was not statistically significant (P > .05). For reader 1, distal common bile duct scores were significantly higher with BH SPARSE-SPACE acquisition (P = .036). More patients had acceptable or better overall image quality (scores ≥ 3) with BH SPARSE-SPACE than with RT SPACE acquisition, respectively, for the proximal (23 of 29 [79%] vs 22 of 29 [76%]), middle (22 of 29 [76%] vs 18 of 29 [62%]), and distal (20 of 29 [69%] vs 13 of 29 [45%]) pancreatic duct and the proximal (25 of 28 [89%] vs 22 of 28 [79%]) and distal (25 of 28 [89%] vs 24 of 28 [86%]) common bile duct. Conclusion BH SPARSE-SPACE showed similar or superior image quality for the pancreatic and common duct compared with that of RT SPACE despite 17-fold shorter acquisition time. (©) RSNA, 2016.

Nonenhanced arterial spin labeled carotid MR angiography using three-dimensional radial balanced steady-state free precession imaging

To optimize and preliminarily evaluate a three‐dimensional (3D) radial balanced steady‐state free precession (bSSFP) arterial spin labeled (ASL) sequence for nonenhanced MR angiography (MRA) of the extracranial carotid arteries.

Right ventricular assessment at cardiac MRI: initial clinical experience utilizing an IS-SENSE reconstruction

Cardiac MR is considered the gold standard in assessing RV function. The purpose of this study is to evaluate the clinical utility of an investigational iterative reconstruction algorithm in the quantitative assessment of RV function. This technique has the potential to improve the clinical utility of CMR in the evaluation of RV pathologies, particularly in patients with dyspnea, by shortening acquisition times without adversely influencing imaging performance. Segmented cine images were acquired on 9 healthy volunteers and 29 patients without documented RV pathologies using conventional GRAPPA acquisition with factor 2 acceleration (GRAPPA 2), a spatio-temporal TSENSE acquisition with factor 4 acceleration (TSENSE 4), and iteratively reconstructed Sparse SENSE acquisition with factor 4 acceleration (IS-SENSE 4). 14 subjects were re-analyzed and intraclass correlation coefficients (ICC) were calculated and Bland–Altman plots generated to assess agreement. Two independent reviewers qualitatively scored images. Comparison of acquisition techniques was performed using univariate analysis of variance (ANOVA). Differences in RV EF, BSA-indexed ESV (ESVi), BSA-indexed EDV (EDVi), and BSA-indexed SV (SVi) were shown to be statistically insignificant via ANOVA testing. R2 values for linear regression of TSENSE 4 and IS-SENSE 4 versus GRAPPA 2 were 0.34 and 0.72 for RV-EF, and 0.61 and 0.76 for RV-EDVi. ICC values for intraobserver and interobserver quantification yielded excellent agreement, and Bland–Altman plots assessing agreement were generated as well. Qualitative review yielded small, but statistically significant differences in image quality and noise between TSENSE 4 and IS-SENSE 4. All three techniques were rated nearly artifact free. Segmented imaging acquisitions with IS-SENSE reconstruction and an acceleration factor of 4 accurately and reliably quantitates RV systolic function parameters, while maintaining image quality. TSENSE-4 accelerated acquisitions showed poorer correlation to standard imaging, and inferior interobserver and intraobserver agreement. IS-SENSE has the potential to shorten cine acquisition times by 50 %, improving imaging options in patients with intermittent arrhythmias or difficulties with breath holding.