Development and Evaluation of an Automated Protocol Recommendation System for Chest CT Using Natural Language Processing With CLEVER Terminology Word Replacement.

Purpose: To evaluate the clinical performance of a Protocol Recommendation System (PRS) automatic protocolling of chest CT imaging requests. Materials and Methods: 322 387 consecutive historical imaging requests for chest CT between 2017 and 2022 were extracted from a radiology information system (RIS) database containing 16 associated patient information values. Records with missing fields and protocols with <100 occurrences were removed, leaving 18 protocols for training. After freetext pre-processing and applying CLEVER terminology word replacements, the features of a bag-of-words model were used to train a multinomial logistic regression classifier. Four readers protocolled 300 clinically executed protocols (CEP) based on all clinically available information. After their selection was made, the PRS and CEP were unblinded, and the readers were asked to score their agreement (1 = severe error, 2 = moderate error, 3 = disagreement but acceptable, 4 = agreement). The ground truth was established by the readers' majority selection, a judge helped break ties. For the PRS and CEP, the accuracy and clinical acceptability (scores 3 and 4) were calculated. The readers' protocolling reliability was measured using Fleiss' Kappa. Results: Four readers agreed on 203/300 protocols, 3 on 82/300 cases, and in 15 cases, a judge was needed. PRS errors were found by the 4 readers in 1%, 2.7%, 1%, and 0.7% of the cases, respectively. The accuracy/clinical acceptability of the PRS and CEP were 84.3%/98.6% and 83.0%/99.3%, respectively. The Fleiss' Kappa for all readers and all protocols was 0.805. Conclusion: The PRS achieved similar accuracy to human performance and may help radiologists master the ever-increasing workload.

Chest CT at X-Ray Dose Using a Noise-Mitigating Weighted Projection: The Thoracic Tomogram. Diagnostic Performance for Pneumonia Detection in Hemato-Oncology Patients.

PURPOSE: To compare the diagnostic performance of a thick-slab reconstruction obtained from an ultra-low-dose CT (termed thoracic tomogram) with standard-of-care low-dose CT (SOC-CT) for rapid interpretation and detection of pneumonia in hemato-oncology patients. METHODS: Hemato-oncology patients with a working diagnosis of pneumonia underwent an SOC-CT followed by an ultra-low-dose CT, from which the thoracic tomogram (TT) was reconstructed. Three radiologists evaluated the TT and SOC-CT in the following categories: (I) infectious/inflammatory opacities, (II) small airways infectious/inflammatory changes, (III) atelectasis, (IV) pleural effusions, and (V) interstitial abnormalities. The TT interpretation time and radiation dose were recorded. Sensitivity, specificity, diagnostic accuracy, ROC, and AUC were calculated with the corresponding power analyses. The agreement between TT and SOC-CT was calculated by Correlation Coefficient for Repeated Measures (CCRM), and the Shrout-Fleiss intra-class correlations test was used to calculate interrater agreement. RESULTS: Forty-seven patients (mean age 58.7 ± 14.9 years; 29 male) were prospectively enrolled. Sensitivity, specificity, accuracy, AUC, and Power for categories I/II/III/IV/V were: 94.9/99/97.9/0.971/100, 78/91.2/86.5/0.906/100, 88.6/100/97.2/0.941/100, 100/99.2/99.3/0.995/100, and 47.6/100/92.2/0.746/87.3. CCRM between TT and SOC-CT for the same categories were .97/.81/.92/.96/.62 with an interobserver agreement of .93/.88/.82/.96/.61. Mean interpretation time was 18.6 ± 5.4 seconds. The average effective radiation dose of TT was similar to a frontal and lateral chest X-ray (0.27 ± 0.08 vs 1.46 ± 0.64 mSv for SOC-CT; P < .01). CONCLUSION: Thoracic tomograms provide comparable diagnostic information to SOC-CT for the detection of pneumonia in immunocompromised patients at one-fifth of the radiation dose with high interobserver agreement.

Chemoradiotherapy Using Carboplatin plus Paclitaxel versus Cisplatin plus Fluorouracil for Esophageal or Gastroesophageal Junction Cancer.

