Observer Performance with Varying Radiation Dose and Reconstruction Methods for Detection of Hepatic Metastases

Abstract

Purpose: To estimate the ability of lower dose levels and iterative reconstruction (IR) to display hepatic metastases that can be detected by radiologists. Materials and Methods: Projection data from 83 contrast agent–enhanced CT examinations were collected. Metastases were defined by histopathologic analysis or progression and regression. Lower radiation dose configurations were reconstructed at five dose levels with filtered back projection (FBP) and IR (automatic exposure control settings: 80, 100, 120, 160, and 200 quality reference mAs [QRM]). Three abdominal radiologists circumscribed metastases, indicating confidence (confidence range, 0–100) and image quality. Noninferiority was assessed by using jackknife alternative free-response receiver operating characteristic (JAFROC) analysis (noninferiority limit, −0.10) and reader agreement rules, which required identification of metastases identified at routine dose, and no nonlesion localizations in patients negative for metastases, in 71 or more patient CT examinations (of 83), for each configuration. Results: There were 123 hepatic metastases (mean size, 1.4 cm; median volume CT dose index and size-specific dose estimate, 11.0 and 13.4 mGy, respectively). By using JAFROC figure of merit, 100 QRM FBP did not meet noninferiority criteria and had estimated performance difference from routine dose of −0.08 (95% confidence interval: −0.11, −0.04). Preset reader agreement rules were not met for 100 QRM IR or 80 QRM IR, but were met for doses 120 QRM or higher (ie, size-specific dose estimate ≥ 8.0 mGy). IR improved image quality (P < .05) but not reader performance. Other than 160 QRM IR, lower dose levels were associated with reduced confidence in metastasis detection (P < .001). Conclusion: For detection of hepatic metastases by using contrast-enhanced CT, dose levels that corresponded to 120 quality reference mAs (size-specific dose estimate, 8.0 mGy) and higher performed similarly to 200 quality reference mAs with filtered back projection.

A Universal Protocol for Abdominal CT Examinations Performed on a Photon-Counting Detector CT System

“…The cylindrical holes were filled with iodinated contrast material (iohexol, Omnipaque 350; GE Healthcare Ireland, Cork, Ireland) to mimic low-contrast enhancing liver lesions that are commonly seen in patients. 34 The iodine solution was diluted to yield 4 concentrations (0.2, 0.5, 1.0, and 2.0 mg I/mL) to simulate lesions of various enhancement levels (CT number difference from the tissueequivalent background of 4.5, 11.1, 22.0, and 44.2 HU at 120 kV, respectively). The 4 iodine concentrations were based on the reported thresholds, as low as 0.3 mg I/mL, for distinguishing clinically relevant contrast-enhanced pathologies using DECT technology.…”

Evaluation of Lower-Dose Spiral Head CT for Detection of Intracranial Findings Causing Neurologic Deficits

“…Iterative reconstruction (IR) can provide noninferior performance for high-contrast detection tasks at lower doses; however, recent data in phantoms and abdominal CT suggest that the improvement in observer performance compared with filtered back-projection (FBP) may be limited. [8][9][10][11] Most studies examining lower-dose head CT with iterative reconstruction have relied on subjective comparisons of image quality or contrast-to-noise ratios rather than observer (ie, radiologist) performance. Practical considerations such as collecting cases with proven imaging findings, obtaining CT images at multiple doses, and correlating imaging findings between dose levels and reference standards make such research challenging.…”

“…Preset criteria for prioritization of a lower-dose configuration were agreement with routine dose interpretation in 71 of the 83 cases (86% of examinations). 8 JAFROC FOM analysis used the reader confidence scores input by the readers as well as their circumscribed imaging findings. A full description of JAFROC FOM for a mixed population as in this study has been provided previously.…”

“…Jensen et al 11 found that an approximately 50% dose reduction with one iterative reconstruction approach did not preserve observer performance for the detection of hepatic metastases. Fletcher et al 8,12 found that FBP and IR performed similarly at lower doses in detecting hepatic metastases and that IR might only be needed to maintain observer performance at a certain threshold dose. Similar to these studies, we found that performance for the detection of intracranial findings causing acute neurologic deficits declined slightly at lower doses using JAFROC FOM as a metric of observer performance but that iterative reconstruction was helpful in preserving noninferiority at 100 eff.…”

Performance Evaluation of Two Iterative Reconstruction Algorithms--MBIR and ASIR, in Low Radiation Dose and Low Contrast Dose Abdominal CT in Children

“…As low-kV imaging can increase the absorption of iodide ions to improve the enhancement effect of iodine contrast agents [4], it is often used in the "double-low" CT scans. Iterative reconstruction (IR) has been used in the "double low" CT to reduce image noise and to meet the diagnostic requirements and has been applied to CT applications in chest, abdomen, blood vessel and other areas [5][6][7][8][9][10][11]. In addition, relevant studies have shown that the more sophisticated full model-based iterative reconstruction (MBIR) algorithm is more powerful than the adaptive statistical iterative reconstruction (ASIR) in image noise reduction [12][13][14][15][16][17].…”