Pancreatic adipose tissue infiltration, parenchymal steatosis and beta cell function in humans.

AIMS/HYPOTHESIS: This study aimed to perform a comprehensive analysis of interlobular, intralobular and parenchymal pancreatic fat in order to assess their respective effects on beta cell function. METHODS: Fifty-six participants (normal glucose tolerance [NGT] (n = 28), impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) (n = 14) and patients with type 2 diabetes (n = 14)) underwent a frequent-sampling OGTT and non-invasive magnetic resonance imaging (MRI; whole-body and pancreatic) and proton magnetic resonance spectroscopy ((1)H-MRS; liver and pancreatic fat). Total pancreatic fat was assessed by a standard 2 cm(3) (1)H-MRS method, intralobular fat by 1 cm(3) (1)H-MRS that avoided interlobular fat within modified DIXON (mDIXON) water images, and parenchymal fat by a validated mDIXON-MRI fat-fraction method. RESULTS: Comparison of (1)H-MRS techniques revealed an inhomogeneous distribution of interlobular and intralobular adipose tissue, which increased with decreasing glucose tolerance. mDIXON-MRI measurements provided evidence against uniform steatosis, revealing regions of parenchymal tissue void of lipid accumulation in all participants. Total (r = 0.385, p < 0.01) and intralobular pancreas adipose tissue infiltration (r = 0.310, p < 0.05) positively associated with age, but not with fasting or 2 h glucose levels, BMI or visceral fat content (all p > 0.5). Furthermore, no associations were found between total and intralobular pancreatic adipose tissue infiltration and insulin secretion or beta cell function within NGT, IFG/IGT or patients with type 2 diabetes (all p > 0.2). CONCLUSIONS/INTERPRETATION: The pancreas does not appear to be another target organ for abnormal endocrine function because of ectopic parenchymal fat storage. No relationship was found between pancreatic adipose tissue infiltration and beta cell function, regardless of glucose tolerance status.

Initial clinical application of modified Dixon with flexible echo times: hepatic and pancreatic fat assessments in comparison with (1)H MRS.

OBJECTS: Hepatic and pancreatic fat content become increasingly important for phenotyping of individuals with metabolic diseases. This study aimed to (1) evaluate hepatic fat fractions (HFF) and pancreatic fat fractions (PFF) using (1)H magnetic resonance spectroscopy (MRS) and the recently introduced fast mDixon method, and to examine body fat effects on HFF and PFF, (2) investigate regional differences in HFF and PFF by mDixon. MATERIALS AND METHODS: HFF and PFF were quantified by mDixon with two flexible echo times and by single voxel (1)H MRS in 24 healthy subjects. The regional differences of PFF within the pancreas were assessed with mDixon. Abdominal visceral and subcutaneous fat was assessed by T1-weighted MRI at 3T. RESULTS: Both methods correlated well for quantification of HFF (r = 0.98, p < 0.0001) and PFF (r = 0.80, p < 0.0001). However, mDixon showed a higher low limit in HFF and PFF. PFF showed no regional differences using mDixon. In addition, both visceral and subcutaneous fat correlated with pancreatic fat, while only visceral fat correlated with liver fat, employing both (1)H MRS and mDixon. CONCLUSION: The novel and fast two-point mDixon exhibits a good correlation with the gold-standard (1)H MRS for assessment of HFF and PFF, with limited sensitivity for assessing lower fat content.

Quantitative liver 31P magnetic resonance spectroscopy at 3T on a clinical scanner.

PURPOSE: The aims of this study were (i) to establish a robust and fast method to quantify hepatocellular phosphorus compounds in molar concentration on a 3T clinical scanner, (ii) to evaluate its reproducibility, and (iii) to test its feasibility for a use in large cohort studies. METHOD: Proton-decoupled (31) P magnetic resonance spectroscopy of liver (31) P compounds were acquired on 85 healthy subjects employing image selected in-vivo spectroscopy localization in 13 min of acquisition at 3T. Absolute quantification was achieved using an external reference and double-matching phantoms (inorganic phosphates and adenosine triphosphate (ATP) solutions). Reproducibility of the method was also examined. RESULTS: This method showed a high intra- and interday as well as inter- and intraobserver reproducibility (r > 0.98; P < 0.001), with a high signal to noise ratio (SNR) (i.e., mean SNR of γ-ATP: 16). The mean liver concentrations of 85 healthy subjects were assessed to be 1.99 ± 0.51 and 2.74 ± 0.55 mmol/l of wet tissue volume for Pi and γ-ATP, respectively. CONCLUSION: This method reliably quantified molar concentrations of liver (31) P compounds on 85 subjects with a short total examination time (∼25 min) on a 3T clinical scanner. Thus, the current method can be readily utilized for a clinical study, such as a large cohort study.

Percutaneous abscess drainage using near real-time MR guidance in an open 1.0-T MR scanner: proof of concept.

