Showing papers by "Marcel Gutberlet published in 2022"

Examining lung microstructure using 19F MR diffusion imaging in COPD patients

Abstract: To examine the time‐dependent diffusion of fluorinated (19F) gas in human lungs for determination of surface‐to‐volume ratio in comparison to results from hyperpolarized 129Xe and lung function testing in healthy volunteers and patients with chronic obstructive pulmonary disease.

Detection of Ablation Boundaries Using Different MR Sequences in a Swine Liver Model

Abstract: To determine the magnetic resonance (MR) sequences best suited for the assessment of ablation zones after radiofrequency ablation (RFA).Three percutaneous MR-guided RFA of the liver were performed on three swine. Four pre-contrast and two hepatobiliary post-contrast sequences were obtained after ablation. Tissue samples were extracted and stained for nicotinamide adenine dinucleotide diaphorase hydride (NADH) and with hematoxylin and eosin. Post-ablation MR images and NADH slides were segmented to determine the total ablation zone, their Dice similarity coefficient (DSC), and the contrast-to-noise ratio (CNR) of the visible ablation boundary to normal liver tissue.Two distinct layers were combined to determine the ablation zone: an inner layer of coagulation necrosis and an outer layer defined as the peripheral transition zone. Corresponding zones could be found in the MR images as well. Compared to histology, the total area of the MR ablation zone was significantly smaller on the pre-contrast T1 images (p < 0.01) and significantly larger with T2 turbo spin-echo (p = 0.025). No significant difference in size of the ablation zone depiction could be found between histology, post-contrast T1 volumetric interpolated breath-hold examination (VIBE), and post-contrast T1 3D Turboflash (TFL) as well as T2 SPACE images. All sequences but the pre-contrast T1 VIBE sequence showed a DSC above 80% and a high CNR.Post-contrast T1 3DTFL performs best when assessing ablation zones after RFA. Since the sequence requires a long acquisition time, T1 VIBE post-contrast offers the best compromise between acquisition time and estimation accuracy.

Volume‐Controlled 19F MR Ventilation Imaging of Fluorinated Gas

Abstract: 19F MRI of inhaled gas tracers has developed into a promising tool for pulmonary diagnostics. Prior to clinical use, the intersession repeatability of acquired ventilation parameters must be quantified and maximized.

Value of functional lung MRI in long term patient care after lung transplantation.

Abstract: Aim: To evaluate the prognostic utility of phase resolved functional lung (PREFUL)-MRI in predicting chronic lung allograft dysfunction (CLAD) related transplant loss or death in a prospective longitudinal single center study. Methods: PREFUL MRI-derived regional flow­ volume loop (RFVL) parameters of double lung transplant recipients were assessed 6-12 months (baseline) and 3 years post transplantation. Ventilated volume was calculated threshold based (RFVL-VV). Spirometry was carried out at the same day. Calculation of Receiver operating characteristics and subsequent Kaplan-Meier survival analysis was used to compare clinical and MRI parameters in regard to the clinical endpoint (CLAD related transplant loss or death). Results: At baseline MRI, 108 clinically stable patients were compared with 24 patients reaching the clinical endpoint. PREFUL MRI-derived RFVL-VV (cutoff=92.3%, average survival 42.9±1.8 vs. 82.5±1.8 month, Log-Rank P=.02) predicted poorer survival of patients at baseline, while spirometry showed no significantly different survival (P>.05). Evaluating the follow-up MRI (75 stable vs 19 patients reaching the endpoint), % change of RFVL showed poorer survival of patients (cutoff=97.1%, 52.5±5.9 vs. 54.1±0.9 month, P<.0001) as well as % change of FEV₁ (cutoff=60.8%, 47.8±8.2 vs. 53.9±0.9 month, P=.0002). Assessing % change at follow-up, a combined score of PREFUL-MRI with FEV₁ showed a stronger prediction of survival (40.0±9.5 vs. 54.0±0.9 month, Log-Rank P<.0001) than either parameter alone. Conclusion: PREFUL-MRI predicts CLAD related death or transplant loss in a large prospective post lung transplant cohort and may add clinical value in monitoring patients post lung transplantation.

