Reducing Radiation Dose at CT Colonography: Decreasing Tube Voltage to 100 kVp

Abstract

Purpose:To assess the effect of a decrease in tube voltage from 120 kVp to 100 kVp on dose, contrast-to-noise ratio (CNR), and three-dimensional (3D) image quality in patients undergoing computed tomographic (CT) colonography as well as to determine how these changes are affected by patient size. Materials and Methods:This HIPAA-compliant and institutional review board-approved retrospective study included 63 consecutive patients who underwent CT colonography and who waived informed consent. Scanning was performed with patients in the supine (120 kVp) and prone (100 kVp) positions, with other parameters unchanged. Volume CT dose index (CTDI vol ), dose-length product (DLP), image noise, attenuation of selected materials, and CNR were compared with the Wilcoxon matched-pairs signed rank test. Two readers blinded to tube voltage independently assessed 3D endoluminal image quality. The k coefficients were calculated for interobserver agreement. Average image quality ratings were compared with the Wilcoxon signed rank test. All recorded data were stratified by patient anteroposterior diameter to determine effects of patient size. Results:Decreasing tube voltage from 120 to 100 kVp resulted in a 20% decrease in CTDI vol (P , .001) and a 16% decrease in DLP (P , .001). Image noise increased by 32% (P , .001). Mean attenuation of tagged fluid increased from 395 to 487 HU (P , .001). There was no change in mean CNR of tagged fluid (17.1 at 120 kVp, 16.8 at 100 kVp; P = .37), regardless of patient size. The 3D image quality decreased slightly from a median score of 5 out of 5 to 4 out of 5 (P , .001). There was substantial interobserver agreement. Conclusion:A decrease in tube voltage from 120 to 100 kVp results in a significant decrease in radiation dose but only a minimal decrease in 3D image quality at all patient sizes.q RSNA, 2012

Reducing the Radiation Dose for CT Colonography

“…Chang et al (7) who first assessed the effect of low tube voltage on the image quality at CTC demonstrated that the 100-kVp CTC protocol with FBP allowed for a reduction in CTDI vol by 20% and of DLP by 16%. However, their study showed a decrease in the 3D image quality and did not include IR.…”

“…However, increased image noise, a byproduct of low-tube-voltage settings, is a serious problem (6). Chang et al (7) assessed the effect of lowtube-voltage techniques on the image quality of CTC in 63 patients. They found that a decrease in the tube voltage from 120 to 100 kVp with filtered back projection (FBP) resulted in a significant decrease in the radiation dose and a decrease in the three-dimensional (3D) image quality.…”

Model-basedvshybrid iterative reconstruction technique in ultralow-dose submillisievert CT colonography

“…13 Our initial attempts to use low-energy scanning at 100 kV peak tube voltage that may otherwise be used to decrease the radiation dose by 20% were discouraging, because in a submillisievert region, it contributed to increased image noise to a greater extent than what could be compensated by increasing the tube current while maintaining low radiation dose. 8,14 A 140-kV protocol used with a 10-mAs time-current product and FBP results in a 1.8-to 2.4-mSv radiation dose and ensures excellent sensitivity for detection of relevant ($6 mm) lesions. 6 However, in our specific scanner, the reference timecurrent product cannot be set to ,10 mAs and therefore the 140-kV protocol was not used.…”

“…4 Further reduction of the radiation dose while maintaining diagnostic acceptability requires special considerations regarding acquisition and image-processing techniques. [7][8][9] In particular, new developments in the field of iterative reconstruction offer further reduction of the radiation dose with preserved image quality. 7,10 The objective of this study was to compare image quality of different reconstruction techniques in a submillisievert ultralow-dose CTC in order to assess image quality and recommend the most applicable technique.…”

CT colonography at low tube potential: using iterative reconstruction to decrease noise

“…In addition, at a lower tube potential, the average energy of the X-ray beam more closely approaches the K-edge of iodine leading to an increase in attenuation of iodinated contrast medium. 20 The use of a lower tube potential to reduce radiation dose and increase the contrast medium attenuation of tagged colonic fluid has already been demonstrated in CTC 21 as well as multiple other contrast-enhanced applications 17,22e28 ; however, in one study, the decrease in tube potential from 120 to 100 kVp resulted in a 32% increase in image noise. 21 Iterative reconstruction methods such as adaptive statistical iterative reconstruction (ASiR, GE Healthcare, Waukesha, WI, USA) use an alternative method of reconstructing CT data that reduces image noise while preserving edge detail 29,30 when compared to filtered back projection.…”