Frank Dong

Contrast-to-Noise Ratio and Low-Contrast Object Resolution on Full- and Low-Dose MDCT: SAFIRE Versus Filtered Back Projection in a Low-Contrast Object Phantom and in the Liver

OBJECTIVE The purpose of this article is to evaluate the effect of sinogram-affirmed iterative reconstruction (SAFIRE) on contrast-to-noise ratio (CNR) compared with filtered back projection (FBP) and to determine whether SAFIRE improves low-contrast object detection or conspicuity in a low-contrast object phantom and in the liver on full- and low-dose examinations. SUBJECTS AND METHODS A low-contrast object phantom was scanned at 100%, 70%, 50%, and 30% dose using a single-source made of a dual-source MDCT scanner, with the raw data reconstructed with SAFIRE and FBP. Unenhanced liver CT scans in 22 patients were performed using a dual-source MDCT. The raw data from both tubes (100% dose) were reconstructed using FBP, and data from one tube (50% dose) were reconstructed using both FBP and SAFIRE. CNR was measured in the phantom and in the liver. Noise, contrast, and CNR were compared using paired Student t tests. Six readers assessed sphere detection and conspicuity in the phantom and liver-inferior vena cava conspicuity in the patient data. The phantom and patient data were assessed using multiple-variable logistic regression. RESULTS The phantom at 70% and 50% doses with SAFIRE had decreased noise and increased CNR compared with the 100% dose with FBP. In the liver, the mean CNR improvement at 50% dose with SAFIRE compared with FBP was 31.4% and 88% at 100% and 50% doses, respectively (p < 0.001). Sphere object detection and conspicuity improved with SAFIRE (p < 0.001). However, smaller spheres were obscured on both FBP and SAFIRE images at lower doses. Liver-vessel conspicuity improved with SAFIRE over 50%-dose FBP in 67.4% of cases (p < 0.001), and versus 100%-dose FBP, improved in 38.6% of cases (p = 0.085). As a predictor for detection, CNR alone had a discriminatory ability (c-index, 0.970) similar to that of the model that analyzed dose, lesion size, attenuation difference, and reconstruction technique (c-index, 0.978). CONCLUSION Lower dose scans reconstructed with SAFIRE have a higher CNR. The ability of SAFIRE to improve low-contrast object detection and conspicuity depends on the radiation dose level. At low radiation doses, low-contrast objects are invisible, regardless of reconstruction technique.

Optimization of kVp and mAs for pediatric low-dose simulated abdominal CT: is it best to base parameter selection on object circumference?

OBJECTIVE The objective of our study was to determine the effect of mAs and kVp reduction on pediatric phantoms based on patient circumference to optimize dose reduction and maintain image quality for abdominal CT. SUBJECTS AND METHODS Three polymethylmethacrylate right cylindric CT dose index (CTDI) phantoms with diameters of 10, 16, and 32 cm simulated the abdomen of an infant, child, and adolescent, respectively. Using a National Institute of Standards & Technology ion chamber and Victoreen 660 electrometer, doses at centerline were recorded on a 16-MDCT scanner. Measurements were obtained in incremental steps from 50 to 400 mAs and from 80 to 140 kVp. Noise was calibrated to clinical images through a calibration factor. RESULTS For phantoms of all circumferences, doses increased linearly with an increase in mAs and by the power function of kVp(n) for increases in kVp. There was an associated decrease in noise for all circumferences and a sharp decrease at lower doses with a plateau at higher doses. Using a noise threshold of 20 HU and a dose threshold of 2.5 cGy, a range of imaging parameters was established for each circumference from which technique optimization curves were created to determine optimal mAs and kVp pairs. The mean measured dose was 2.435 ± 0.019 cGy. The mean measured noise was 29.35 ± 1.45 HU. CONCLUSION For pediatric CT, the most accurate way to strike the balance between image quality and radiation dose is to adjust dose to abdominal circumference, not body weight or age. Our data support the use of technique optimization curves to optimize kVp and mAs.

