MRI Methods Development

Our clinical system is a Siemens Tim Trio, which comprises an actively shielded 3T magnet, single transmit channel, and a 32 channel receiver system. The magnet is relatively short and wide bore (2m long with 60mm bore size) and designed to avoid claustrophobia. We’re currently running syngoMR software VB15 and have a range of RF coils including a CP integrated body coil (used mainly to transmit) and the following receiver coils: a 12 channel head array, a 32 channel head array, a neck array, spine array, flex coils etc. According to the specs, we have a gradient set that provides maximum amplitude of 40mT/m and maximum slew rate of 200mT/m/s, but I wouldn’t believe everything you read. Several members of the group are officially trained-up IDEA programmers, which gives us the flexibility to modify and develop pulse sequences to suit particular applications. A couple of us even went on the ICE course, but we don’t like to talk about that.

Development of arterial spin labelling MRI methods for mapping cerebral perfusion in the human brain.

David Thomas, Roger Ordidge, Aaron Oliver-Taylor.

Arterial spin labelling is a completely non-invasive MRI method for imaging cerebral blood flow. It uses RF pulses to magnetically label arterial blood water as it flows towards the brain, and this labelled water then acts as an endogenous tracer for the assessment of cerebral perfusion. The aims of this study are to implement current ASL methods on the 3T TRIO and to evaluate their relative performance and to develop new methods for ASL MRI, specifically:

  • Use a highly efficient single shot 3D acquisition method (GRASE), which will enable good volume coverage and SNR
  • Develop an additional neck RF coil specifically for performing the spin labelling, offering the benefits of straightforward volume imaging, reduced power deposition, and arterial territory mapping.
Human Cerebral Perfusion Images at 3T

MR safety related to imaging implants.

David Carmichael, Roger Ordidge, Louis Lemieux.

Imaging patients with conductive implants is an important area of research both because of their increased usage and due to the importance of MRI for clinical and research purposes. However, scanning patients with these implants can be a safety risk. In recent years, we have examined the safety of a number of these implants on a number of scanners including the TRIO. Initially, we investigated deep brain stimulator safety during fMRI. Following this, we have worked on the safety of imaging patients with intracranial EEG electrodes for localisation purposes, while more recently this was extended to performing intracranial EEG correlated fMRI in terms of both tissue heating and gradient induced voltages. Work currently ongoing involves optimising imaging protocols both structural and functional because image quality is degraded proximal to the implants.

Simulated electromagnetic interaction of implanted electrodes

Image from

Carmichael, D.W., Hand, J., Li, Y., McEvoy, A., Lemieux, L., 2008b. Estimating Specific Absorption Rate (SAR) during MRI in the human brain with intracranial EEG electrodes used for epilepsy monitoring: a preliminary study using finite integral technique (FIT) modelling. Proc. International Meeting of the ISMRM1061 (Toronto).

Related Publications

Carmichael,D.W., Thornton,J.S., Rodionov,R., Thornton,R., McEvoy,A.W., Ordidge,R.J., Allen,P.J., Lemieux,L. (2010). Feasibility of simultaneous intracranial EEG-fMRI in humans: a safety study. Neuroimage. 49(1), 379-390.

Carmichael,D.W., Thornton,J.S., Rodionov,R., Thornton,R., McEvoy,A., Allen,P.J., Lemieux,L. (2008). Safety of localizing epilepsy monitoring intracranial electroencephalograph electrodes using MRI: radiofrequency-induced heating. Journal of Magnetic Resonance Imaging 28(5), 1233-1244. ISSN: 1053-1807.

Carmichael,D.W., Pinto,S., Limousin-Dowsey,P., Thobois,S., Allen,P.J., Lemieux,L., Hariz,M., Yousry,T., Thornton,J.S. (2007). Functional MRI with active, fully implanted, deep brain stimulation systems: safety and experimental confounds. Neuroimage 15(2), 508-517.

Spatial Localisation Technique Development

The group has developed several important improvements to spatial localisation techniques for MR spectroscopy.  Most notably, the introduction of wide-bandwidth (FOCI - shaped) adiabatic radio-frequency pulses have led to substantial improvements in the accuracy of localisation, the minimisation of spectral distortion and also lead to the improvement of other techniques such as cerebral blood flow measurements.

Structural Imaging Development

David Thomas, David Carmichael, Roger Ordidge

Over recent years we have been making improvements to structural imaging sequences. T1-weighted scans such as MDEFT have been optimised for contrast and spatial uniformity. We have also developed improved T2-weighted FSE sequences by optimising the quality using methods from parallel imaging. The use of a 32-channel head coil on the TRIO system builds on our previous work developing array coils for improved structural imaging.

FSEimage

Related Publications

Carmichael,D.W., Thomas,D.L., Ordidge,R.J. (2009). Reducing ghosting due to k-space discontinuities in fast spin echo (FSE) imaging by a new combination of k-space ordering and parallel imaging. Journal of Magnetic Resonance 200(1), 119-125. ISSN: 1090-7807.

Carmichael,D.W., Thomas,D.L., De Vita,E., Fernandez-Seara,M.A., Chhina,N., Cooper,M., Sunderland,C., Randell,C., Turner,R., Ordidge,R.J. (2006). Improving whole brain structural MRI at 4.7 Tesla using 4 irregularly shaped receiver coils. NeuroImage 32(3), 1176-1184. ISSN: 1053-8119.

3D MDEFT imaging of the human brain at 4.7 T with reduced sensitivity to radiofrequency inhomogeneity. Thomas DL, De Vita E, Deichmann R, Turner R, Ordidge RJ. Magn Reson Med. 2005 Jun;53(6):1452-8.