[Show abstract][Hide abstract]ABSTRACT: Aims:
People with Type 1 diabetes have smaller pancreases than healthy individuals. Several diseases causing pancreatic atrophy are associated with pancreatic steatosis, but pancreatic fat in Type 1 diabetes has not been measured. This cross-sectional study aimed to compare pancreas size and fat fraction in children with Type 1 diabetes and controls.
The volume and fat fraction of the pancreases of 22 children with Type 1 diabetes and 29 controls were determined using magnetic resonance imaging.
Pancreas volume was 27% smaller in children with diabetes (median 34.9 cm(3) ) than in controls (47.8 cm(3) ; P < 0.001). Pancreas volume correlated positively with age in controls (P = 0.033), but not in children with diabetes (P = 0.649). Pancreas volume did not correlate with diabetes duration, but it did correlate positively with units of insulin/kg body weight/day (P = 0.048). A linear model of pancreas volume as influenced by age, body surface area and insulin units/kg body weight/day found that insulin dosage correlated with pancreas volume after controlling for both age and body surface area (P = 0.009). Pancreatic fat fraction was not significantly different between the two groups (1.34% vs. 1.57%; P = 0.891).
Our findings do not indicate that pancreatic atrophy in Type 1 diabetes is associated with an increased pancreatic fat fraction, unlike some other diseases featuring reduced pancreatic volume. We speculate that our results may support the hypotheses that much of pancreatic atrophy in Type 1 diabetes occurs before the clinical onset of the disease and that exogenous insulin administration decelerates pancreatic atrophy after diabetes onset. This article is protected by copyright. All rights reserved.
Full-text available · Article · Mar 2016 · Diabetic Medicine
[Show abstract][Hide abstract]ABSTRACT: Purpose:
To study the feasibility and to gauge the potential clinical impact of quantifying small bowel motility using magnetic resonance imaging (MRI) in a larger population with a spectra of gastrointestinal conditions with impaired small bowel motility.
Materials and methods:
Data were gathered retrospectively from a cohort of 127 patients undergoing MR enterography (1.5 Tesla) in 2011. Cine motility sequences were processed with validated motility analysis software and a parametric motility map was generated. Regions of interests were drawn in the jejunum, ileum, and terminal ileum, and Jacobian standard deviation mean motility index' score (MIS) was calculated. Patients were divided into Crohn's disease (CD), ulcerative colitis, irritable bowel syndrome, and healthy subjects.
In CD, terminal ileum motility was lower in comparison to healthy subjects (mean difference: -0.1052 arbitrary units, 95% confidence interval: -0.1981--0.0122, P = 0.018). Subgrouping of CD showed that the difference was recognized in patients with disease limited to the small bowel (mean difference: -0.1440 arbitrary units, 95% confidence interval: -0.2491--0.0389, P = 0.002). Visible dysmotility of terminal ileum on MRI reflected a reduced MIS compared with normal motility (0.22 ± 0.09 and 0.33 ± 0.15 arbitrary units, respectively, P = 0.043). Motility correlated negatively between ileum and age (P = 0.021), and between terminal ileum and C-reactive protein in ulcerative colitis (P = 0.031).
Motility quantitation revealed a significant difference in motility of terminal ileum in patients with small bowel CD compared with healthy subjects, concording with visible dysmotility and inflammatory changes. J. Magn. Reson. Imaging 2016.
Article · Jan 2016 · Journal of Magnetic Resonance Imaging
[Show abstract][Hide abstract]ABSTRACT: Purpose
To investigate the precision, accuracy, and repeatability of water/fat imaging-based fat quantification in muscle tissue using a large flip angle (FA) and a fat reference for the calculation of the proton density fat fraction (FF). Comparison is made to a small FA water reference approach.
Materials and Methods
An Intralipid phantom and both forearms of six patients suffering from lymphedema and 10 healthy volunteers were investigated at 1.5T. Two multigradient-echo sequences with eight echo times and FAs of 10° and 85° were acquired. For healthy volunteers, the acquisition of the right arm was performed twice with repositioning. From each set, water reference FF and fat reference FF images were reconstructed and the average FF and the standard deviation were calculated within the subfascial compartment. The small FA water reference was considered the reference standard.
A high agreement was found between the small FA water reference and large FA fat reference methods (FF bias = 0.31%). In this study, the large FA fat reference approach also resulted in higher precision (38% smaller FF standard deviation in homogenous muscle tissue), but no significant difference in repeatability between the various methods was detected (coefficient of repeatability of small FA water reference approach 0.41%).