Comparison study of reconstruction algorithms for volumetric necrosis maps from 2D multi-slice GRE thermometry images

Abstract: Cancer is a disease which requires a significant amount of careful medical attention. For minimally-invasive thermal ablation procedures, the monitoring of heat distribution is one of the biggest challenges. In this work, three approaches for volumetric heat map reconstruction (Delauney triangulation, minimum volume enclosing ellipsoids (MVEE) and splines) are presented based on uniformly distributed 2D MRI phase images rotated around the applicator's main axis. We compare them with our previous temperature interpolation method with respect to accuracy, robustness and adaptability. All approaches are evaluated during MWA treatment on the same data sets consisting of 13 ex vivo bio protein phantoms, including six phantoms with simulated heat sink effects. Regarding accuracy, the DSC similarity results show a strong trend towards the MVEE ([Formula: see text]) and the splines ([Formula: see text]) method compared to the Delauney triangulation ([Formula: see text]) or the temperature interpolation ([Formula: see text]). Robustness is increased for all three approaches and the adaptability shows a significant trend towards the initial interpolation method and the splines. To overcome local inhomogeneities in the acquired data, the use of adaptive simulations should be considered in the future. In addition, the transfer to in vivo animal experiments should be considered to test for clinical applicability.

Feasibility of flow-related enhancement brain perfusion MRI

Abstract: Purpose Brain perfusion imaging is of enormous importance for various neurological diseases. Fast gradient-echo sequences offering flow-related enhancement (FREE) could present a basis to generate perfusion-weighted maps. In this study, we obtained perfusion-weighted maps without contrast media by a previously described postprocessing algorithm from the field of functional lung MRI. At first, the perfusion signal was analyzed in fast low-angle shot (FLASH) and balanced steady-state free precession (bSSFP) sequences. Secondly, perfusion maps were compared to pseudo-continuous arterial spin labeling (pCASL) MRI in a healthy cohort. Thirdly, the feasibility of the new technique was demonstrated in a small selected group of patients with metastases and acute stroke. Methods One participant was examined with bSSFP and FLASH sequences at 1.5T and 3T, different flip angles and slice thicknesses. Twenty-five volunteers had bSSFP imaging and pCASL MRI. Three patients with cerebral metastases and one with acute ischemic stroke had bSSFP imaging and were compared to T1 post-contrast images and CT perfusion. Frequency analyses, SNR and perfusion contrast were compared at different flip angles and slice thicknesses. Regional correlations and Sorensen-Dice overlap were calculated in the healthy cohort. Dice overlap of the pathologies in the patient cohort were calculated. Results The bSSFP sequence presented detectable perfusion signal within brain vessel and parenchyma together with superior SNR compared to FLASH. Perfusion contrast and its corticomedullary differentiation increased with flip angle. Mean regional correlation was 0.36 and highly significant between FREE maps and pCASL and grey and white matter Dice match were 72% and 60% in the healthy cohort. Pathologies presented good overlap between FREE perfusion-weighted and T1 post-contrast images. Conclusion The feasibility of FREE brain perfusion imaging has been shown in a healthy cohort and selected patient cases with brain metastases and acute stroke. The study demonstrates a new approach for non-contrast brain perfusion imaging.