Effect of Reduced Radiation Exposure and Iterative Reconstruction on Detection of Low-Contrast Low-Attenuation Lesions in an Anthropomorphic Liver Phantom: An 18-Reader Study

PURPOSE To measure the effect of reduced radiation exposure on low-contrast low-attenuation liver lesion detection in an anthropomorphic abdominal phantom by using filtered back projection (FBP) and sinogram-affirmed iterative reconstruction. MATERIALS AND METHODS Eighteen radiologists blinded to phantom and study design interpreted randomized image data sets that contained 36 spherical simulated liver lesions of three sizes and three attenuation differences (5-mm diameter: 12, 18, and 24 HU less than the 90-HU background attenuation of the simulated liver insert; 10- and 15-mm diameter: 6, 12, and 18 HU less than the 90-HU background attenuation) scanned with four discrete exposure settings and reconstructed by using FBP and sinogram-affirmed iterative reconstruction. Response assessment included region-level lesion presence or absence on a five-point diagnostic confidence scale. Statistical evaluation included multireader multicase receiver operating characteristic curve analysis, with nonparametric methods and noninferiority analysis at a margin of -0.10. RESULTS Pooled accuracy at 75% exposure for both FBP and sinogram-affirmed iterative reconstruction was noninferior to 100% exposure (P = .002 and P < .001, respectively). Subsequent exposure reductions resulted in a significant decrease in accuracy. When the smallest (5-mm-diameter) lesions were excluded from analysis, sinogram-affirmed iterative reconstruction was superior to FBP at 100% exposure (P = .011), and sinogram-affirmed iterative reconstruction at 25% and 50% exposure reduction was noninferior to FBP at 100% exposure (P ≤ .013). Reader confidence was greater with sinogram-affirmed iterative reconstruction than with FBP for 10- and 15-mm lesions (2.94 vs 2.76 and 3.62 vs 3.52, respectively). CONCLUSION In this low-contrast low-attenuation liver lesion model, a 25% exposure reduction maintained noninferior diagnostic accuracy. However, detection was inferior with each subsequent exposure reduction, regardless of reconstruction method. Sinogram-affirmed iterative reconstruction and FBP performed equally well at modest exposure reduction (25%-50%). Readers had higher confidence levels with sinogram-affirmed iterative reconstruction for the 10- and 15-mm lesions.

Detection of Urolithiasis: Comparison of 100% Tube Exposure Images Reconstructed with Filtered Back Projection and 50% Tube Exposure Images Reconstructed with Sinogram-affirmed Iterative Reconstruction

PURPOSE To compare images acquired with 50% tube exposure with a dual-source computed tomographic (CT) scanner and reconstructed with sinogram-affirmed iterative reconstruction (SAFIRE) with 100% exposure images reconstructed with filtered back projection (FBP) for reader ability to detect stones, reader confidence, and findings outside the urinary tract. MATERIALS AND METHODS In this HIPAA-compliant, institutional review board-approved study, imaging examinations in 99 patients with urolithiasis were assessed. Data from both tubes were reconstructed with FBP; data from the primary tube only were reconstructed with SAFIRE. Seven readers evaluated randomized studies for calculi in nine regions. Reader confidence was scored by using a five-point scale. Ancillary findings were noted. Nonparametric methods for clustered data were used to estimate the area under the receiver operating characteristic curves with 95% confidence intervals to test for noninferiority of 50% exposure with SAFIRE. RESULTS Calculi were found in 113 locations (pyelocalyceal ureter, 86; proximal ureter, seven; midureter, four; distal ureter, 15; bladder, one) and not found in 752 locations. Mean area under the receiver operating characteristic curve for FBP was 0.879 (range, 0.607-0.967) and for SAFIRE, 0.883 (range, 0.646-0.971; 95% confidence interval: -0.025, 0.031). The SAFIRE images were not significantly inferior to FBP images (P = .001). Reader confidence levels for images with stones were similar with FBP and SAFIRE (P = .963). For the 52 patients who had extraurinary findings, readers reported them correctly in 74.4% (271 of 364) and 72.0% (262 of 364) of cases (P = .215) for FBP and SAFIRE, respectively. For the nine patients with potentially important findings per the reference standard, the detection rates were 44% (28 of 63) and 33% (21 of 63, P = .024), respectively. For the 43 patients with unimportant or likely unimportant findings, the false detection rates were 15% (44 of 301) and 14% (43 of 301, P = .756), respectively. CONCLUSION The 50% tube exposure CT images reconstructed with SAFIRE were not inferior to 100% exposure images reconstructed with FBP for diagnosis of urolithiasis, without decreases in reader confidence.

Optimization of Kilovoltage and Tube Current–Exposure Time Product Based on Abdominal Circumference: An Oval Phantom Study for Pediatric Abdominal CT

