Computed Tomography Scout: Expediting Magnetic Resonance Imaging in Stroke Patients

Purpose: To investigate the utility of CT scout images in detecting potentially MRI-unsafe implants, devices, and objects.

Methods/Materials: 100 subjects with potentially MRI-incompatible objects (MIO) were selected, with both CT scout images and x-rays depicting the potential MIO. In addition, we included 100 controls with no potential MIOs, with CT scout images and x-rays of the same regions as the subjects. The controls and subjects were matched by gender, age, and body mass index (BMI). 408 imaging studies were included, 92 full-body CT scout images, 108 regional CT scout images, and 208 x-rays. The imaging studies of the subjects and controls were randomized and then interpreted by two board-certified neuroradiologists, one neuroradiology fellow, and three radiology residents, who were all blinded. They noted whether they believed potential MIOs were present, where they were located, and what they thought they were. A true positive was a response in which the presence of a potential MIO was detected, and the correct region was stated. The potential MIOs included joint prostheses, cardiac devices, vascular stents, bullets, embolization coils, aneurysm clips, jewelry, nerve stimulators, etc. The sensitivity, specificity, and accuracy of the full-body scouts, regional scouts, and x-rays were calculated with standard deviations (SD) and confidence intervals (CI).

Results: There were 51 males (51%) and 49 females (49%) in both the subjects and control groups. There were no significant differences between the ages and BMI of the subject and controls (p>0.4). For full-body CT scout images, the sensitivity was 82.54%, specificity 98.55%, and accuracy 90.56% (95% CI 89.65%, 91.47%). For regional CT scout images, the sensitivity was 83.64%, specificity 99.69%, and accuracy 91.65% (95% CI: 89.48%, 93.82%). For x-rays, the sensitivity was 88.78%, specificity 99.84%, and accuracy 94.30% (95% CI: 92.76%, 95.85%). (Table 1)

Conclusions: Full-body or regional CT scout images can be employed in CT head protocols for acute stroke to detect potentially MRI-unsafe implants, devices, and objects, which can help expedite MRI in stroke patients.