Whole-body low-dose computed tomography image quality and radiation dose in multiple myeloma: A comparison between 64-slice and 128-slice scanners

Objectives: The objectives of the study are to compare radiation dose and objective image quality between whole- body low-dose computed tomography (WBLDCT) examinations performed on 64-slice and 128-slice scanners in patients with multiple myeloma. Material and Methods: This retrospective, single-center observational study included two independent cohorts: 16 patients imaged on a 64-slice scanner, and 16 different patients imaged on a 128-slice scanner. Each scanner used its own clinical protocol. Objective image quality was assessed using signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measurements at the frontal spongy bone, occipital compact bone, and right femoral shaft. Image noise was the standard deviation (SD) of attenuation within an air region of interest. Radiation dose was assessed using dose-length product (DLP), with estimated effective dose calculated using a conversion factor of 0.015 mSv/(mGy•cm). Independent-group comparisons were performed using the Mann– Whitney U test or Welch independent samples t -test, as appropriate. The Holm method was used to adjust the six image-quality comparisons for multiple testing. Results: The 128-slice scanner demonstrated higher SNR and CNR values at all assessed skeletal sites. Improvements were statistically significant at the frontal spongy bone (SNR, p = 0.0019; CNR, p = 0.0027), occipital compact bone (SNR, p = 0.0004; CNR, p = 0.0004), and right femoral shaft (SNR, p = 0.0006; CNR, p = 0.0010), and all six remained significant after Holm adjustment. Mean DLP was significantly lower with the 128-slice scanner than with the 64-slice scanner (328.9 mGy•cm SD 121.0) compared with 638.2 mGy•cm (SD 101.0); mean difference −309.3 mGy•cm (95% confidence interval −389.9–−228.7); p < 0.0001), corresponding to a reduction in mean estimated effective dose from 9.57 to 4.93 mSv. Mean volume computed tomography dose index was 4.39 mGy for the 64-slice scanner and 2.26 mGy for the 128-slice scanner. All 64-slice examinations used 140 kV, and 128-slice examinations used 100 or 120 kV. Conclusion: In this cohort, WBLDCT performed on the 128-slice scanner was associated with improved objective image quality and lower radiation dose compared with the 64-slice scanner. These differences cannot be attributed to slice count alone because the two scanners used different protocols, including a lower tube voltage on the 128-slice scanner.