The precision of fat quantification in muscle tissue can be increased with maintained accuracy using a larger flip angle, if a fat reference instead of a water reference is used.
Full-text available · Article · Jun 2015 · Journal of Magnetic Resonance Imaging
[Show abstract][Hide abstract]ABSTRACT: In the first part of this chapter, methods for assessment of transendothelial permeability and perfusion by dynamic monitoring of an exogenous tracer, that is, dynamic contrast-enhanced magnetic resonance imaging (MRI) and dynamic susceptibility contrast MRI, are described, followed by an overview of arterial spin labeling techniques for quantification of cerebral blood flow using magnetically labeled arterial water as an endogenous tracer. The second part of the chapter deals with hyperpolarization techniques, allowing an increase in the MRI signal amplitude by several orders of magnitude in gaseous or liquid substances. Hyperpolarized agents and their applications are described, together with the associated MRI concepts and challenges.
[Show abstract][Hide abstract]ABSTRACT: To evaluate the distortion and artifact area of metal in MR images and to compare artifact reduction using different metal artifact-reducing sequences in patients with metal-on-metal (MoM) and non-MoM total hip prostheses.
Thirty-six MoM and 15 non-MoM prostheses were examined in a 1.5-T MR scanner using T1-weighted (T1-w) sequences: turbo spin echo (TSE) high-readout bandwidth (hiBW), T1-w; TSE view angle tilting (VAT), T1-w; TSE VAT + slice encoding for metal artifact correction (SEMAC); short tau inversion recovery (STIR) hiBW or matched RF pulses (mRFp). Distortion was quantified using a new method measuring the acetabular roof angle (ARA). The artifact area was defined in the mid-coronal plane of the artifact.
The T1 VAT + SEMAC sequence showed the least distortion compared to T1 VAT and T1-hiBW (150°, 127° and 102°, p < 0.001, in MoM; 152°, 143° and 128°, p ≤ 0.014, in non-MoM). The artifact area was smaller in MoM prostheses using the T1 VAT sequence compared to T1 hiBW and T1 VAT + SEMAC (2506 mm(2), 3160 mm(2) and 3214 mm(2), p < 0.001) and smaller in non-MoM prostheses using T1 VAT compared to T1-hiBW (4296 mm(2) and 4831 mm(2), p = 0.041). STIR-mRFp substantially reduced the artifact size compared with STIR-hiBW (MoM 4559 mm(2) and 6323 mm(2); non-MoM 5625 mm(2) and 8764 mm(2), p < 0.001).
Metal artifacts in MR imaging examinations of hip prostheses can be evaluated for distortion using a distortion angle (ARA) and the degree of signal artifact as determined by measuring the largest cross-sectional artifact area. T1 VAT + SEMAC showed the least distortion; T1 VAT and STIR-mRFp were most efficient for reduction of the artifact area.
[Show abstract][Hide abstract]ABSTRACT: Purpose:
To investigate various sources of bias in MRI-based quantification of fat fraction (FF) and fatty acid composition (FAC) using chemical shift-encoded techniques.
Signals from various FFs and FACs and individual relaxation rates of all signal components were simulated. From these signals, FF and FAC parameters were estimated with and without correction for differences in individual relaxation rates. In addition, phantom experiments were conducted with various flip angles and number of echoes to validate the simulations.
As expected, T(1) weighting resulted in an overestimation of the FF, but had much smaller impact on the FAC parameters. Differences in T(2) values of the signal components resulted in overestimation of the FAC parameters in fat/water mixtures, whereas the estimation in pure oil was largely unaffected. This bias was corrected using a simplified signal model with different T(2) values of water and fat, where the accuracy of the modeled T(2) of water was critical. The results of the phantom experiment were in agreement with simulations.
T(1) weighting has only a minor effect on FAC quantification in both fat/water mixtures and pure oils. T(2) weighting is mainly a concern in fat/water mixtures but may be corrected using a simplified model.