OBJECTIVE This CT study evaluates image noise and radiation dose using a modified CT dose index phantom to approximate pediatric abdominal shape. Contrast-to-noise ratio (CNR) and radiation dose were measured. MATERIALS AND METHODS The oval shape was simulated by fixing 1000-mL saline bags aside cylindric phantoms with variable circumferences. The doses at the center and peripheral holes in the phantom were recorded. Measurements were obtained at 50-400 mAs and 80-140 kVp. Diluted iodine contrast agent filled the center hole, and distilled water filled the peripheral holes. CNR was defined as the difference in CT number between diluted iodine and water divided by the standard deviation (SD) of CT number of water. RESULTS Dose increased linearly with increases in tube current-exposure time product and by a power function (proportional to kVp(n), where n = 2.64-3.09) for increases in kilovoltage. A range of scanning parameters was established for each circumference from which technique optimization curves were created to determine the best tube current-time product and kilovoltage pairs when noise was less than 20 HU and dose was less than 2.5 cGy. CNR increased by 40% as kilovoltage was reduced from 140 to 80 kVp. A dose reduction of 70% was observed for 140 versus 80 kVp for the same CNR. CONCLUSION Because pediatric patients of the same age and weight come in all shapes and sizes, abdominal circumference is a useful clinical parameter on which to base CT scan techniques controlling radiation output--namely kilovoltage and tube current-time product. Low-kilovoltage techniques for patients with small circumference show better iodine CNR.

Estimated radiation exposure and cancer risk from CT and PET/CT scans in patients with lymphoma

INTRODUCTION The purpose of this study was to estimate total effective dose and cancer risk related to treatment monitoring and surveillance computed tomography (CT) scans in a cohort of patients diagnosed with lymphoma. METHODS 76 patients with head, neck, chest, abdomen or pelvis CT and whole-body positron emission tomography (PET)/CT were identified from an institutional lymphoma database; this included 54 (71%) patients with non-Hodgkin and 22 (29%) patients with classical Hodgkin lymphoma. Average treatment and surveillance periods were 8 months (range, 3-14 mo) and 23 months (range, 1-40 mo), respectively. Radiation exposure was estimated from the dose-length product (DLP) for CT scans and milli-Curies and DLP for PET/CT scans. Cancer risk was estimated using the Biological Effects of Ionizing Radiation model. RESULTS During their treatment period, 45 patients had 161 CT exams and 39 patients had 73 PET/CT exams. Mean effective dose was 39.3 mSv (range, 7.1-100 mSv). During the surveillance period, 60 patients had 378 CT exams and 25 patients had 39 PET/CT exams. Mean effective dose was 53.2 mSv (range, 2.6-154 mSv). Seventeen of 76 (22.4%) patients had total cumulative doses greater than 100 mSv. The mean increase in estimated cancer risk was 0.40%; the greatest estimated risk to any one patient was 1.19%. CONCLUSION Mean total effective dose and mean estimated cancer risk were low in patients with lymphoma undergoing serial imaging, suggesting that theoretical risks of radiation-induced cancer need not be a major consideration in radiologic follow-up.

Dose Reduction for Abdominal and Pelvic MDCT After Change to Graduated Weight-Based Protocol for Selecting Quality Reference Tube Current, Peak Kilovoltage, and Slice Collimation

OBJECTIVE The purpose of this article is to determine the decrease in volume CT dose index (CTDI(vol)) and dose-length product (DLP) achieved by switching from fixed quality reference tube current protocols with automatic tube current modulation to protocols adjusting the quality reference tube current, slice collimation, and peak kilovoltage according to patient weight. MATERIALS AND METHODS All adult patients who underwent CT examinations of the abdomen or abdomen and pelvis during 2010 using weight-based protocols who also underwent a CT examination in 2008 or 2009 using fixed quality reference tube current protocols were identified from the radiology information system. Protocol pages were electronically retrieved, and the CT model, examination date, scan protocol, CTDI(vol), and DLP were extracted from the DICOM header or by optical character recognition. There were 15,779 scans with dose records for 2700 patients. Changes in CTDI(vol) and DLP were compared only between examinations of the same patient and same CT system model for examinations performed in 2008 or 2009 and those performed in 2010. The final analysis consisted of 1117 comparisons in 1057 patients, and 1209 comparisons in 988 patients for CTDI(vol) and DLP, respectively. RESULTS The change to a weight-based protocol resulted in a statistically significant reduction in CTDI(vol) and DLP on three MDCT system models (p < 0.001). The largest average CTDI(vol) decrease was 13.9%, and the largest average DLP decrease was 16.1% on a 64-MDCT system. Both the CTDI(vol) and DLP decreased the most for patients who weighed less than 250 lb (112.5 kg). CONCLUSION Adjusting the CT protocol by selecting parameters according to patient weight is a viable method for reducing CT radiation dose. The largest reductions occurred in the patients weighing less than 250 lb.