OBJECTIVES: The aims of our study were (1) to assess the feasibility, effectiveness, and safety of exclusively magnetic resonance (MR)-guided freehand percutaneous abscesses drainage using a 1.0-T open MR scanner and (2) to evaluate the optimal method to visualize drainage catheters in situ. MATERIAL AND METHODS: In vitro studies in a dedicated MR gelatin phantom were performed to assess visualization of 8 different sizes of drainage catheters after instillation of sole 0.9% sodium chloride (NaCl) and diluted (1.0%) or concentrated (12.0%) gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) using a T1-weighted (T1w) 2-dimensional fast field echo (FFE) and a T2-weighted single-shot (ssh) turbo spin-echo (TSE) fast dynamic sequence. The catheter artifacts were evaluated with regard to the contrast-to-noise ratio (CNR), the artifact width using the full width at half-maximum (FWHM) method, and the artifact intensity, being the product of the CNR and the FWHM. We used the general linear model procedure as the global test and the Tukey studentized range test for post hoc analysis. In vivo MR-guided freehand drainage was prospectively performed in patients with increased systemic inflammation markers and abdominal, retroperitoneal, and pelvic abscess collections. This study had been approved by the institutional review board. All patients provided written informed consent. Technical success was the primary efficacy variable. The secondary efficacy variables were visibility of the puncture needle and drainage catheter artifact, using a qualitative 5-point rating scale, intervention and procedure time, and rate of postinterventional complications. RESULTS: The FWHM, the CNR, and the artifact intensity of the drainage catheters filled with 0.9% NaCl or diluted or concentrated Gd-DTPA increased according to the drainage catheter size in an almost linear fashion in both image weighting (all P ≤ 0.006; all R(2) ≥ 0.73). The T1w FFE sequence yielded the highest FWHM, CNR, and artifact intensity of all groups, using 12.0% Gd-DTPA instillation (all P < 0.001), and the least FWHM and artifact intensity, using 1.0% Gd-DTPA instillation (all P < 0.022; all P < 0.009). The T2w ssh TSE yielded higher FWHM, using 12.0% Gd-DTPA instillation, whereas the CNR was higher for 0.9% NaCl instillation (all P < 0.001). Magnetic-resonance-guided abscess drainage was performed in 22 patients with 24 abdominal, retroperitoneal, or pelvic abscess collections. The technical success rate of in vivo MR-guided freehand drainage was 100%. Visibility of the puncture needle was excellent (≥4.4 [0.5] points). Visibility of the drainage catheters was rated with 3.9 (0.9) and 4.5 (0.8) points using T2w ssh TSE with 0.9% NaCl and 12.0% Gd-DTPA instillation as well as 4.8 (0.5) and 4.2 (0.8) points using T1w FFE with 1.0% and 12.0% Gd-DTPA instillation, respectively. The procedure and intervention time was 52.4 (16.4) minutes (range, 28-78 minutes) and 27.4 (7.2) minutes (range, 17-40 minutes). Two minor and no major complications were recorded. CONCLUSIONS: Magnetic-resonance-guided freehand percutaneous abscesses drainage using fast dynamic sequences in an open 1-T MR scanner is feasible, effective, and safe. Visualization of drainage catheters can be facilitated by instillation of 0.9% NaCl or diluted or concentrated contrast media.

MR-guided freehand biopsy of liver lesions with fast continuous imaging using a 1.0-T open MRI scanner: experience in 50 patients.

The purpose of this study was to assess a new open system with a field-strength of 1.0 T for the feasibility of liver biopsy using the freehand technique with fast continuous imaging. Fifty patients with focal liver lesions measuring 5 to 30 mm in diameter were included in the study. Guidance and monitoring was performed using a 1.0-T open magnetic resonance (MR) scanner (Panorama HFO; Philips Healthcare, Best, The Netherlands). With fast continuous imaging using a T1-weighted (T1W) gradient echo (GRE) sequence after administration of gadolinium (Gd)-EOB-DTPA, the needle was placed into the lesion. An interface for interactive dynamic viewing in two perpendicular planes prevented needle deviations T2-weighted turbo spin echo (TSE) fat-suppressed sequence was added to rule out postinterventional hematoma or biloma. All lesions were visible on the interventional images. Biopsy was technically successful, and solid specimens were obtained in all cases. Forty-six patients showed a histopathologic pattern other than native liver tissue, thus confirming correct position of the needle. Time between determination of the lesion and performance of the control scan was on average 18 min. No major complications were recorded. MR guidance with the new 1-T open system must be considered an attractive alternative for liver punction. An interface for dynamic imaging of needle guidance and T1W-GRE imaging with administration of Gd-EOB-DTPA for contrast enhancement allows the pinpoint puncture of liver lesions.

MR imaging guided percutaneous nephrostomy using a 1.0 Tesla open MR scanner.