Article · Nov 2014 · Magnetic Resonance in Medicine
[Show abstract][Hide abstract]ABSTRACT: The current study was carried out to test the potential of a new nanomaterial (Spago Pix) as a macromolecular magnetic MR contrast agent for tumor detection and to verify the presence of nanomaterial in tumor tissue. Spago Pix, synthesized by Spago Nanomedical AB, is a nanomaterial with a globular shape, an average hydrodynamic diameter of 5 nm, and a relaxivity (r1) of approximately 30 (mM Mn)-1 s-1 (60 MHz). The material consists of an organophosphosilane hydrogel with strongly chelated manganese (II) ions and a covalently attached PEG surface layer. In vivo MRI of the MMTV-PyMT breast cancer model was performed on a 3 T clinical scanner. Tissues were thereafter analyzed for manganese and silicon content using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The presence of nanomaterial in tumor and muscle tissue was assessed using an anti-PEG monoclonal antibody. MR imaging of tumor-bearing mice (n = 7) showed a contrast enhancement factor of 1.8 (tumor versus muscle) at 30 minutes post-administration. Contrast was retained and further increased 2-4 hours after administration. ICP-AES and immunohistochemistry confirmed selective accumulation of nanomaterial in tumor tissue. A blood pharmacokinetics analysis showed that the concentration of Spago Pix gradually decreased over the first hour, which was in good agreement with the time frame in which the accumulation in tumor occurred. In summary, we demonstrate that Spago Pix selectively enhances MR tumor contrast in a clinically relevant animal model. Based on the generally higher vascular leakiness in malignant compared to benign tissue lesions, Spago Pix has the potential to significantly improve cancer diagnosis and characterization by MRI.
Full-text available · Article · Oct 2014 · PLoS ONE
[Show abstract][Hide abstract]ABSTRACT: Objective:
To apply and compare magnetic resonance imaging (MRI) metal artifact reducing sequences (MARS) including subtraction imaging after contrast application in patients with metal-on-metal (MoM) hip prostheses, investigate the prevalence and characteristics of periprosthetic abnormalities, as well as their relation with pain and risk factors.
Materials and methods:
Fifty-two MoM prostheses (35 cases with pain and or risk factors, and 17 controls) in 47 patients were examined in a 1.5-T MR scanner using MARS: turbo spin echo (TSE) with high readout bandwidth with and without view angle tilting (VAT), TSE with VAT and slice encoding for metal artifact correction (SEMAC), short tau inversion recovery (STIR) with matched RF pulses, and post-contrast imaging. The relations of MRI findings to pain and risk factors were analyzed and in five revised hips findings from operation, histology, and MRI were compared.
TSE VAT detected the highest number of osteolyses. Soft tissue mass, effusion, and capsular thickening were common, whereas osteolysis in acetabulum and femur were less frequent. Contrast enhancement occurred in bone, synovia, joint capsule, and the periphery of soft tissue mass. There was no significant relation between MRI findings and pain or risk factors.
MARS and gadolinium subtraction imaging are useful for evaluation of complications to MoM prosthesis. TSE VAT had the highest sensitivity for osteolysis. Contrast enhancement might indicate activation of aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL). Pain, small head, or steep prosthesis inclination angle are not useful predictors of periprosthetic abnormalities, and wide indications for MR follow-up are warranted.
[Show abstract][Hide abstract]ABSTRACT: Purpose To investigate the accuracy and noise performance of fat quantification with multiple gradient-echo images acquired using bipolar read-out gradients and compare them with those of the well-established unipolar technique. TheoryThe bipolar read-out technique induces phase and amplitude errors caused by gradient delays, eddy currents, and frequency-dependent coil sensitivity. In this study, these errors were corrected for jointly with the fat/water separation by modeling the impact of these effects on the signal. This approach did not require acquisition of reference data or modification of the pulse sequence. Methods
Simulations and a phantom experiment were used to investigate the accuracy and noise performance of the technique and compare them with those of a well-established technique using unipolar read-out gradients. Also, the in vivo feasibility was demonstrated for abdominal applications. ResultsThe phantom experiment demonstrated similar accuracy of the bipolar and unipolar fat quantification techniques. In addition, the noise performance was shown not to be affected by the added estimations of the phase and amplitude errors for most inter-echo times. Conclusion
The bipolar technique was found to provide accurate fat quantification with noise performance similar to the unipolar technique given an appropriate choice of inter-echo time. Magn Reson Med 71:219-229, 2014. (c) 2013 Wiley Periodicals, Inc.
Article · Jan 2014 · Magnetic Resonance in Medicine
[Show abstract][Hide abstract]ABSTRACT: To investigate the normal enhancement patterns of the scaphoid, lunate, and capitate bones with dynamic contrast-enhanced magnetic resonance imaging (MRI).