BACKGROUND: Trimodality therapy (TMT) with neoadjuvant chemoradiotherapy (nCRT) using concurrent carboplatin plus paclitaxel (CP) followed by surgery is the standard of care for locoregional esophageal or gastroesophageal junction (GEJ) cancers. Alternatively, nCRT with cisplatin plus fluorouracil (CF) can be used. Definitive chemoradiotherapy (dCRT) with CP or CF can be used if surgery is not planned. In the absence of comparative trials, we aimed to evaluate outcomes of CP and CF in the settings of TMT and dCRT. METHODS: A single-site, retrospective cohort study was conducted at the Princess Margaret Cancer Centre to identify all patients who received CRT for locoregional esophageal or GEJ cancer. Overall survival (OS) and disease-free survival (DFS) were assessed using the Kaplan-Meier method and multivariable Cox regression model. The inverse probability treatment weighting (IPTW) method was used for sensitivity analysis. RESULTS: Between 2011 and 2015, 93 patients with esophageal (49%) and GEJ (51%) cancers underwent nCRT (n = 67; 72%) or dCRT (n = 26; 28%). Median age was 62.3 years and 74% were male. Median follow-up was 23.9 months. Comparing CP to CF in the setting of TMT, the OS and DFS rates were similar. In the setting of dCRT, CP was associated with significantly inferior 3-year OS (36 vs. 63%; p = 0.001; HR 3.1; 95% CI: 1.2-7.7) and DFS (0 vs. 41%; p = 0.004; HR 3.6; 95% CI: 1.4-8.9) on multivariable and IPTW sensitivity analyses. CONCLUSIONS: TMT with CF and CP produced comparable outcomes. However, for dCRT, CF may be a superior regimen.

Hepatic Arterial Blood Flow Modulation in Patients with Hepatocellular Carcinoma: A Pilot Study of the Influence of Intraarterial Norepinephrine Assessed with CT Perfusion.

PURPOSE: This pilot study aims to evaluate the effect of hepatic intraarterial norepinephrine injection in vasculature modulation for hepatocellular carcinoma (HCC) tumors. MATERIALS AND METHODS: This is a single-center prospective study of patients with HCC with proven single-lobe tumors > 3 cm. Eight patients were included, with a mean age of 63 y ± 8. All patients had Barcelona Clinic Liver Cancer stage B HCC and an Eastern Cooperative Oncology Group performance status of 0. Mean tumor size was 6.1 cm ± 1.8; all tumors were hypervascular. Patients underwent CT hepatic perfusion before and after injection of 24 µg of norepinephrine intraarterially (4 µg/mL; total 6 mL injected at a rate of 1 mL/s). Color-coded perfusion maps were used to assess the effects of local therapy on hepatic perfusion values. Tumor-to-liver ratio (TLR) was calculated from the ratio of tumor perfusion to background liver perfusion value. RESULTS: Seven of 8 patents had significant (P = .04) absolute increase in tumor perfusion vs background liver, varying from incremental (-2 mL/min/100 mL) to 290 mL/min/100 mL. There was a nonsignificant increase in TLR from 2.7 ± 1.3 to 2.9 ± 1.4 after norepinephrine injection (P = .8). Mean peak time to maximal increase in tumor perfusion after injection was 6.1 s (range, 4.5-9.1 s). Norepinephrine injection was well tolerated without major adverse events. CONCLUSIONS: Norepinephrine causes increased blood flow toward HCC tumors, but with a corresponding smaller increase in blood flow to noncancerous liver tissue, with no observed systemic side effects.

Ultra-low dose CT abdomen and pelvis for the detection of acute abdominal pathology in the emergency room: initial experience from an academic hospital.

PURPOSE: The aim of this study is to describe our initial experience using ULDCT performed in the emergency room in the evaluation of acute abdominal pathology. METHODS: Data from consecutive patients who underwent ULDCT for assessment of bowel obstruction, free intraperitoneal air, unexplained abdominal pain, or fecal loading for constipation between June 1, 2016 and March 31, 2017 was retrospectively assessed. Demographic data, radiation dose, CT findings, and clinical outcomes including performance of full dose contrast-enhanced CT (CECT), hospitalization, and surgery was collected. Concordance of ULDCT to CECT was calculated. RESULTS: ULDCT was performed in 325 patients (188 women and 137 men; mean age, 65.1 years). ULDCT detected acute abdominal pathology in 134/325 (41.2%), and in 89/134 (66.4%) it was concordant with the clinical working diagnosis. The average dose length product (DLP) was 101.6 mGy cm (range 51.7-614; median, 82.6). CECT was performed in 44/325 patients (13.5%). In 7/44 (15.9%), CECT identified discordant findings which likely impacted management. A greater proportion of patients were admitted to hospital after a positive ULDCT 99/137 (72.3%), compared to those with a negative study 81/188 (43.1%); p < 0.0001(Chi2, 27.30). Of those admitted to hospital, 11/99 (11.1%) with positive ULDCT had surgery compared to 1/81 (1.2%) with a negative ULDCT; p < 0.008 (Chi2, 6.98). CONCLUSION: With its high clinical yield and similar radiation dose, ULDCT appears as a suitable alternative to abdominal radiography for the detection of select acute abdominal pathology in the emergency room.

