H J Laubach | PubMed Health

PubMed1998

[Diffusion-weighted imaging in acute stroke].

Magnetic resonance imaging represents today the most important tool in neuroradiology for both clinical practice and research. MRI allows imaging of the human body in 2 or 3 dimensions with variable tissue contrast. The natural diffusion of tissue protons can now be used as a supplementary contrast mechanism. Different MRI techniques can be used to obtain clinically useful diffusion-weighted images. These techniques all require the use of strong gradient pulses in order to obtain the diffusion contrast. In the current article, the most important physical principles of diffusion measurement are presented. After a short introduction into the basic physical principles, we will present the prerequisites and limitations of clinically relevant applications today. Finally a few select examples of clinical use of these techniques in the acute diagnosis of stroke will be presented.

Acute Disease↗

PubMedDate not supplied

A phantom for diffusion-weighted imaging of acute stroke.

A tissue phantom for diffusion-weighted imaging was developed, basing its contrast between two compartments on different apparent diffusion coefficients, without contrast due to T2 relaxation and proton density. These contrast properties of the phantom simulate the situation found in normal gray matter and areas of acute ischemia. A possible application of the phantom was demonstrated for the investigation of the accuracy of volume measurements based on diffusion-weighted images.

Acute Disease↗

PubMedDate not supplied

Clinical experience with diffusion-weighted MR in patients with acute stroke.

PURPOSE: Our purpose was to evaluate the clinical efficacy, sensitivity, and specificity of echo-planar diffusion-weighted MR imaging in patients with acute infarction. METHODS: We retrospectively analyzed 194 cases of acute ischemic stroke diagnosed clinically within 24 hours of onset and studied with echo-planar diffusion-weighted MR imaging. Examinations were considered to be positive for infarction when an increase in signal was noted on images acquired at a high b value but absent on images with a low b value. A final clinical diagnosis of acute stroke was used as the standard of reference. A subset of 48 patients scanned within 6 hours was also analyzed. RESULTS: Diffusion-weighted MR imaging studies were positive in 133 of 151 cases of infarction (88% sensitivity) and negative in 41 of 43 cases with no infarction (95% specificity). Two cases identified as positive on diffusion-weighted images had nonischemic diagnoses (1.5% false-positive rate). Diffusion-weighted imaging had a positive predictive value of 98.5% and a negative predictive value of 69.5%. Use of T2-weighted sequences as well as diffusion-weighted imaging produced no false-positive findings. Of the negative scans, 69.5% corresponded to transient ischemic attacks or infarcts (mostly small brain stem infarcts). When only cases scanned within 6 hours of onset were considered, the sensitivity rose to 94% and the specificity to 100%. CONCLUSION: Despite bias due to dependence between diffusion-weighted imaging and the final diagnosis, this analysis suggests high sensitivity and specificity for echo-planar diffusion-weighted imaging in the diagnosis of acute cerebral infarction, although negative scans did not rule out an ischemic pathogenesis.

Acute Disease↗