Search

Background and purpose: Magnetic Resonance Imaging (MRI) is increasingly being used in radiotherapy (RT). However, geometric distortions are a known challenge of using MRI in RT. The aim of this study was to demonstrate feasibility of a national audit of MRI geometric distortions. This was achieved by assessing large field of view (FOV) MRI distortions on a number of scanners used clinically for RT. Materials and methods: MRI scans of a large FOV MRI geometric distortion phantom were acquired on 11 MRI scanners that are used clinically for RT in the UK. The mean and maximum distortions and variance between scanners were reported at different distances from the isocentre. Results: For a small FOV representing a brain (100–150 mm from isocentre) all distortions were 10 mm in some cases. The variance between scanners was low and was found to increase with distance from isocentre. Conclusions: This study demonstrated feasibility of the technique to be repeated in a country wide geometric distortion audit of all MRI scanners used clinically for RT. Recommendations were made for performing such an audit and how to derive acceptable limits of distortion in such an audit.

The Centre for Medical Image Computing (CMIC) at University College London (UCL) hosted a two-day workshop on placenta imaging on April 12th and 13th 2018. The workshop consisted of 10 invited talks, 3 contributed talks, a poster session, a public interaction session and a panel discussion about the future direction of placental imaging. With approximately 50 placental researchers in attendance, the workshop was a platform for engineers, clinicians and medical experts in the field to network and exchange ideas. Attendees had the chance to explore over 20 posters with subjects ranging from the movement of blood within the placenta to the efficient segmentation of fetal MRI using deep learning tools. UCL public engagement specialists also presented a poster, encouraging attendees to learn more about how to engage patients and the public with their research, creating spaces for mutual learning and dialogue.

We have used magnetic resonance imaging (MRI) to provide important new insights into the function of the human placenta in utero. We have measured slow net flow and high net oxygenation in the placenta in vivo, which are consistent with efficient delivery of oxygen from mother to fetus. Our experimental evidence substantiates previous hypotheses on the effects of spiral artery remodelling in utero and also indicates rapid venous drainage from the placenta, which is important because this outflow has been largely neglected in the past. Furthermore, beyond Braxton Hicks contractions, which involve the entire uterus, we have identified a new physiological phenomenon, the ‘utero-placental pump’, by which the placenta and underlying uterine wall contract independently of the rest of the uterus, expelling maternal blood from the intervillous space., MRI provides important new insights into the function of the human placenta, revealing slow net flow and high, uniform oxygenation in healthy pregnancies, detecting changes that will lead to compromised oxygen delivery to the fetus in preeclampsia, and identifying a new physiological phenomenon, the ‘utero-placental pump’.

Chemical Exchange Saturation Transfer (CEST) has been used to assess healthy and pathological tissue in both animals and humans. However, the CEST signal from blood has not been fully assessed. This paper presents the CEST and nuclear Overhauser enhancement (NOE) signals detected in human blood measured via z-spectrum analysis. We assessed the effects of blood oxygenation levels, haematocrit, cell structure and pH upon the z-spectrum in ex vivo human blood for different saturation powers at 7T. The data were analysed using Lorentzian difference (LD) model fitting and AREX (to compensate for changes in T1), which have been successfully used to study CEST effects in vivo. Full Bloch-McConnell fitting was also performed to provide an initial estimate of exchange rates and transverse relaxation rates of the various pools. CEST and NOE signals were observed at 3.5 ppm, −1.7 ppm and −3.5 ppm and were found to originate primarily from the red blood cells (RBCs), although the amide proton transfer (APT) CEST effect, and NOEs showed no dependence upon oxygenation levels. Upon lysing, the APT and NOE signals fell significantly. Different pH levels in blood resulted in changes in both the APT and NOE (at −3.5 ppm), which suggests that this NOE signal is in part an exchange relayed process. These results will be important for assessing in vivo z-spectra.

Purpose: To develop a method that fits a multipool model to z-spectra acquired from non–steady state sequences, taking into account the effects of variations in T1 or B1 amplitude and the results estimating the parameters for a four-pool model to describe the z-spectrum from the healthy brain. Methods: We compared measured spectra with a look-up table (LUT) of possible spectra and investigated the potential advantages of simultaneously considering spectra acquired at different saturation powers (coupled spectra) to provide sensitivity to a range of different physicochemical phenomena. Results: The LUT method provided reproducible results in healthy controls. The average values of the macromolecular pool sizes measured in white matter (WM) and gray matter (GM) of 10 healthy volunteers were 8.9%6 0.3% (intersubject standard deviation) and 4.4%6 0.4%, respectively, whereas the average nuclear Overhauser effect pool sizes in WM and GM were 5%6 0.1% and 3%6 0.1%, respectively, and average amide proton transfer pool sizes in WM and GM were 0.21%6 0.03% and 0.20%6 0.02%, respectively. Conclusions: The proposed method demonstrated increased robustness when compared with existing methods (such as Lorentzian fitting and asymmetry analysis) while yielding fully quantitative results. The method can be adjusted to measure other parameters relevant to the z-spectrum.

The conductivity and permittivity of biological tissue are critical to estimating local radiofrequency (RF) power deposition (also known as specific absorption rate SAR) for Ultra High Field Magnetic Resonance Imaging (UH-MRI). These electrical properties may also have diagnostic value as malignant tissue types have been shown to have higher permittivity and conductivity than surrounding healthy tissue [1]. Recently a new SAR calculation method of using the transmit B 1 + map to obtain tissue electrical property has been proposed as a fast SAR calculation method, and has demonstrated great potential for practical applications. However the current numerical technique used in the B 1 + map based electrical property calculation is based on a traditional Finite-Difference algorithm, and therefore it requires high-resolution original B 1 + map to achieve accurate electrical property calculation. In this study, we have proposed the Spline interpolation of low resolution MRI B 1 + map at 1.5T. The proposed method is robust in approximating complex shapes in medical images through curve fitting and therefore could provide sufficiently accurate approximation of the high resolution B 1 + map through the low resolution raw data. This will prove to be useful in the fast real time estimation of local specific absorption rate without compromising the accuracy of SAR calculation. It is found that the Spline interpolation method helps in the reduction of MRI scan time and fast estimation of the SAR

Pregabalin is a treatment option for patients with persistent neuropathic pain. Its use has been associated with changes in mood and the development of depression and/or suicidal ideation.Case presentations were reviewed of five patients reporting changes in mood, depression and suicidal ideation from the first 50 (approximately) patients commenced on pregabalin at the clinic.Although these patients had a history of depression, their mood had been stable before commencing pregabalin. Soon after commencement they reported changes in mood, and development of depression and/or suicidal ideation, which improved with dose reduction or cessation of pregabalin. Ultimately, all five patients ceased pregabalin treatment. Suicidal ideation is a recognised adverse effect of pregabalin. Patients should be warned of and monitored for deterioration in mood.