CT Abdominal Tomography Indications: Are We All Sticking to the Plan?

OBJECTIVE: Ultra-low radiation dose computed tomography (CT) abdominal tomography was introduced in our institution in 2016 to replace standard abdominal radiography in the investigation of emergency department patients. This project aims to ascertain whether investigation of emergency department patients using ultra-low radiation dose CT abdominal tomography complies with original indication guidelines and/or if there has been any "indication creep" 3 years after inception. METHODS: Retrospective, quality assurance project with research ethics waiver. A review of 200 consecutive patients investigated with CT abdominal tomography between February and May 2017 was performed. This was compared with 200 consecutive patients investigated between February and May 2019. Data analyzed included patient demographics, indication for scan, as well as scan and patient outcomes. RESULTS: In the 2017 group, 29/200 scans were noncompliant with approved indication guidelines. In the 2019 group, 30/200 scans were also noncompliant. There was no statistically significant difference between groups (P < .05) regarding the use of approved indications. Forty of 200 scans performed in 2017 revealed additional findings which are not specifically addressed on the reporting template. Forty-one of 200 scans in 2019 revealed these findings. CONCLUSIONS: There has been no "indication creep" for CT abdominal tomography over time.

Frailty assessment prior to thoracic surgery for lung or esophageal cancer: a feasibility study.

BACKGROUND: Frailty assessment has not been thoroughly assessed in thoracic surgery. Our primary objective was to assess the feasibility of comprehensive frailty testing prior to lung and esophageal surgery for cancer. The secondary objective was to assess the utility of frailty indices in risk assessment prior to thoracic surgery. METHODS: Prospectively recruited patients completed multiple physiotherapy tests (6-min walk, gait speed, hand-grip strength), risk stratification (Charlson Comorbidity Index, Revised Cardiac Risk Index, Modified Frailty Index), and quality of life questionnaires. Lean psoas area was also assessed by a radiologist using positron emission tomography/computed tomography scans. Data was analyzed using Fisher's exact, Mann-Whitney U and independent t tests. RESULTS: The feasibility of comprehensive frailty assessment was assessed over a 4-month period among 40 patients (esophagus n = 20; lung n = 20). Risk stratification questionnaires administered in clinic had 100% completion rates. Physiotherapy testing required a trained physiotherapist and an additional visit to the pre-admission clinic; these tests proved difficult to coordinate and had lower completion rates (63-75%). Although most measures were not significantly associated with occurrence of complications, the Modified Frailty Index approached statistical significance (p = 0.06). CONCLUSIONS: Frailty assessment is feasible in the pre-operative outpatient setting and had a high degree of acceptance among surgeons and patients. Of the risk stratification questionnaires, the Modified Frailty Index may be useful in predicting outcomes as per this feasibility study. Pre-operative frailty assessment can identify vulnerable oncology patients to aid in treatment planning with the goal of optimizing clinical outcomes and resource allocation.

Prototype Ultrahigh-Resolution Computed Tomography for Chest Imaging: Initial Human Experience.

OBJECTIVE: The objective of this study was to evaluate a prototype, ultrahigh-resolution computed tomography offering higher reconstruction matrix (1024 × 1024) and spatial resolution (0.15 mm) for chest imaging. METHODS: Higher (1024) matrix reconstruction enabled by ultrahigh-resolution computed tomography scanner (128-detector rows; detector width, 0.25 mm; spatial resolution, 0.15 mm) was compared with conventional (512) reconstruction with image quality grading on a Likert scale (1, excellent; 5, nondiagnostic) for image noise, artifacts, contrast, small detail, lesion conspicuity, image sharpness, and diagnostic confidence. Image noise and signal-to-noise ratio were quantified. RESULTS: Diagnostic image quality was achieved for all scans on 101 patients. The 1024 reconstruction demonstrated increased image noise (20.2 ± 4.0 vs 17.2 ± 3.8, P < 0.001) and a worse noise rating (1.98 ± 0.63 vs 1.75 ± 0.61, P < 0.001) but performed significantly better than conventional 512 matrix with fewer artifacts (1.37 ± 0.43 vs 1.50 ± 0.48, P < 0.001), better contrast (1.50 ± 0.56 vs 1.62 ± 0.57, P < 0.001), small detail detection (1.06 ± 0.19 vs 2.02 ± 0.22, P < 0.001), lesion conspicuity (1.08 ± 0.23 vs 2.02 ± 0.24, P < 0.001), sharpness (1.09 ± 0.24 vs 2.02 ± 0.28, P < 0.001), and overall diagnostic confidence (1.09 ± 0.25 vs 1.18 ± 0.34, P < 0.001). CONCLUSIONS: Ultrahigh-resolution computed tomography enabled a higher reconstruction matrix and improved image quality compared with conventional matrix reconstruction, with a minor increase in noise.