The study was approved by the hospital's Ethics Committee. Nineteen volunteers (13 female, 6 male; mean age 38 years) were examined and all gave written consent. Perfusion was assessed at 3 Tesla using dynamic contrast-enhanced MRI. After two-dimensional (2D) motion correction of the data set, regions of interest were placed in the capitate, lunate, and distal and proximal pole of scaphoid bone and from the mean signal intensities (SI), the enhancement was computed. The four locations were compared for time to peak, delay time, maximum enhancement, and maximum slope using Friedman's two-way analysis of variance.
Typical SI versus time curves revealed two components: a faster component with strong contrast enhancement and a slow component with prolonged enhancement. The mean value (standard deviation, SD) for maximum enhancement was 51 (33)% in the capitate, 54 (25)% in the lunate, 51 (34)% in the proximal pole and 51 (28)% in the distal pole of the scaphoid. The result of the Friedman test showed no significant difference (P < 0.05) in the perfusion variables between the capitate, lunate, and distal and proximal scaphoid bones.
Assessment of perfusion in normal carpal bone using contrast-enhanced MRI is possible. Optimization of the method and understanding of the normal perfusion may allow evaluation of pathological conditions such as osteonecrosis. J. Magn. Reson. Imaging 2013;38:168–172.
Article · Jul 2013 · Journal of Magnetic Resonance Imaging
[Show abstract][Hide abstract]ABSTRACT: PURPOSE
To investigate the perfusion of the carpal bones in normal volunteers and patients with suspicion of necrosis and determine whether there are different patterns in necrotic bone
METHOD AND MATERIALS
19 volunteers and 10 patients with avascular necrosis of the lunate or scaphoid carpal bone were examined on a 3-T scanner (Trio TIM, Siemens) with dynamic i.v. gadolinium contrast medium injection (0.1 mmol/kg, Dotarem, Guerbet). The slice position was determined using scout images in 3 planes to ensure accurate selection of medullary bone. Three sagittal image sections were placed in a folding fan-like arrangement. 23 consecutive T1-w GRE FS images, each with duration of 20 s, were acquired, resulting in a total acquisition time of 6 min and 40 s. Gd-injection was started at the end of the first image acquisition. The increase in signal intensity over time was measured in different ROIs placed over the distal and proximal poles of the scaphoid, lunate, capitate bones or fragments. A gamma-variate function were fitted to the data and the maximum enhancement, maximum slope were calculated. The ROIs were compared using Friedman´s two way analysis of variance and Wilcoxon Signed Rank tests.
Generally, vascularisation of the carpal bones could be measured. SI versus time curves delineated a faster component with strong and a slow component with prolonged enhancement. In normal volunteers there was no significant difference between the carpal bones in maximum enhancement and slope values. The bones (lunate = 8, scaphoid = 2) or fragments of 10 patients with avascular necrosis showed significantly higher values of maximum enhancement and steeper slope compared to normal carpals.
Dynamic gadolinium-enhanced MRI is able to assess perfusion in normal carpal bones and demonstrate different vascularity compared to necrotic bones.
The vascular supply of the scaphoid, lunate and capitate bones has unique patterns, placing them at risk for osteonecrosis. Early detection of altered perfusion may allow a more favorable treatment.
[Show abstract][Hide abstract]ABSTRACT: Magnetic resonance spectroscopy (MRS) has long been considered the golden standard for non-invasive measurement of tissue fat content. With improved techniques for fat/water separation, imaging has become an alternative to MRS for fat quantification. Several imaging models have been proposed, but their performance relative to MRS at very low fat contents is yet not fully established. In this work, imaging and spectroscopy were compared at 1.5 T and 3 T in phantoms with 0-3% fat fraction (FF). We propose a multispectral model with individual a priori R(2) relaxation rates for water and fat, and a common unknown R(2)' relaxation. Magnitude and complex image reconstructions were also compared. Best accuracy was obtained with the imaging method at 1.5 T. At 3 T, the FFs were underestimated due to larger fat-water phase shifts. Agreement between measured and true FF was excellent for the imaging method at 1.5 T (imaging: FF(meas)=0.98 FF(true)-0.01%, spectroscopy: FF(meas)=0.77 FF(true)+0.08%), and fair at 3 T (imaging: FF(meas)=0.91 FF(true)-0.19%, spectroscopy: FF(meas)=0.79 FF(true)+0.02%). The imaging method was able to quantify FFs down to approx. 0.5%. We conclude that the suggested imaging model is capable of fat quantification with accuracy and precision similar to or better than spectroscopy and offers an improvement vs. a model with a common R(2)* relaxation only.
[Show abstract][Hide abstract]ABSTRACT: PURPOSE
The purpose of the present study was to compare MRI pulse sequences with different techniques for artifact suppression. Three hip prostheses made of different materials were imaged and the artifacts were quantified with respect to both slice bending and in-plane artifact size.