CT Radiation Dose Optimization and Tracking Program at a Large Quaternary-Care Health Care System

PURPOSE The authors report the implementation and outcomes of a CT radiation dose optimization and tracking program at a large quaternary-care health care system. METHODS A committee reviewed, optimized, and released standardized imaging protocols for the most common CT examinations across the health system. Volume CT dose index and dose-length product (DLP) diagnostic reference levels (DRLs) were established, with the goal of decreasing the percentage of outliers (CT scans with DLPs greater than the established DRLs) to <5% of tracked CT examinations. Baseline radiation dose data were manually extracted for 5% of total examinations. A semiautomated process to analyze all DLP data was then implemented to monitor outliers. RESULTS The baseline percentage of outliers was slightly higher than 10% for pediatric scans but nearly 26.5% for adult scans. Over the first year, after standardized protocols were distributed, the percentage of outliers decreased for pediatric brain (from 22% to 6%), adult brain (from 23% to 3%), and adult chest (from 22% to 11%) examinations. Over the next 2 years, after the dose-tracking program was implemented, the percentage of outliers decreased for adult (brain, from 3% to 1%; chest, from 11% to 1%; abdomen, from 24% to 1%) and pediatric (brain, from 6% to 2%; chest, from 11% to 0%; abdomen, from 7% to 1%) examinations. CONCLUSIONS The reported CT protocol optimization and dose-tracking program enabled a sustainable reduction in the proportion of CT examinations being performed above established DRLs from as high as 26% to <1% over a period of 2 years.

Bundling of Abdomen/Pelvis CT Codes and Change in Ionizing Radiation Exposure

Bundling of Abdomen/Pelvis CT Codes and Change in Ionizing Radiation Exposure We read with interest the article by Rayo et al in the July 2014 issue of JACR [1]. The authors note a 15% net decrease in the total volume of annual CT procedures from 2008 to 2012 in the inpatient population at their urban, tertiary-care hospital. This decrease was purportedly driven primarily by the 37% decrease in abdominal/pelvic CT imaging volume, which was, however, not associated with a meaningful abdominal ultrasound volume increase. PerTable 1 in the article, the absolute volume of abdominal/pelvic CT procedures steadily increased from 2008 through 2010, before declining precipitously through 2011-2012. In comparison, volumes for head, sinus, and lumbar spine CT fluctuated slightly from yearto-year but remained relatively unchanged after the5-year period.Rayo et al hypothesize that advanced abdominal imaging volume, in general, decreased in their inpatient population. They also suggest that a decreasing imaging rate may indicate increasingly conservative prescribing behavior on the part of referring physicians and radiologists. One possibility, perhaps even a likely possibility, is that the observed decrease in abdominal/pelvic CT volume, which is markedly disproportionate when compared to other body regions, is at least in part due to a change in coding procedure that the authors did not discuss and thereforemay have overlooked. TheCPT codes used by the authors to retrieve information about the abdominal/pelvic CTswere: 72192, 72193, 72194, 74150, 74160, 74170, 74176, 74177, and 74178. However, the codes for abdominal CT and pelvic CT were bundled together startingon January1,2011 [2,3]. As a result, CT of the abdomen and pelvis

Radiation Exposure in the Medical ICU: Predictors and Characteristics

Background Patients admitted to the medical ICU (MICU) are often subjected to multiple radiologic studies. We hypothesized that some endure radiation dose exposure (cumulative effective dose [CED]) in excess of annual US federal occupational health standard limits (CED ≥ 50 mSv) and 5‐year cumulative limit (CED ≥ 100 mSv). We also evaluated the correlation of CED with Acute Physiology and Chronic Health Evaluation (APACHE) III score and other clinical variables. Methods Retrospective observational study conducted in an academic medical center involving all adult admissions (N = 4,155) to the MICU between January 2013 and December 2013. Radiation doses from ionizing radiologic studies were calculated from reference values to determine the CED. Results Three percent of admissions (n = 131) accrued CED ≥ 50 mSv (1% [n = 47] accrued CED ≥ 100 mSv). The median CED was 0.72 mSv (interquartile range, 0.02‐5.23 mSv), with a range of 0.00 to 323 mSv. Higher APACHE III scores (P = .003), longer length of MICU stay (P < .0001), sepsis (P = .03), and gastrointestinal disorders and bleeding (P < .0001) predicted higher CED in a multivariable linear regression model. Patients with gastrointestinal bleeding and disorders had an odds ratio of 21.05 (95% CI, 13.54‐32.72; P < .0001) and 6.94 (95% CI, 3.88‐12.38; P < .0001), respectively, of accruing CED ≥ 50 mSv in a multivariable logistic regression model. CT scan and interventional radiology accounted for 49% and 38% of the total CED, respectively. Conclusions Patients in the MICU are exposed to radiation doses that can be substantial, exceeding federal annual occupational limits, and in a select subset, are > 100 mSv. Efforts to justify, restrict, and optimize the use of radiologic resources when feasible are warranted.