Detection of Colorectal Hepatic Metastases Is Superior at Standard Radiation Dose CT versus Reduced Dose CT

Abstract

Purpose To evaluate colorectal cancer hepatic metastasis detection and characterization between reduced radiation dose (RD) and standard dose (SD) contrast material-enhanced CT of the abdomen and to qualitatively compare between filtered back projection (FBP) and iterative reconstruction algorithms. Materials and Methods In this prospective study (from May 2017 through November 2017), 52 adults with biopsy-proven colorectal cancer and suspected hepatic metastases at baseline CT underwent two portal venous phase CT scans: SD and RD in the same breath hold. Three radiologists, blinded to examination details, performed detection and characterization of 2-15-mm lesions on the SD FBP and RD adaptive statistical iterative reconstruction (ASIR)-V 60% series images. Readers assessed overall image quality and lesions between SD FBP and seven different iterative reconstructions. Two nonblinded consensus reviewers established the reference standard using the picture archiving and communication system lesion marks of each reader, multiple comparison examinations, and clinical data. Results RD CT resulted in a mean dose reduction of 54% compared with SD. Of the 260 lesions (233 metastatic, 27 benign), 212 (82%; 95% confidence interval [CI]: 76%, 86%) were detected with RD CT, whereas 252 (97%; 95% CI: 94%, 99%) were detected with SD (P < .001); per-lesion sensitivity was 79% (95% CI: 74%, 84%) and 94% (95% CI: 90%, 96%) (P < .001), respectively. Mean qualitative scores ranked SD images as higher quality than RD series images, and ASIR-V ranked higher than ASIR and Veo 3.0. Conclusion CT evaluation of colorectal liver metastases is compromised with modest radiation dose reduction, and the use of iterative reconstructions could not maintain observer performance. © RSNA, 2018.

Trial registration: ClinicalTrials.gov NCT03151564.

Figure 1:

Flowchart of participant accrual.

Figure 2:

Graph shows results of qualitative image evaluation of overall image quality rank. A score of 0 was given for the best series, −1 for slightly inferior (no influence on diagnosis), −2 for mildly inferior (possible influence on diagnosis), −3 for moderately inferior (probable influence on diagnosis), and −4 for markedly inferior (impairing diagnosis). Mean image quality rank was significantly different from the next best reconstruction except between the standard dose (SD) and reduced dose (RD) adaptive statistical iterative reconstruction AV60/AV30 reconstructions (P = .89) and the SD filtered back projection (FBP)/SD A80 reconstructions (P = .57). A80 = adaptive statistical iterative reconstruction (ASIR) 80%, AV30/60 = ASIR-V 30%/60%.

Figure 3:

Axial contrast-enhanced CT images show example of two small low-contrast liver metastases (arrows) that were seen by all three readers during the evaluation of standard radiation dose (SD) filtered back projection (FBP) images but were missed during the evaluation of reduced dose (RD) adaptive statistical iterative reconstruction–V 60% (AV60) images.

Figure 4:

Axial contrast-enhanced CT images of the abdomen show qualitative comparison of a low-contrast left hepatic metastasis (arrow and circle, arrow) between standard radiation dose (SD) and reduced dose (RD) scans obtained in the same breath hold during the current study. Readers ranked the AV60 reconstruction highest in their respective SD and RD scan groups. FBP = filtered back projection, A80 = adaptive statistical iterative reconstruction (ASIR) 80%, AV30 = ASIR-V 30%, AV60 = ASIR-V 60%.