ALL IN THE HEAD
Image 5 : MRI Diffusion weighted image ( DWI ) left and ADC map right : Acute right MCA infarct . Image courtesy of frontal cortex . com .
Image 6 : Normal DAT Scan : Normal bilateral uptake in the caudate nucleus and putamen . Image courtesy of NINDS and NIH .
Image 7 : Normal MRA neck with contrast . Image courtesy of Radiopaedia .
to assess the extent of resection of some brain tumors in real time .
The next milestone was reached when clinical MRI scanners were made available in the early 1980s . High quality imaging of the CNS was now obtained without the use of X-rays . Strong magnetic fields and radio frequency energy were used to generate signals and ultimately images from the hydrogen in water , fat and other body molecules . Direct high-resolution neuroimaging now was available without radiation .
Multiplanar and multisequence images could be obtained to further characterize brain and spinal cord normal anatomy and pathology . For example , fluid attenuated inversion recovery ( FLAIR ) imaging is useful to detect edema , gliosis and MS plaques . Diffusion weighted imaging ( DWI ) is the gold standard for detecting acute stroke . ( Image 5 ) It is available on all current MRIs and can be obtained in less than a minute . Susceptibility weighted imaging ( SWI ) is a 3D high resolution gradient echo sequence sensitive to blood , blood breakdown products and minerals such as calcium .
Higher field strength 3 Tesla ( 3T ) magnets , improved surface coils and evolving software programs and computer technology
have resulted in higher resolution images with increased signal . MR angiography ( MRA ) of the brain and neck , MR venography ( MRV ) of the head , dynamic post contrast imaging , MR perfusion ( MRP ), MR spectroscopy ( MRS ), and functional MRI ( fMRI ) are currently available . For example , fMRI can be used to noninvasively map eloquent brain cortex prior to epilepsy or brain tumor surgery .
Many high-resolution 3D image sequences have been developed for specific indications . Millimeter and sub-millimeter axial images and reformatted images are readily obtained . A heavily T2 weighted sequence can be used to evaluate the internal auditory canal for small vestibular schwanommas in patients with a contraindication to contrast . It can be used to exclude vascular compression in trigeminal neuralgia and hemifacial spasm syndromes . One millimeter post contrast T1 weighted 3D sequences are routinely obtained . This sequence is used to detect subtle foci of pathologic contrast enhancement and can evaluate the dural venous sinuses . Also , these sequences can be merged with software programs for surgical and radiation therapy planning .
MRI safety and thorough patient screening are more important now than ever in 2020 as the list of implantable electronic devic-
8 LOUISVILLE MEDICINE