Andrew N Primak

Mayo Foundation for Medical Education and Research, Scottsdale, AZ, United States

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Publications (85)163.24 Total impact

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    ABSTRACT: To compare radiation dose surrogates [volume CT dose index (CTDIvol), dose-length product (DLP), size-specific dose estimate (SSDE), and effective dose] and image noise in a cohort of patients undergoing hepatocellular carcinoma screening who underwent both single-energy CT (SECT) and dual-energy CT (DECT).
    Clinical radiology. 10/2014;
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    ABSTRACT: Iterative metal artifact reduction (IMAR) is a sinogram inpainting technique that incorporates high-frequency data from standard weighted filtered back projection (WFBP) reconstructions to reduce metal artifact on computed tomography (CT). This study was designed to compare the image quality of IMAR and WFBP in total shoulder arthroplasties (TSA); determine the optimal amount of WFBP high-frequency data needed for IMAR; and compare image quality of the standard 3D technique with that of a faster 2D technique.
    Skeletal Radiology 08/2014; · 1.74 Impact Factor
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    ABSTRACT: 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. © RSNA, 2014.
    Radiology 05/2014; · 6.34 Impact Factor
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    ABSTRACT: 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. © RSNA, 2014 Online supplemental material is available for this article.
    Radiology 03/2014; · 6.34 Impact Factor
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    ABSTRACT: PURPOSE Iterative metal artifact reduction (IMAR) is a new sinogram inpainting technique to reduce CT metal artifact which adds high frequency data to improve visualization close to metal edges. Our purpose was to compare the image quality and accuracy of attenuation values near hardware of IMAR and standard filtered back projection (FBP) in patients with shoulder arthroplasties (SA). METHOD AND MATERIALS 8 patients (6 male, avg age 60) with 9 SAs were scanned on a FLASH CT (Siemens) with a standard protocol (140 kVp, 300 eff mAs, 0.6mm collimation, eff pitch 0.35-0.8). Images were reconstructed on a standalone workstation with a smooth kernel (B30) and 0.6mm slice thickness. 3 IMAR reconstructions with different amounts of high frequency data: IMAR (least), IMAR1.5 (more), IMAR2.5 (most) and FBP were ranked for image quality by 5 readers in a side by side comparison from best=1 to worst=4 for bone, soft tissue, metal-bone interface and overall quality. Accuracy of attenuation near hardware was quantified as the absolute difference (AD) between avg HU within a region of interest (ROI) near hardware and for an ROI containing similar tissues on a slice without hardware. RESULTS IMAR1.5 was ranked best for humeral cortex (avg 1.4), glenoid trabeculae (avg 1.36) and glenoid cortex (avg 1.4). IMAR2.5 was ranked best for humeral trabeculae (avg 1.2). IMAR was ranked the best for deltoid muscle (avg 1.2). IMAR1.5 and 2.5 were ranked best for metal-bone interface (avg 1.3). FBP was ranked worst for all structures (avg 3.38 -3.49). All readers ranked IMAR1.5 and 2.5 over FBP (p<0.05) for overall image quality. 3 readers preferred IMAR1.5 and 2.5 over IMAR (p<0.05). There were no significant differences between IMAR1.5 and 2.5 for any reader. Accuracy of attenuation near hardware was significantly better in all 3 IMAR reconstructions than FBP for bone (AD 86–99 vs 430, p<0.006) and soft tissue (AD 23–29 vs 450, p=0.003). There was no significant difference between the IMAR techniques in bone (p=0.4) or soft tissue (p=0.4). CONCLUSION IMAR, especially with added high frequency data, had superior image quality and more accurate attenuation values near hardware than standard FBP in patients with shoulder arthroplasties. CLINICAL RELEVANCE/APPLICATION IMAR is a promising new CT technique to reduce metal artifact that is fully automatic and computationally inexpensive and has the potential to replace standard FBP in patients with hardware.