Helical CT with variable target noise levels for dose reduction in chest, abdomen and pelvis CT.

OBJECTIVES: To evaluate a contiguous helical CT protocol with two different target noise levels in chest/abdomen/pelvis CT. METHODS: 41 patients (study group) underwent a helical scan (P1) with two different target noise levels (SDs), SD = 16 for chest and SD = 13 for abdomen/pelvis. Two further protocols were planned but not executed: a single helical scan with only one SD (SD = 13) for the entire scan range (P2), and two separate helical scans overlapping over the liver and same SD settings as for P1 (P3). All DLPs were recorded. Image quality was assessed qualitatively and quantitatively on all scans. The control group consisted of 40 patients, was scanned with protocol P3 and analysed using the same metrics. RESULTS: DLPs (mean/SD) for P1, P2 and P3 were 859.5/392.9, 1040.2/510.5 and 1027.4/469.4, respectively. P1 offered a mean dose reduction of 17.4% compared to P2, and 16.3% compared to P3 (both p < 0.001). There were no differences in image quality between both patient groups (p > 0.3). CONCLUSION: Contiguous helical scanning of the chest/abdomen/pelvis with variable target noise levels results in approximately 17% dose reduction if compared to a single acquisition with only abdominal dose settings or two separate acquisitions of the chest and abdomen/pelvis. KEY POINTS: • Low dose chest and standard abdomen CTs can be combined. • Variable SD CT scanning allows for radiation dose reduction. • Variable SD CT scanning maintains image quality.

Utility of transthoracic needle biopsy after lung transplantation.

The purpose of this study was to assess the diagnostic yield and complications of CT-guided transthoracic needle biopsy (TTNB) after lung transplantation. A database search identified all TTNB performed in lung transplant patients over a 14-year period. Forty-two biopsies in transplant patients (transplant group) were identified and matched to the next biopsy performed in native lungs by the same operator (nontransplant group) as a control. Primary outcomes recorded were diagnosis, diagnostic yield, pneumothorax requiring intervention, and symptomatic pulmonary hemorrhage. Biopsy outcomes were classified as diagnostic, not specifically diagnostic, and nondiagnostic. Patients in the transplant group were younger (P < .002). Emphysema along the biopsy trajectory was more commonly seen in the nontransplant group (P < .0006). Needle gauge, size of lesion, pleural punctures, lesion depth, and number of passes were not significantly different. Diagnostic yield was 71% in the transplant group and 91% in the nontransplant group. There were 20 of 42 (48%) malignant nodules in the transplant group compared to 31 of 44 (70%) nodules in the nontransplant group (P = .05). There were no complications in the transplant group. The nontransplant group had two pneumothoraces requiring intervention. TTNB after lung transplant is safe with a moderate diagnostic yield. Nonmalignant lesions are more common after lung transplantation.

Changes of Emphysema Parameters over the Respiratory Cycle During Free Breathing: Preliminary Results Using Respiratory Gated 4D-CT.

The purpose of this research was to evaluate respiratory gated CT of the lung in patients with COPD for analysis of parenchymal characteristics who were potential candidates for volume reduction surgery. Eleven patients with clinically known emphysematous disease underwent a respiratory gated, free-breathing 64-multislice-CT (Aquilion 64, Toshiba). Retrospective image reconstruction was performed similar to cardiac CT at every 10% of the respiratory loop, resulting in 10 complete volumetric datasets at 10 equidistant time points. All images were transferred onto a PC for calculation of the total lung volume, emphysema volume, emphysema index, and mean lung density. Complete datasets could be successfully reconstructed in all patients. The mean lung volume increased from 6.9 L to 7.5 L over the respiratory cycle. Emphysema volume increased from 1.6 L to 2.0 L and emphysema index from 22.6% to 26.5% from expiration to inspiration. In conclusion, respiratory gated chest 4D-CT allows for combined morphologic and functional image analysis, which can provide new insight into functional impairment and individual treatment planning.