METHOD AND MATERIALS
Three hip prostheses (A: BHR Cobalt-Chromium, B: Stryker Exeter stainless steel, C: Stryker Omnifit Titanium + Co-Cr) were embedded into agarose gel together with a rectilinear Perspex grid. The true extent of the prostheses were determined by X-ray projections. MR images aligned with the grid were acquired on an 1.5-T scanner (Siemens Avanto, equipped with new pulse sequences for implant imaging (WARP package)). Three types of MRI pulse sequences were evaluated: TSE: a standard turbo spin echo (BW 751 Hz/px), VAT: a turbo spin echo with view-angle tilting (BW 977 Hz/px), SEMAC: a turbo spin echo with both VAT and slice distortion correction (BW 977 Hz/px). All sequences had a voxel size of 0.74 x 0.74 x 3 mm3. The slice bending artifacts were quantified by adding together the length of the visible gridlines of the central slice and dividing by the true length. The in-plane artifacts were quantified by dividing the artifact area with the true prosthesis area. For both scores, 100% represents an artifact-free image.
For both the TSE and the VAT sequences, the slice bending artifact score was 80% for the Co-Cr prosthesis (A), 81% for the steel prosthesis (B) and 94% for the Ti prosthesis (C). The SEMAC sequence with 16 encoding steps achieved 96% (A and B), and 98% (C). The score for the in-plane artifact area was for the TSE-sequence 189% (A), 167% (B),117% (C). The VAT-sequence scored 172% (A), 143% (B), 108% (C). The SEMAC sequence with 16 encoding steps scored 106% (A), 110% (B), 101% (C).
The VAT sequence reduces in-plane artifacts compared to an optimized TSE sequence, but does not address artifacts from a distorted slice profile. The SEMAC sequence significantly reduces both types of artifacts, at the price of a much prolonged scan time. The titanium prosthesis produced much smaller artifacts than the Co-Cr prostheses and could be almost perfectly reproduced using the SEMAC sequence.
A combination of the VAT and SEMAC techniques allows visualization of tissues near, or directly at, the surface of metal prostheses, and can therefore reveal pathology not accessible by CT or X-ray.
[Show abstract][Hide abstract]ABSTRACT: PURPOSE
To evaluate issues involved with DWI of the liver at 3-T and to determine whether there might be any potential benefit for imaging at 3-T compared with 1.5-T
METHOD AND MATERIALS
Three DWI sequences using 9 b-values from 0-400 s/mm2 were designed with identical parameters on 3-T & 1.5-T (Siemens Medical Solutions) but with different strategies for handling of respiratory motion [respiratory triggered (RT), free breathing (FB), breath hold (BH)]. To verify accuracy of ADC quantification a phantom with different sucrose solution concentrations was constructed. Thirteen healthy volunteers were examined. DW images were analyzed quantitatively and qualitatively. ROIs were placed in the cranial, middle and caudal part of the right liver lobe (RLL) and ADC and SNR calculated. DWI of each sequence were qualitatively analyzed including motion/pulsation artifacts, distortion, magnetic susceptibility, chemical shift & ghosting and graded using a 4-point scale. Paired t tests were used to compare SNR and ADC values, Wilcoxon signed rank test to compare the qualitative ratings.
Nearly identical ADC values were obtained in the phantom experiments for all sequences and both magnetic field strengths. In vivo, the ADCs tended generally to be lower at 3-T than at 1.5-T. Most reproducible were ADC measurements with RT both at 3-T & 1.5-T, but best at 3-T in the middle RLL. The highest ADCs were found caudally in RLL, both at 3-T & 1.5-T. Significant differences in ADC between middle and caudal part of RLL were calculated in FB and RT at 3-T and FB and BH at 1.5-T, respectively. No significant difference in SNR was found between 3-T & 1.5-T and the three sequences. There were significantly more artifacts in left liver lobe (LLL) compared to RLL in all sequences at both 3-T & 1.5-T and significantly more artifacts in LLL at 3-T compared to 1.5-T.
Our preliminary study indicates that 3-T can provide DWI of the liver that may be superior to DWI acquired at 1.5-T, particularly when a respiratory-triggered or free-breathing sequence approach are chosen and ADCs are measured in the middle of RLL.
Assessment and follow-up of diffuse liver disease using ADC should be performed in the middle of the right liver lobe because of best reproducibility/least variation and preferably at 3-T.