    Radiological Society of North America 2013 Scientific Assembly and Annual Meeting; 12/2013
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    ABSTRACT: PURPOSE To compare the dose and noise level between single energy (SE) and dual energy (DE) multi-detector computed tomography (MDCT) examinations in patients undergoing screening for Hepatocellular Carcinoma (HCC). METHOD AND MATERIALS IRB-approved, HIPPA-compliant prospective study of 59 adult subjects (mean age 59.5yrs) undergoing HCC screening with 3-phase CT (unenhanced, arterial and portal-venous phases), who were each examined on both SE (Sensation 64, Siemens Healthcare) and DE CT scanners (Flash, Siemens Healthcare) on different dates. SE scans were performed using 120kVp and weight-based mAs (mAs=patient’s weight), and DE scans at 100kVP and 140kVp, with mAs adjusted to match the estimated CTDIvol of a weight-based mAs SE scan. The CTDIvol and DLP of each phase were recorded. Maximum anteroposterior and transverse dimensions measured from CT radiographs were used to calculate the effective diameter (ED) and size-specific dose estimate (SSDE). Regions of interest (ROI) were drawn in liver, retroperitoneal (RP) fat, IVC, and aorta and Hounsfield unit values with Standard Deviation (SD) recorded. Paired t-tests were used to compare BMI, weight, and ED at the time of the two imaging studies. Distributions of outcome variables (dose and noise) were examined using Q-Q plots and Shapiro tests. RESULTS BMI and weight of the subjects were highly correlated with the ED (r=0.75 and 0.87) and did not differ significantly between the two scans. CTDIvol and SSDE were significantly lower for all the phases on DE scans compared to SE scans (p-values<0.001 for all the comparisons). On the DE scans, the mean CTDIvol and SSDE were 8.6 and 8.2mGy, respectively, for each unenhanced and arterial phase, and 8.8 and 8.5mGy for the portal venous phase. On the SE scans, the mean CTDIvol and SSDE were 12.6 and 12.7 mGy for each unenhanced and arterial phase, and 13.5 and 13.7mGy for the portal venous phase The mean noise was not significantly different for DE and SE scans for both the liver and RP fat (p-values 1.0), but was significantly lower for the DE than the SE scan for the IVC (22 vs. 23.2; p=0.025) and aorta (25.2 vs. 26.2;p=0.008). CONCLUSION Dose with the MDCT DE scanning protocol was significantly lower when compared to SE examinations, with either similar or lower noise levels. CLINICAL RELEVANCE/APPLICATION DE scanning protocols can be an alternative to decrease dose in patients undergoing HCC screening who require repetitive imaging.
    Radiological Society of North America 2013 Scientific Assembly and Annual Meeting; 12/2013
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    ABSTRACT: PURPOSE To assess the effect of reduced radiation exposure and reconstruction method on detection of lesions that are low-contrast, low-attenuation (LCLA) relative to the background liver METHOD AND MATERIALS Semi-anthropomorphic phantom containing custom inserts with 36 spherical liver lesions of 3 sizes and attenuations (10 and 15-mm at 6, 12 and 18HU, and 5-mm at 12, 18 and 24HU below 90HU simulated liver) was scanned at 120kVp, 0.6-mm collimation, 200 (CTDIvol 13.49), 150, 100 and 50mAs on a 128-slice MDCT scanner (Definition Flash, Siemens). Lesions were distributed non-uniformly to reduce memory bias. Images were reconstructed at 3-mm thickness using filtered back projection (FBP) and sinogram-affirmed iterative reconstruction (SAFIRE, S3). A randomized dataset containing 256-images was generated for each reader (12 images with one lesion, 12 with two lesions and 8 without lesions, for each dose and reconstruction method). Eighteen Radiologists blinded to phantom and study design independently reported region-level lesion presence or absence on a 5-point diagnostic confidence scale. Statistical evaluation included multi-reader, multi-case (MRMC) ROC analysis using nonparametric methods with the area under the ROC curve (AUC) considered accuracy. RESULTS Pooled AUC decreased with each 25% reduction from 100% dose: 0.848, 0.842, 0.792 and 0.743 for FBP; and 0.862, 0.855, 0.785 and 0.735 for SAFIRE. At a given dose, improvement in AUC with SAFIRE was, however, not statistically significant. For both FBP and SAFIRE, accuracy at 75% dose was statistically equivalent to 100% dose FBP (p =0.002 and <0.001 respectively). When lesions with the lowest attenuation difference (6HU) were excluded, AUC at 50% SAFIRE (0.800) was not statistically equivalent to 100% FBP (0.846) (p=0.1) although AUC at 50% FBP (0.809) was found equivalent (p=0.029). CONCLUSION In this LCLA liver lesion model, a 25% dose reduction did not reduce detection of the lesions studied. However, detection was inferior with each subsequent dose reduction regardless of reconstruction method. For lesions with attenuation differences larger than or equal to 12HU, lesion detection was not reduced even at 50% dose with FBP. CLINICAL RELEVANCE/APPLICATION Estimates of loss of accuracy at reduced doses and limits of iterative reconstruction should be known especially for low contrast, low attenuation liver lesions to enable dose optimization in practice