PURPOSE: The purpose of this study was to assess the safety and feasibility of MR-guided percutaneous nephrostomy (PCN) using a 1.0 Tesla open MR-scanner with fast dynamic imaging. METHODS: Twenty-five patients with failed ultrasonographic insertion due to various reasons, such as nondilated pelvic systems, obesity, and parapelvic cysts, were investigated. RESULTS: In summary, 35 nephrostomy procedures were performed; 15 patients received monolateral and 10 patients bilateral placement. For guidance and monitoring, fast T2w single-shot-TSE imaging in a fluoroscopic mode in two orthogonal planes was used to guide the insertion of the needle into a predetermined calyx in freehand technique. Nephrostomy was inserted via Seldinger-technique. The procedure was regarded as technically successful if the placement of the catheter provided adequate drainage of the collecting system. Demonstration of an intrapelvic position of the catheter was verified by antegrade pyelography using T1w GRE imaging after injection of diluted Gd-DTPA into the collecting system. Under the experimental conditions of the study, the time for the complete procedure was 30 (range, 23-39) min. Puncture and placement of the nephrostomy was performed in 5 (range, 3-10) min on average. CONCLUSIONS: Our results demonstrated a pinpoint puncture of the pelvic system in a reasonable timeframe even in patients with difficult conditions, suggesting that MR-guided PCN using the open 1 Tesla system can be assessed as a reliable, fast, and safe method applicable in the clinical routine setting.

MR-guided liver tumor ablation employing open high-field 1.0T MRI for image-guided brachytherapy.

OBJECTIVE: To determine the feasibility and safety of image-guided brachytherapy employing a modified open high-field MR system. METHODS: This is a follow-up study of a development project enabling technologies for interventional use of 1.0T open MRI. Modifications included coils and in-bore visualization, fluoroscopic sequences and user interfaces. We recruited 104 patients with 224 liver malignancies to receive MR-guided brachytherapy. Interventions were performed >20 min after Gd-EOB-DTPA. We recorded interventional parameters including the intervention time (from acquisition of the first scout until the final sequence for brachytherapy treatment planning). Two reviewers assessed MR-fluoroscopic images in comparison to plain CT as used in CT intervention, applying a rating scale of 1-10. Statistical analysis included Friedman and Kendall's W tests. RESULTS: We employed freehand puncture with interactive dynamic imaging for navigation. Technical success rate was 218 complete ablations in 224 tumours (97%). The median intervention time was 61 min. We recorded no adverse events related to the use of MRI. No major complications occurred. The rate of minor complications was 4%. Local control at 3 months was 96%. Superiority of MR-fluoroscopic, Gd-EOB-DTPA-enhanced images over plain CT was highly significant (P < 0.001). CONCLUSION: MR-guided brachytherapy employing open high-field MRI is feasible and safe.

Spectroscopic imaging: basic principles.

Spectroscopic imaging (SI) is a method that enables the measurement of the spatial distribution of metabolite concentrations in tissue. In this paper, an overview of measurement and processing techniques for SI is given. First, the basic structure of SI pulse sequences is introduced and the concepts of k-space, point spread function and spatial resolution are described. Then, special techniques are presented for the purpose of eliminating spurious signals and reducing measurement time. Finally, basic post-processing of SI data and the methods for viewing the results of SI measurement are summarized.

Intraoperative functional MRI as a new approach to monitor deep brain stimulation in Parkinson's disease.

This article deals with technical aspects of intraoperative functional magnetic resonance imaging (fMRI) for monitoring the effect of deep brain stimulation (DBS) in a patient with Parkinson's disease. Under motor activation, therapeutic high-frequency stimulation of the subthalamic nucleus was accompanied by an activation decrease in the contralateral primary sensorimotor cortex and the ipsilateral cerebellum. Furthermore, an activation increase in the contralateral basal ganglia and insula region were detected. These findings demonstrate that fMRI constitutes a promising clinical application for investigating brain activity changes induced by DBS.

Functional MRI using sensitivity-encoded echo planar imaging (SENSE-EPI).

Parallel imaging methods become increasingly available on clinical MR scanners. To investigate the potential of sensitivity-encoded single-shot EPI (SENSE-EPI) for functional MRI, five imaging protocols at different SENSE reduction factors (R) and matrix sizes were compared with respect to their noise characteristics and their sensitivity toward functional activation in a motor task examination. At constant echo times, SENSE-EPI was either used to shorten the single volume acquisition times (TR(min)) at matrix size 128 x 100 (22 slices) from 3.9 s (no SENSE) to 2.0 s at R = 3, or to increase the matrix size to 192 x 153 (22 slices), resulting in TR(min) = 5.3 s for R = 2 or TR(min) = 3.4 s for R = 3. At the lower resolution, the bisection of echo train length (R = 2) substantially reduced distortions and blurring, while signal-to-noise and statistical power (measured by cluster size and maximum t value per unit time) were hardly reduced. At R = 3 the additional gain in speed and distortion reduction was quite small, while signal-to-noise and statistical power dropped significantly. With enhanced spatial resolution the time course signal-to-noise was better than expected from theory for purely thermal noise because of a reduced contribution of physiological noise, and statistical power almost reached that of the regular, low-resolution single-shot EPI, with a slight drop off toward R = 3. Thus, SENSE-EPI allows to substantially increase speed and spatial resolution in fMRI. At SENSE reduction factors up to R = 2, the potential drawbacks regarding signal-to-noise and statistical power are almost negligible.