A phase II trial of second-line axitinib following prior antiangiogenic therapy in advanced hepatocellular carcinoma.

BACKGROUND: Second-line treatment options in advanced hepatocellular carcinoma (HCC) are limited. Axitinib, a selective potent tyrosine kinase inhibitor (TKI) of vascular endothelial growth factor VEGF) receptors 1, 2, and 3, merits exploration in HCC. METHODS: This was a single-arm phase II trial of axitinib in advanced HCC. Eligible patients were Child-Pugh A/B7, with measurable progressive disease after TKIs/antiangiogenic drugs. Axitinib was started at 5 mg twice daily orally, titrated from 2 to 10 mg twice daily as tolerated. The primary end point was tumor control at 16 weeks by RECIST1.1; secondary end points were response rate, comparing response by RECIST1.1 to Choi and modified RECIST, exploring dynamic contrast-enhanced imaging models, safety, progression-free (PFS), and overall survival (OS). RESULTS: Thirty patients were treated. Of 26 patients evaluable for response, there were 3 partial responses (PR) per RECIST1.1; 13 PR by Choi, 6 PR and 1 complete response by modified RECIST. Tumor control rate at 16 weeks was 42.3%. Two-week perfusion changes were noted on functional imaging. Of 21 patients with evaluable α-fetoprotein response, 43% had >50% decrease from baseline. Most common axitinib-related grade 3/4 adverse events (AEs) were hypertension, thrombocytopenia and diarrhea. Of 11 patients with any grade hypertension, 7 had disease control >36 wks. Four patients discontinued treatment due to AEs. Median PFS was 3.6 months. Median OS was 7.1 months. CONCLUSIONS: With 42.3% tumor control at 16 weeks, primary endpoint was met. Axitinib has shown encouraging tolerable clinical activity in VEGF-pretreated HCC patients but further study should be in a selected population incorporating potential biomarkers of response.

Increase in Utilization of Afterhours Medical Imaging: A Study of Three Canadian Academic Centers.

OBJECTIVES: The objectives of our study were to assess trends in afterhours medical imaging utilization for emergency department (ED) and inpatient (IP) patient populations from 2006-2013, including analysis by modality and specialty and with adjustment for patient volume. METHODS: For this retrospective study, we reviewed the number of CT, MRI, and ultrasound studies performed for the ED and IP patients during the afterhours time period (5pm - 8am on weekdays and 24 hours on weekends and statutory holidays) from 2006-2013 at three different Canadian academic hospitals. We used the Jonckheere-Terpstra (JT) test to determine statistical significance of imaging and patient volume trends. A regression model was used to examine whether there was an increasing trend over time in the volume of imaging tests per 1000 patients. RESULTS: For all three sites from 2006-2013 during the afterhours time period: There was a statistically significant increasing trend in total medical imaging volume, which also held true when the volumes were assessed by modality and by specialty. There was a statistically significant increasing trend in ED and IP patient volume. When medical imaging volumes were adjusted for patient volumes, there was a statistically significant increasing trend in imaging being performed per patient. CONCLUSION: Afterhours medical imaging volumes demonstrated a statistically significant increasing trend at all three sites from 2006-2013 when assessed by total volume, modality, and specialty. During the same time period and at all three sites, the ED and IP patient volumes also demonstrated a statistically significant increasing trend with more medical imaging, however, being performed per patient.

How influential is the duration of contrast material bolus injection in perfusion CT? evaluation in a swine model.