    Radiological Society of North America 2013 Scientific Assembly and Annual Meeting; 12/2013
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    ABSTRACT: PURPOSE To assess the effect of CT dose reduction on the detection of urolithiasis. METHOD AND MATERIALS 99 patients with 192 kidneys (6 solitary) were imaged to follow urolithiasis on a dual energy scanner [Definition Flash (Siemens Healthcare)] in dual-source mode using 120 kVp, 128x0.6 collimation & pitch 0.9. Dose modulation used with weight-based reference mAs. Data from both tubes was reconstructed with standard filtered back projection (100% FBP). Data from primary tube (50% total dose) was reconstructed using sonogram-affirmed iterative reconstruction i31 (50% IR). 7 readers (2 senior & 2 junior staff, 2 imaging fellows, 1 urology fellow) evaluated 100% FBP and 50% IR images in a randomized fashion for presence or absence of calculi in 9 regions (pyelocalyceal, proximal, mid, distal ureter, & bladder). Largest axial stone size on magnified bone windows per region was measured and categorized as ≤1,2-3, 4-5, 6-7, ≥8mm. Confidence scored on 5 point scale. Presence or absence of ancillary findings (hydronephrosis, stranding) or alternative diagnosis to explain flank pain was noted. Findings unrelated to history were scored using the CT colonography extracolonic reporting system. Truth was determined by 2 senior uroradiologists in consensus with access to medical record and other imaging. Nonparametric methods for clustered data were used to estimate the ROC curves and their areas for each reader. A 95% CI was constructed for the difference in the mean ROC areas. RESULTS 113 locations had stones & 752 did not (86 pyelocalyceal, 7 proximal, 4 mid, 15 distal ureter). Mean ROC area for FBP was 0.879 (range 0.607-0.967) and 50% IR was 0.883 (0.646-0.971). For one reader, ROC area with 50% IR was significantly better. The p-value for the hypothesis of non-inferiority was 0.001, indicating that 50% dose IR was not inferior. The 95% CI for the difference in ROC areas between 100% FBP vs. 50% IR is [-0.025, +0.031]. There was hydronephrosis or stranding in 23, an alternate diagnosis to explain pain in 1, clinically unimportant incidental findings in 37, likely unimportant findings in 5, and potentially significant findings in 9 patients. CONCLUSION 50% CT dose reconstructed with IR was equivalent to standard dose reconstructed with conventional FBP to detect urolithiasis. CLINICAL RELEVANCE/APPLICATION 50% dose reduction does not alter urolithiasis identification efficacy.
    Radiological Society of North America 2013 Scientific Assembly and Annual Meeting; 12/2013
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    ABSTRACT: Accurate assessment of air density used to quantitatively characterize amount and distribution of emphysema in chronic obstructive pulmonary disease (COPD) subjects has remained challenging. Hounsfield units (HU) within tracheal air can be considerably less negative than -1000 HU. This study has sought to characterize the effects of improved scatter correction used in dual-source pulmonary computed tomography (CT). Dual-source dual-energy (DSDE) and single-source (SS) scans taken at multiple energy levels and scan settings were acquired for quantitative comparison using anesthetized ovine (n = 6), swine (n = 13), and a lung phantom. Data were evaluated for the lung, inferior vena cava, and tracheal segments. To minimize the effect of cross-scatter, the phantom scans in the DSDE mode were obtained by reducing the current of one of the tubes to near zero. A significant shift in mean HU values in the tracheal regions of animals and the phantom is observed, with values consistently closer to -1000 HU in DSDE mode. HU values associated with SS mode demonstrated a positive shift of up to 32 HU. In vivo tracheal air measurements demonstrated considerable variability with SS scanning, whereas these values were more consistent with DSDE imaging. Scatter effects in the lung parenchyma differed from adjacent tracheal measures. Data suggest that the scatter correction introduced into the dual-energy mode of imaging has served to provide more accurate CT lung density measures sought to quantitatively assess the presence and distribution of emphysema in COPD subjects. Data further suggest that CT images, acquired without adequate scatter correction, cannot be corrected by linear algorithms given the variability in tracheal air HU values and the independent scatter effects on lung parenchyma.