Evaluation of image registration algorithms for 3D phase‐resolved functional lung ventilation magnetic resonance imaging in healthy volunteers and chronic obstructive pulmonary disease patients

Abstract: The purpose of the current study was to assess the influence of the registration algorithms on the repeatability of three‐dimensional (3D) phase‐resolved functional lung (PREFUL) ventilation magnetic resonance imaging (MRI). Twenty‐three healthy volunteers and 10 patients with chronic obstructive pulmonary disease (COPD) underwent 3D PREFUL MRI during tidal breathing. The registration of dynamically acquired data to a fixed image was executed using single‐step, stepwise, and group‐oriented registration (GOREG) approaches. Advanced Normalization Tools (ANTs) and the Forsberg image‐registration package were used for the registration. Image registration algorithms were tested for differences and evaluated by the repeatability analysis of ventilation parameters using coefficient of variation (CoV), intraclass‐correlation coefficient, Bland–Altman plots, and correlation to spirometry. Also, the registration time and image quality were computed for all registration approaches. Very strong to strong correlations (r range: 0.917–0.999) were observed between ventilation parameters derived using various registration approaches. Median CoV values of the cross‐correlation (CC) parameter were significantly lower (all p ≤ 0.0054) for ANTs GOREG compared with single‐step and stepwise ANTs registration. The majority of comparisons between COPD patients and age‐matched healthy volunteers showed agreement among the registration approaches. The repeatability of regional ventilation (RVent)‐based ventilation defect percentage (VDPRVent) and VDPCC was significantly higher (both p ≤ 0.0054) for Forsberg GOREG compared with ANTs GOREG. All 3D PREFUL‐derived ventilation parameters correlated with forced expiratory volume in 1 s (FEV1) and the FEV1/ forced vital capacity (FVC) ratio (all |r| > 0.40, all p < 0.03). The image sharpness of RVent maps was statistically elevated (all p < 0.001) using GOREG compared with single‐step and stepwise registration approaches using ANTs. The best computational performance was achieved with Forsberg GOREG. The GOREG scheme improves the repeatability and image quality of dynamic 3D PREFUL ventilation parameters. Registration time can be ~10‐fold reduced to 9 min using the Forsberg method with equal or even improved repeatability and comparable PREFUL ventilation results compared with the ANTs method.

Adaptive simulation of 3D thermometry maps for interventional MR-guided tumor ablation using Pennes’ bioheat equation and isotherms

Abstract: Minimally-invasive thermal ablation procedures have become clinically accepted treatment options for tumors and metastases. Continuous and reliable monitoring of volumetric heat distribution promises to be an important condition for successful outcomes. In this work, an adaptive bioheat transfer simulation of 3D thermometry maps is presented. Pennes' equation model is updated according to temperature maps generated by uniformly distributed 2D MR phase images rotated around the main axis of the applicator. The volumetric heat diffusion and the resulting shape of the ablation zone can be modelled accurately without introducing a specific heat source term. Filtering the temperature maps by extracting isotherms reduces artefacts and noise, compresses information of the measured data and adds physical a priori knowledge. The inverse heat transfer for estimating values of the simulated tissue and heating parameters is done by reducing the sum squared error between these isotherms and the 3D simulation. The approach is evaluated on data sets consisting of 13 ex vivo bio protein phantoms, including six perfusion phantoms with simulated heat sink effects. Results show an overall average Dice score of 0.89 ± 0.04 (SEM < 0.01). The optimization of the parameters takes 1.05 ± 0.26 s for each acquired image. Future steps should consider the local optimization of the simulation parameters instead of a global one to better detect heat sinks without a priori knowledge. In addition, the use of a proper Kalman filter might increase robustness and accuracy if combined with our method.

4D-flow cardiac magnetic resonance imaging after aortic root replacement with long-valved decellularized aortic homografts: comparison to valve-sparing aortic root replacement and healthy controls