PURPOSE: To analyze the effect of the duration of contrast material bolus injection on perfusion values in a swine model by using the maximum slope method. MATERIALS AND METHODS: This study was approved by the institutional animal care committee. Twenty pigs (weight range, 63-77 kg) underwent dynamic volume computed tomography (CT) of the kidneys during suspended respiration. Before the CT examination, a miniature cuff-shaped ultrasonographic flow probe encircling the right renal artery was surgically implanted in each pig to obtain true perfusion values. Two sequential perfusion CT series were performed in 30 seconds, each comprising 30 volumes with identical parameters (100 kV, 200 mAs, 0.5 sec rotation time). The duration of contrast material bolus (0.5 mL/kg of body weight) was 3.8 seconds in the first series (short bolus series) and 11.5 seconds in the second series (long bolus series), and the injection flow rate was adapted accordingly. In each pig, cortical kidney volume was determined by using the volume with the highest cortical enhancement. CT perfusion values were calculated for both series by using the maximum slope method and were statistically compared and correlated with the true perfusion values from the flow probe by using linear regression analysis. RESULTS: Mean true perfusion and CT perfusion values (in minutes(-1)) for the short bolus series were 1.95 and 2.03, respectively (P = .22), and for the long bolus series, they were 2.02 and 1.92, respectively (P = .12). CT perfusion showed very good correlation with true perfusion in both the short (slope, 1.01; 95% confidence interval: 0.91, 1.11) and long (slope, 0.92; 95% confidence interval: 0.78, 1.04) series. On the basis of the regression analysis, CT perfusion values in the short bolus series were overestimated by 1% and those in the long bolus series were underestimated by 8%. CONCLUSION: Duration of contrast material bolus injection does not influence CT perfusion values substantially. The longer, clinically preferred intravenous injection scheme is sufficiently accurate for CT perfusion.

Hybrid iterative reconstruction technique for abdominal CT protocols in obese patients: assessment of image quality, radiation dose, and low-contrast detectability in a phantom.

OBJECTIVE: The purpose of this study was to assess the impact of a noise reduction technique on image quality, radiation dose, and low-contrast detectability in abdominal CT for obese patients. MATERIALS AND METHODS: A liver phantom with 12 different tumors was designed, and fat rings were added to mimic intermediately sized and large patients. The intermediate and large phantoms were scanned with our standard abdominal CT protocol (image noise level of 15 HU and filtered back projection [FBP]). The large phantom was scanned with five different noise levels (10, 12.5, 15, 17.5, and 20 HU). All datasets for the large phantom were reconstructed with FBP and the noise reduction technique. The image noise and the contrast-to-noise ratio (CNR) were assessed. Tumor detection was independently performed by three radiologists in a blinded fashion. RESULTS: The application of the noise reduction method to the large phantom decreased the measured image noise (range, -14.5% to -37.0%) and increased the CNR (range, 26.7-70.6%) compared with FBP at the same noise level (p < 0.001). However, noise reduction was unable to improve the sensitivity for tumor detection in the large phantom compared with FBP at the same noise level (p > 0.05). Applying a noise level of 15 HU, the overall sensitivity for tumor detection in the intermediate and large phantoms with FBP measured 75.5% and 87.7% and the radiation doses measured 42.0 and 23.7 mGy, respectively. CONCLUSION: Although noise reduction significantly improved the quantitative image quality in simulated large patients undergoing abdominal CT compared with FBP, no improvement was observed for low-contrast detectability.

Iterative reconstruction algorithm for CT: can radiation dose be decreased while low-contrast detectability is preserved?

PURPOSE: To compare the low-contrast detectability and image quality of computed tomography (CT) at different radiation dose levels reconstructed with iterative reconstruction (IR) and filtered back projection (FBP). MATERIALS AND METHODS: A custom liver phantom with 12 simulated hypoattenuating tumors (diameters of 5, 10, 15, and 20 mm; tumor-to-liver contrast values of -10, -20, and -40 HU) was designed. The phantom was scanned with a standard abdominal CT protocol with a volume CT dose index of 21.6 mGy (equivalent 100% dose) and four low-dose protocols (20%, 40%, 60%, and 80% of the standard protocol dose). CT data sets were reconstructed with IR and FBP. Image noise was measured, and the tumors' contrast-to-noise ratios (CNRs) were calculated. Tumor detection was independently assessed by three radiologists who were blinded to the CT technique used. A total of 840 simulated tumors were presented to the radiologists. Statistical analyses included analysis of variance. RESULTS: IR yielded an image noise reduction of 43.9%-63.9% and a CNR increase of 74.1%-180% compared with FBP at the same dose level (P < .001). The overall sensitivity for tumor detection was 64.7%-85.3% for IR and 66.3%-85.7% for FBP at the 20%-100% doses, respectively. There was no significant difference in the sensitivity for tumor detection between IR and FBP at the same dose level (P = .99). The sensitivity of the protocol at the 20% dose with FBP and IR was significantly lower than that of the protocol at the 100% dose with FBP and IR (P = .019). CONCLUSION: As the radiation dose at CT decreases, the IR algorithm does not preserve the low-contrast detectability. SUPPLEMENTAL MATERIAL: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13122349/-/DC1.