    Academic radiology 11/2013; 20(11):1334-1343. · 2.09 Impact Factor
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    ABSTRACT: We aimed to test the hypothesis that three-dimensional (3D) volume-based scoring of computed tomography (CT) images of the paranasal sinuses was superior to Lund-Mackay CT scoring of disease severity in chronic rhinosinusitis (CRS). We determined correlation between changes in CT scores (using each scoring system) with changes in other measures of disease severity (symptoms, endoscopic scoring, and quality of life) in patients with CRS treated with triamcinolone. The study group comprised 48 adult subjects with CRS. Baseline symptoms and quality of life were assessed. Endoscopy and CT scans were performed. Patients received a single systemic dose of intramuscular triamcinolone and were reevaluated 1 month later. Strengths of the correlations between changes in CT scores and changes in CRS signs and symptoms and quality of life were determined. We observed some variability in degree of improvement for the different symptom, endoscopic, and quality-of-life parameters after treatment. Improvement of parameters was significantly correlated with improvement in CT disease score using both CT scoring methods. However, volumetric CT scoring had greater correlation with these parameters than Lund-Mackay scoring. Volumetric scoring exhibited higher degree of correlation than Lund-Mackay scoring when comparing improvement in CT score with improvement in score for symptoms, endoscopic exam, and quality of life in this group of patients who received beneficial medical treatment for CRS.
    International Forum of Allergy and Rhinology 09/2013; · 1.00 Impact Factor
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    ABSTRACT: OBJECTIVE. The purpose of this article is to determine the decrease in volume CT dose index (CTDIvol) 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, CTDIvol, 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 CTDIvol 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 CTDIvol and DLP, respectively. RESULTS. The change to a weight-based protocol resulted in a statistically significant reduction in CTDIvol and DLP on three MDCT system models (p < 0.001). The largest average CTDIvol decrease was 13.9%, and the largest average DLP decrease was 16.1% on a 64-MDCT system. Both the CTDIvol 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.
    American Journal of Roentgenology 06/2013; 200(6):1298-1303. · 2.90 Impact Factor
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    ABSTRACT: PURPOSE The purpose of the study is to determine the total effective dose and cancer risk induced by treatment monitoring and surveillance CT scans in patients diagnosed with lymphoma. METHOD AND MATERIALS All patients diagnosed with lymphoma in 2008 were identified from a cancer center registry (N=111). CT dose data was retrieved in 76 patients (43 men, 33 women; 54 non-hodgkin’s lymphoma, 22 hodgkin’s lymphoma) from the electronic archive using optical character recognition software. Inclusion dates for dose data was from two months prior to treatment initiation through December 2011. Average follow up time was 26.7 months (range 1-40). Cumulative dose length product (DLP) for all head and neck examinations, and for all chest, abdomen, and pelvis examinations was calculated for each patient. Total effective dose was calculated for each patient during and following the treatment course using conversion factors of 0.015 times the DLP for chest, abdomen and pelvis exams, and 0.0031 for head and neck exams. Radiation-induced cancer risk was estimated based on data from BEIR VII. RESULTS Mean effective dose per patient for head and neck examinations was 5.6 mSv during treatment (N=9 patients) and 4.4 mSv after treatment (N=26). Mean effective dose per patient for chest, abdomen, and pelvis examinations was 26.7 mSv during treatment (N=43) and 44.1 mSv after treatment (N=59). Mean total effective dose per patient was 51.4 mSv (range 0.8-171). Mean cancer risk per patient defined as the US population averaged cancer mortality risk was 0.29% (0.01%-0.97%). CONCLUSION Mean cancer risk in lymphoma patients undergoing regular CT scans during the course of treatment as well during the surveillance period is relatively low. Therefore, mortality related to radiation-induced cancer should not be a consideration in determining radiologic follow-up in current lymphoma treatment protocols. CLINICAL RELEVANCE/APPLICATION The risk of radiation induced cancer should not be a consideration when using CT to assess treatment response and subsequent surveillance in lymphoma patients.
