Diffusion- and perfusion-weighted MRI (DWI and PWI) can image apparent changes in proton motion and in cerebral perfusion patterns. High-speed methods reduce motion artifacts, in imaging rapid time-resolved hemodynamic changes, and in maximizing diffusion-modulated and susceptibility-modulated T2 tissue contrasts. DWI and PWI are hampered by artifacts due to patient motion. High speed MRI can """"""""freeze out"""""""" patient motion, where minimizing the time required to obtain DWI and PWI is preferable. PWI rapidly acquires images following bolus injection of contrast. The contrast can be detected as it passes through the capillary beds. Magnetic-susceptibility contrast agents such as Gadolinium-DTPA assess changes in tissue perfusion by inducing a T2* shortening in perfused tissue. The passage of the contrast agent can then give information on the hemodynamic status of the tissue. Methods and Results A commercially available high-speed MRI (EPI) upgrade has been added to our research and hospital scanners. This has allowed us to develop and test single-shot EPI sequences capable of obtaining images on the order of 64 msec. We are able to obtain 8-12 axial images with 8 diffusion-weighted bvalues spaced equally between 0-800 sec/m2. This is repeated in each of the three principal magnet directions and has a total imaging time of 40 seconds for 10 multislice sets.. For PWI (Figure 21), we use a similar protocol to the ungated single shot spin echo EPI sequence used for DWI. Scanning is done concomitantly with a bolus injection of 0.1 mmol/kg Gd DTPA given over 3-5 seconds. Discussion A combination of fast DWI and PWI methods creates the possibility of rapidly and repeatedly scanning patients where clinical decisions can be made directly from the images and the effects of treatment seen immediately.
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