Improvement on detectability of early ischemic changes for acute stroke using nonenhanced computed tomography: effect of matrix size.

PURPOSE It has recently been reported that intravenous recombinant tissue plasminogen activator improves the clinical outcome after acute stroke. Computed tomography (CT) is the standard imaging method used to determine the indication for thrombolysis. However, detection of early ischemic change often results in an increase in local radiation exposure. Therefore, the effects of decreased matrix size and use of a noise reduction filter were evaluated. MATERIALS AND METHODS The low contrast resolution was compared for different matrix sizes and imaging filters using a contrast-detail phantom. In addition, early ischemic change in clinical images with matrix sizes of 256×256 and 128×128 processed using three imaging filters (Gaussian, smoothing, and unsharp mask) from 11 patients within 3h of stroke onset was evaluated by seven radiologists in a blind manner. RESULTS The use of images with a matrix size of 256×256 and processed with the Gaussian filter increased the detection of early signs of acute stroke. CONCLUSIONS This study was performed to determine whether the converted matrix size and use of imaging filters could improve the detectability of early ischemic change on CT images in acute stroke. To reduce the dose of radiation exposure for patients, it was effective to use an optimal noise reduction filter and reasonable matrix size. In particular, changing the matrix size to 256×256 was the most effective for detection of early ischemic change in examinations using clinical images.