Abstract: Abstract OBJECTIVES Long-valved decellularized aortic homografts (DAH) may be used in young patients to treat aortic valve disease associated with aortic root dilatation, thereby eliminating the need for prosthetic material and anticoagulation. METHODS Thirty-three male subjects in 3 equally sized cohorts were compared: patients following DAH implantation with a median age of 29 years [interquartile range (IQR) 27.5–37.5], patients post-valve-sparing aortic root replacement (VSARR), median 44 years (IQR 31.5–49) and healthy controls, median 33 years (IQR 28–40, P = 0.228). Time-resolved three-dimensional phase-contrast cardiac magnetic resonance imaging was performed to assess maximum blood flow velocity, pulse wave velocity, mechanical energy loss (EL), wall shear stress and flow patterns (vorticity, eccentricity, helicity) in 5 different planes of the aorta. RESULTS The mean time between surgery and cardiovascular magnetic resonance was 2.56 ± 2.0 years in DAH vs 2.67 ± 2.1 in VSARR, P = 0.500. No significant differences in maximum velocity and pulse wave velocity were found between healthy controls and DAH across all planes. Velocity in the proximal aorta was significantly higher in VSARR (182.91 ± 53.91 cm/s, P = 0.032) compared with healthy controls. EL was significantly higher in VSARR in the proximal aorta with 1.85 mW (IQR 1.39–2.95) compared with healthy controls, 1.06 mW (0.91–1.22, P = 0.016), as well as in the entire thoracic aorta. In contrast, there was no significant EL in DAH in the proximal, 1.27 m/W (0.92–1.53, P = 0.296), as well as in the thoracic aorta, 7.7 m/W (5.25–9.90, P = 0.114), compared with healthy controls. There were no significant differences in wall shear stress parameters for all 5 regions of the thoracic aorta between the 3 groups. DAH patients, however, showed more vorticity, helicity and eccentricity in the ascending aorta compared with healthy controls (P < 0.019). CONCLUSIONS Decellularized long aortic homografts exhibit near to normal haemodynamic parameters 2.5 years postoperatively compared with healthy controls and VSARR.

Correction of heat-induced susceptibility changes in respiratory-triggered 2D-PRF-based thermometry for monitoring of magnetic resonance-guided hepatic microwave ablation in a human-like in vivo porcine model

Abstract: Abstract Purpose To develop and evaluate susceptibility corrected 2D proton resonance frequency (PRF)-based magnetic resonance (MR)-thermometry for the accurate assessment of the ablation zone of hepatic microwave ablation (MWA). Methods and materials Twelve hepatic MWA were performed in five LEWE minipigs with human-like fissure-free liver. Temperature maps during ablation of PRF-based MR-thermometry were corrected by modeling heat induced susceptibility changes. Ablation zones were determined using cumulative equivalent minutes at 43 °C (CEM43) as tissue damage model. T1 weighted (w) post-ablation contrast-enhanced (CE) MR-imaging and manually segmented postmortem histology were used for validation. The agreement of uncorrected (raw) and susceptibility corrected (corr) MR-thermometry with T1w post-ablation CE MR-imaging and histology was evaluated. The Wilcoxon-signed rank test and Bland–Altman analysis were applied. Results With the susceptibility corrected MR-thermometry a significantly increased dice coefficient (raw: 77% vs. corr: 83%, p < 0.01) and sensitivity (raw: 72% vs. corr: 82%, p < 0.01) was found for the comparison to T1w-CE imaging as well as histopathology (dice coefficients: raw: 76% vs. corr: 79%, p < 0.001; sensitivity: raw: 72% vs. corr: 74%, p < 0.001). While major axis length was significantly increased (7.1 mm, p < 0.001) and minor axis length significantly decreased (2.2 mm, p < 0.001) in uncorrected MR-thermometry compared to T1w-CE MR-imaging, no significant bias was found after susceptibility correction. Conclusion Using susceptibility corrected 2D PRF-based MR-thermometry to predict the ablation zones of hepatic MWA provided a good agreement in comparison to T1w post-ablation CE MR-imaging and histopathology.

Absolute thermometry using hyperpolarized 129Xe free‐induction decay and spin‐echo chemical‐shift imaging in rats

Abstract: To implement and test variants of chemical shift imaging (CSI) acquiring both free induction decays (FIDs) showing all dissolved‐phase compartments and spin echoes for specifically assessing 129$$ {}^{129} $$ Xe in lipids in order to perform precise lipid‐dissolved 129$$ {}^{129} $$ Xe MR thermometry in a rat model of general hypothermia.