OBJECTIVE: To select the best mathematical algorithms for lumbar spine imaging studies to assess arthrodesis with metal implant. MATERIALS E METHODS: The images acquisition was performed with a multidetector (16 rows) CT scanner, and 2 mm and 4 mm slice thickness. Images of ten patients were reconstructed with filters 20, 40, 60 and 80, employing multiplanar three-dimensional volume-rendering techniques. A total of 320 images were evaluated by three experienced radiologists who rated the images from 1 to 5 (1 = unacceptable; 2 = substandard; 3 = acceptable; 4 = above the average; 5 = excellent). Additionally, noise measurements were performed for correlation with the type of filter utilized. RESULTS: For 2 mm thickness and filters 20, 40, 60 e 80, mean noise measurements for images reconstruction were, respectively, 24.7 ± 4.3, 35.5 ± 4.2, 106.0 ± 18.5 and 145.9 ± 26.9, and for 4 mm and filters 20, 40, 60 and 80 were, respectively, 18.1 ± 2.4, 25.1 ± 4.6, 76.7 ± 17.2 and 106.6 ± 23.4. CONCLUSION: Three-dimensional color images could be better visualized with filter 20; however, in the case of gray-scale, filters 40 or 60 could be useful to demonstrate the arthrodesis pedicle screws in higher detail. For multiplanar reconstructions with 2 mm slice thickness, the filter 40 was the most appropriate, and for 4 mm, a filter 60 presented a better image quality.

Keywords: Computed tomography, Arthrodesis, Lumbar spine, Image quality

OBJECTIVE: To reduce radiation dose and increase x-ray tube life in computed tomography. MATERIALS AND METHODS: Head, upper abdomen and chest scans were evaluated. We assessed the techniques employed and if these could be changed, suggested new protocols and compared the quality of the images, the radiation dose and the x-ray tube heating. RESULTS: A mAs reduction could be done without interfering with the diagnostic quality, allowing a decrease of up to 20% in the average dose for adults' head exams and up to 45% for 0 to 6 years old children; patients with less than 50 kg had a reduction of 37% on the upper abdomen radiation average dose; for chest routine scans the reduction was 54%. The decrease in the heating of the x-ray tube for head, upper abdomen and chest scans was approximately 13%, 23% and 41%, respectively. CONCLUSION: A change on the described protocols will produce a significant reduction on the radiation dose and an increasing in x-ray tube life without loss of diagnostic quality.

Keywords: X-ray computed tomography, Radiation exposure, Radiation dosage, Radiation protection