Mukherji SK, consulting ed. Willinek WA, guest ed. Neuroradiology Applications of High-Field MR Imaging. Elsevier; May 2012. Neuroimaging Clinics of North America; vol. 22, no. 2, pgs. 123-402, $342.
The current issue of Neuroimaging Clinics of North America, Neuroradiology Applications of High Field MR Imaging, is edited by Dr. Winfried Willinek from Bonn, Germany. He has brought together 48 authors, who have authored 15 chapters dealing with the key issues in brain abnormalities (tumors, inflammation, neurodegenerative disease, epilepsy, stroke, vascular disease/imaging, head and neck imaging), spine abnormalities, topics dealing with pediatric CNS imaging, and potential future applications of even higher field strengths.
The definition of “high field MR” is a moving target. Not long ago, 1.5T was considered high field (perhaps now many consider it mid field), while, generally, 3T is considered high (or higher) field. That also is changing, given not only some of the information in this issue of the Neuroimaging Clinics of North America but also recent text books by Dr. Cho (7.O Tesla MR) and the detailed anatomic sections fixed brain specimens at 9.4 T as described by Dr. Naidich in Duvernoy’s Atlas of the Human Brain Stem and Cerebellum.
What is important in a volume like this is to describe and importantly to illustrate what 3T can accomplish compared to 1.5 T. This is particularly well demonstrated in the first chapter “Diffusion Tensor and Perfusion Imaging in Brain Tumors in High Field MR Imaging.” Here we see improved DTI at 3T vs. 1.5 when a high resolution matrix is used. Fiber tracking is also shown to be facilitated at the higher resolution compared to large matrix DTI at 3T. This comes as no surprise because of the increased signal and the higher resolution allowed, but it is good to see these side-by-side comparisons. Of course, we don’t have the benefit of seeing both 1.5 T and 3.0 T images on the same patient at the same time, but the inevitable conclusion is that 3T simply shows abnormalities better.
In inflammatory lesions of the brain (emphasis on MS), both non-contrast and contrast enhanced MR high field demonstrate smaller lesions better or show them when a 1.5 T image is negative. This chapter takes us beyond 3T and into what is termed ultrahigh field MR (>4T) to 7T. The 7T images in these selected MS cases are impressive, but one does wonder whether future neuroradiologists will view these 7T images without the awe they currently generate.
Most of the chapters demonstrate the pathology we commonly see at 1.5 T but just visualize it better at 3T. This is particularly so when one analyzes MRA images, both for the smaller penetrating vessels such as the lenticulostriate vessels and for the extent of visualization the midsized vessels. In the evaluation of epilepsy and some of the subtle findings causing seizures, 3T is shown to be dramatically superior. Examples include a small cavernoma, polomicrogyria, more precise hippocampal anatomy, hippocampal sclerosis, and other seizure-inducing lesions. This chapter is well illustrated and worth reviewing over and above the issue of high field.
That total evaluation of stroke and stroke parameters is improved by using 3T (or perhaps higher) is shown well in the chapter “Stroke: High Field Imaging,” whether it is by employing DCWI, ASL perfusion, or SWI. Again beyond the issue of high field, this chapter is worth a read just for the multifaceted areas of stroke analysis.
Of particular interest is the chapter by Marc Shapiro entitled “Imaging of the Spine at 3 Tesla.” While no one disputes the value of 3T in the brain, there has been some discontent with spine imaging at that field strength. Dr. Shapiro beautifully delineates the historical aspects of the introduction of spine 3T, the early problems encountered and their solutions, and the current technical aspects of 3T spine MR. What is particularly educational in the early portions of this chapter are the explanations of contrast enhancement improvement at 3T long with the improved signal. Readers may find the extensive tabular information for spine protocols interesting and useful as pertains routine imaging and in those patients with varying degrees of metal implantation. Examples chosen to show the important features of 3T spine imaging are good; one would have liked, however, to have had slightly larger and brighter images in a number of places. The use of advanced MR techniques, frequently brought with difficulties in the spine, are nicely dealt with (MRS, DWI, DTI permeability) and illustrated. The chapter includes multiple types of spine column and spinal cord lesions.
Since the economics of medical care is under such scrutiny these days, and since imaging seems to be in the cross hairs of diminished reimbursements, it would have been beneficial to have included a chapter on the economic realities of 3T and 7T systems, and to have compared these with 1.5 T systems, with all the costs purchase, cost maintenance, service contracts auxiliary costs such as coils/software shielding, room construction, included. While there may be no or little difference between 1.5 and 3T in some of these categories, there will be differences in other categories. Since reimbursement for these studies will not vary according to the magnet strength, one wonders whether the increased costs are justifiable. The other murky issue is whether in fact the better resolution and higher signal, both of which allow a more detailed look at the CNS, actually affects patient outcome. This is something many do not wish to acknowledge, but it is an on-rushing fact of medical imaging with which we must deal.
This is an issue of the Neuroimaging Clinics of North America that every neuroradiologist will be interested in, primarily because it helps define where 3T (and perhaps higher field strength) is going and what we can expect to derive from those images.
