Imaging the adult brain

Evaluation of epidural and peripheral nerve catheter heating during magnetic resonance imaging

BACKGROUND

Many epidural and peripheral nerve catheters contain conducting wire that could heat during magnetic resonance imaging (MRI), requiring removal for scanning.

METHODS

We tested 2 each of 6 brands of regional analgesia catheters (from Arrow International [Reading, Pennsylvania], B. Braun Medical Inc [Bethlehem, Pennsylvania], and Smiths Medical/Portex [Keene, New Hampshire]) for exposure to clinical 1.5- and 3-T MRI. Catheters testing as nonmagnetic were placed in an epidural configuration in a standard human torso-sized phantom, and an MRI pulse sequence applied at the maximum scanner-allowed radiofrequency specific absorption rate (SAR) for 15 minutes. Temperature and SAR exposure were sampled during MRI using multiple fiberoptic temperature sensors.

RESULTS

Two catheters (the Arrow StimuCath Peripheral Nerve and B. Braun Medical Perifix FX Epidural) were found to be magnetic and not tested further. At 3 T, exposure of the remaining 3 epidural and 1 peripheral nerve catheter to the scanner's maximum RF exposure elicited anomalous heating of 4°C to 7°C in 2 Arrow Epidural (MultiPort and Flex-Tip Plus) catheters at the entry points. Temperature increases for the other catheters at 3 T, and all catheters at 1.5 T were 1.4°C or less. When normalized to the body-average US Food and Drug Administration guideline SAR of 4 W/kg, maximum projected temperature increases were 0.1°C to 2.5°C at 1.5 T and 0.7°C to 2.7°C at 3 T, except for the Arrow MultiPort Flex-Tip Plus catheter at 3 T whose increase was 14°C.

CONCLUSIONS

Most but not all catheters can be left in place during 1.5-T MRI scans. Heating of less than 3°C during MRI for most catheters is not expected to be injurious. While heating was lower at 1.5 T versus 3 T, performance differences between products underscore the need for safety testing before performing MRI.

‘Talk and Die’ patients presenting to a major trauma centre over a 10 year period: A critical review

'Talk and die patients' describes a small number of patients who present with a mild head injury (Glasgow Coma Scale [GCS] 13-15) and then subsequently deteriorate and die from intracranial causes. We analysed the medical records of all those adult patients whose primary diagnosis as the cause of death was head injury, as determined by the coroner, who were admitted to a major Australian trauma centre between January 1994 and December 2003 (a 10-year period). The clinical profile of those patients who fulfilled the criteria of 'talk and die' were documented, including age, mode of injury, initial GCS, lucid interval, CT scan reports, operation performed, post mortem findings and intracranial cause of death. Factors considered potentially contributory to the patients' deterioration, such as delays in CT scanning or patient transfer, coagulopathy or hypoxic episodes were also noted. The incidence of 'talk and die' patients was 2.6% (15 out of 569) overall and the annual incidence did not significantly alter over the 10-year period of the study. The small number of patients precludes inferences regarding causal relationships, although potentially preventable factors, which could have been contributory to patient deterioration, were identified.

Central nervous system imaging. When is CT more appropriate than MRI?

Over the past 25 years, the development of noninvasive imaging techniques has allowed exquisite display of the anatomic structures of the brain and spinal cord in normal and disease states. CT remains useful because of short imaging times, widespread availability, ease of access, sensitive detection of calcification and hemorrhage, and resolution of bony detail. MRI offers superior soft-tissue contrast, excellent visualization of vascular structures, fewer artifacts, and imaging in any plane. Cost and use of ionizing radiation are considerations in choosing the most appropriate procedure. In the future, CT and MRI applications that concentrate on functional and physiologic display of the CNS will add greatly to the clinical utility of these imaging tools.

Advances in neurology

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Drug treatment of Alzheimer's disease. Effects on caregiver burden and patient quality of life

Alzheimer's disease is a devastating illness that will become more common as the population ages. Although clinical diagnosis of the illness is not certain without histological examination of the brain, and misdiagnosis may occur, broad working criteria to help diagnose the likely presence of Alzheimer's disease are available. Thoughtful clinical evaluation improves diagnostic accuracy, and appropriately diagnosed patients are critical for involvement in research into new antidementia agents. Essential to the discovery of new drugs is careful measurement of illness response. A variety of scales--some aimed at patients, others at their caregivers, and yet others for clinicians--assess Alzheimer's disease severity, progression, symptom response, and quality of life. Of note, patient response is not the only measurement of treatment benefit today. Growing interest is also being placed on tracking the possible amelioration of caregiver 'burden'. This burden refers to the psychological, physical, and material costs of providing care for an Alzheimer's patient over long periods of time. A number of scales and questionnaires have been developed and are occasionally used. Many drugs have been tried in Alzheimer's disease, but very few have produced any benefit, and this is often modest. Ergoloid mesylates, initially thought to be effective, are now considered of little value. The cholinomimetic drugs, especially the acetylcholinesterase inhibitor tacrine, have provided a very modest benefit, slowing the progression of the illness for a number of months. No cognitive improvement has been noted with the various nootropic agents such as piracetam. Early studies with levacecarnine (acetyl-L-carnitine), a substance that facilitates the use of fatty acids, memantidine, the dimethyl derivative of amantidine, and the calcium channel blocker nimodipine, have shown some promise, but require larger, more rigorous studies. As mentioned above, documenting effects in individual patients is crucial; examining for potential benefit to caregivers is a growing part of research design. Current treatment efforts will become more sophisticated as a deeper understanding of the neurobiology of Alzheimer's disease develops. For the immediate future, the goal is not cure but slowing of the disease process. Achieving this limited goal would have a substantial impact on the financial and human costs of the illness.

MR-imaging of non-Alzheimer's dementia

Up to now, computerized tomography (CT) and MR-imaging have been used for the morphological assessment of dementia patients, while MRI has become the structure imaging modality of choice. With the advent of fast and ultrafast sequences provided by higher gradient field strengths, functional MR studies like diffusion, perfusion and activation studies become available. The greatest advantage of MR is its versatility including MR-imaging, 3D postprocessing, MR-volumetry, MR-spectroscopy, MR-angiography, MR-perfusion and diffusion imaging as well as functional MRI activation studies. The application of the multimodal MR-technology in dementia disorders has already began and has to be validated in clinical practice. The multimodality of MR represents a diagnostic challenge for the future with the hope, that the diagnostic efficacy, which has to be proven, is also followed by an improvement of patients care and prognosis.

Cerebrospinal fluid

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