Optimizing dose reduction in CT scanning of the paranasal sinuses: A randomized control trial of recommended versus lowest achievable dose protocols

A comparison between low-dose and standard-dose non-contrasted multidetector CT scanning of the paranasal sinuses

PURPOSE

To compare the image quality of the low-dose to the standard-dose protocol of MDCT scanning of the paranasal sinuses, based on subjective assessment and determine the radiation doses to the eyes and thyroid gland and dose reduction between these two protocols.

MATERIALS AND METHODS

31 adult patients were scanned. Prior to scanning, thermoluminescent dosimeters (TLDs) were placed at 4 sites: outer canthus of right eye, outer canthus of left eye, inner canthus and anterior neck (thyroid gland). Every patient was scanned twice using the standard-dose protocol (100mAs) followed by the low-dose protocol (40mAs). The images were reviewed by 3 radiologists. Wilcoxon test was used as the test of significance for the image quality assessments. The paired sample t-test was used as the test of significance for the analysis of the radiation doses measured by the TLDs.

RESULTS

Of the 30 patients selected for analysis, this study showed no significant difference in the scores for the diagnostic image quality and the anatomical structures assessments between the two protocols. The average calculated mean entrance surface doses and standard deviation for the standard-dose and low-dose protocols were 12.40±1.39 mGy and 5.53±0.82 mGy respectively to the lens and 1.03±0.55 mGy and 0.63±0.53 mGy respectively to the thyroid gland.

CONCLUSION

The reduction of mAs from 100 to 40 resulted in a significant reduction of the radiation doses to the lens and thyroid gland by 55.4% and 38.8% respectively without causing any significant effect to the diagnostic image quality and assessment of the anatomical structures.

State-of-the-Art computed tomography of primate skulls — Comparison of different scan-protocols

To evaluate the image quality of different scan-protocols on 3 different CT-scanners for data acquisition of skulls of apes and monkeys with special respect on imaging the paranasal sinuses, we compared CT image quality in 452 skulls on either the Philips "Mx8000" Multi-Slice CT, the "Aura" Spiral CT or the "T omoscanM" CT scanner. Therefore, we used sequential and volume scanning as well as different slice thickness, table feed, voltage and X-ray current intensity. Representative axial scans of the anonymized studies as well as three-dimensional reconstructions were independently analyzed by an experienced radiologist and an anthropologist, using a study protocol covering relevant anatomical findings. Low-Dose protocols at 40 mAs demonstrated an equal diagnostic value with better CT-performance due to lower overheatening of the X-ray tube in all studies. Resolution, especially in small anatomical structures, was best with multi-slice CT. On both single-slice scanners resolution was significantly better with sequential-protocols (slice 2-5 mm; feed 1:1) than with volume-protocols. Volume scans are required for 3D-reconstruction. Best 3D results were achieved with "M x8000" due to its better spatial resolution, followed by the "Aura" scanner. Multi-slice CT (MSCT) was found to be the superior method for the radiographic evaluation of small anatomical structures. However, there is no significant loss of information with thin sequential scans in LD technique on a single-slice spiral CT scanner. Volume-data aquisition is required for 3D reconstruction.