Johannes M. Peeters

Origin and reduction of motion and f0 artifacts in high resolution T2*-weighted magnetic resonance imaging: application in Alzheimer's disease patients.

The altered iron concentration in many neurodegenerative diseases such as Alzheimers disease (AD) has led to the development of MRI sequences that are sensitive to the accompanying changes in the transverse relaxation rate. Heavily T(2)*-weighted imaging sequences at high magnetic field strength (7T and above), in particular, show potential for detecting small changes in iron concentration. However, these sequences require a long echo time in combination with a long scanning time for high resolution and are therefore prone to image artifacts caused by physiological fluctuations, patient motion or system instabilities. Many groups have found that the high image quality that was obtained using high resolution T(2)*-weighted sequences at 7T in healthy volunteers, could not be obtained in AD patients. In this study the source of the image artifacts was investigated in phantom and in healthy volunteer experiments by incorporating movement parameters and resonance frequency (f0) variations which were measured in AD patients. It was found that image degradation caused by typical f0 variations was a factor-of-four times larger than artifacts caused by movement characteristic of AD patients in the scanner. In addition to respiratory induced f0 variations, large jumps in the f0 were observed in AD patients. By implementing a navigator echo technique to correct for f0 variations, the image quality of high resolution T(2)*-weighted images increased considerably. This technique was successfully applied in five AD patients and in five subjective memory complainers. Visual scoring showed improvements in image quality in 9 out of 10 subjects. Ghosting levels were reduced by 24+/-13%.

SENSE with improved tolerance to inaccuracies in coil sensitivity maps

In this work, an extension of the Cartesian sensitivity encoding (SENSE) parallel imaging framework is proposed. In the well‐known SENSE solution, the overdetermined reconstruction inversion problem is optimized to get the highest signal‐to‐noise ratio in the image. In this extension, the probability of artifacts due to incorrect knowledge of the receiver coil sensitivities is also taken into account. This is realized by assuming an uncertainty in measured receiver coil sensitivities to enable weighting of residual artifact level and signal‐to‐noise ratio in the inversion problem. This inversion problem can still be solved by a least‐squares optimization without the need of any complex iterative scheme. Results in abdominal imaging show that artifact levels can be substantially reduced, at the cost of a signal‐to‐noise ratio penalty. The size of the signal‐to‐noise ratio penalty depends on the assumed inaccuracy of the coil sensitivities, sensitivity encoding acceleration factor, and coil configuration. Magn Reson Med, 2013.

Passive radiofrequency shimming in the thighs at 3 Tesla using high permittivity materials and body coil receive uniformity correction.

To explore the effects of high permittivity dielectric pads on the transmit and receive characteristics of a 3 Tesla body coil centered at the thighs, and their implications on image uniformity in receive array applications.

Performance of a fast and high‐resolution multi‐echo spin‐echo sequence for prostate T2 mapping across multiple systems

To evaluate the performance of a multi‐echo spin‐echo sequence with k‐t undersampling scheme (k‐t T2) in prostate cancer.

GRASE Revisited: breath-hold three-dimensional (3D) magnetic resonance cholangiopancreatography using a Gradient and Spin Echo (GRASE) technique at 3T

ObjectiveTo evaluate the clinical feasibility and image quality of breath-hold (BH) three-dimensional (3D) magnetic resonance cholangiopancreatography (MRCP) using a gradient and spin-echo (GRASE) technique compared to the conventional 3D respiratory-triggered (RT)-MRCP using a turbo spin-echo (TSE) sequence at 3 T.MethodsSixty-six patients underwent both 3D RT-TSE-MRCP and 3D BH-GRASE-MRCP at 3 T. Three radiologists independently reviewed the visualisation of biliary and pancreatic ducts, image blurring, and overall image quality of the two data sets using four- or five-point scales. The numbers of scans with non-diagnostic or poor image quality were compared between the two scans.ResultsThe 3D BH-GRASE-MRCP had a significantly better image quality (3.69 ± 0.77 vs. 3.30 ± 1.18, p = 0.005) and less image blurring (3.23 ± 0.94 vs. 3.65 ± 0.57, p = 0.0003) than the 3D RT-TSE-MRCP. In detail, 3D BH-GRASE-MRCP better depicted the common bile duct, cystic duct, and bilateral first intrahepatic duct (all ps < 0.05). The number of scans with non-diagnostic or poor image quality significantly decreased with 3D BH-GRASE-MRCP compared with 3D RT-TSE-MRCP [19.7% (13/66) vs. 1.5% (1/66), p = 0.002].ConclusionThe 3D BH-GRASE-MRCP provided better image quality and a reduced number of non-diagnostic images compared to 3D RT-TSE-MRCP.Key points• The GRASE technique enabled 3D MRCP acquisition within a single breath-hold.• The short acquisition time of 3D BH-GRASE-MRCP significantly reduced image blurring.• The 3D BH-GRASE-MRCP had a better image quality than 3D RT-TSE-MRCP.• The number of non-diagnostic scans was reduced with 3D BH-GRASE-MRCP.