    Radiological Society of North America 2012 Scientific Assembly and Annual Meeting; 11/2012
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    ABSTRACT: 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. 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. 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). 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.
    American Journal of Roentgenology 07/2012; 199(1):8-18. · 2.90 Impact Factor
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    ABSTRACT: PURPOSE Evaluate the effect of sinogram affirmed iterative reconstruction (SAFIRE)(Siemens Healthcare) vs filtered back projection (FBP) on low contrast to noise ratio (LCNR) in the liver and in a low contrast phantom on full and lower dose exams METHOD AND MATERIALS Fourteen livers were scanned using a dual source MDCT (Definition FLASH)(Siemens Healthcare) without IV contrast enhancement (HIPAA compliant, IRB approved study). The raw data from both tubes (100% dose) were reconstructed using FBP while the raw data from one tube (50% dose) were reconstructed using FBP and SAFIRE. For correlation, a low contrast phantom (CIRS Helical CT Phantom) composed of spheres ranging from 9.5 mm-2.4 mm, 17, 6 & 4 H.U. below background (48 H.U.) was scanned at 100%, 70%, 50% & 30% dose, using the same MDCT scanner, with single source acquisition mode. Using a MATLAB program, same size ROI’s in the same slice location were obtained using the IVC as a low contrast object and the adjacent liver as background and for the low contrast objects and adjacent background in the phantom. Noise, contrast & LCNR were calculated. RESULTS In the liver at 50% dose using SAFIRE, noise was reduced 26.8% and LCNR between the liver and adjacent IVC increased 29.5% when compared to the 100% dose FBP. Noise reduction accounted for 88% of the increased LCNR. The improvement in contrast was not as consistent as the improved noise & LCNR, partly due to the CT number shift in the half dose images (likely because of slightly different amounts of scatter contribution to the 100% & 50% dose images). With the phantom, at 50% dose using SAFIRE, noise was reduced 36.3% and LCNR increased 31.4% when compared to 100% dose FBP. Noise reduction accounted for 70% of the increased LCNR. However, at 50% dose, the 2.4 mm & 3.2 mm objects were not detectable, regardless of reconstruction method. CONCLUSION 50% dose scans with SAFIRE in clinical cases and phantom studies show decreased noise and increased LCNR when compared to 100% & 50% dose FBP scans. The improved LCNR is primarily due to lower noise levels. However, at 50% dose, small, low contrast objects may be lost, regardless of reconstruction method. CLINICAL RELEVANCE/APPLICATION Lower dose SAFIRE improves low contrast ratio when compared to full dose filtered back projection primarily by noise reduction. However, lower dose images may obscure very small, low contrast objects.
    Radiological Society of North America 2011 Scientific Assembly and Annual Meeting; 12/2011
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    ABSTRACT: Although state-of-the-art CT provides accurate sub millimeter details of the size and location of renal stones, current routine clinical image analysis does not differentiate stone composition. This is particularly important in the case of uric acid (UA) stones (∼10% of cases), since urinary alkalinization can be prescribed to dissolve UA stones. Therefore, simple and reliable differentiation of UA vs. non-UA stone composition could potentially allow patients with UA stones to avoid invasive interventional urinary procedures for stone removal or external shock wave lithotripsy. This chapter describes a novel Dual-Energy CT (DECT) technique for renal stone differentiation, which is based on the difference in X-ray attenuation properties at high and low kV between UA- and non-UA-containing stones. The technique has been implemented on modern Dual-Source CT scanners which allow simultaneous Dual-Energy acquisition with high spatial resolution and immediate postprocessing using commercial algorithm available on the system. Principles of DECT imaging, acquisition parameters and postprocessing details are discussed. Diagnostic evaluation of three clinical cases is provided together with a summary of the results of all known validation studies performed both in vitro and in vivo. The reported accuracy and sensitivity of the UA vs. non-UA differentiation using DECT varied from 88 to 100%. Further improvement is expected with the second generation of Dual-Source scanners due to increased spectral separation.
    01/2011: pages 177-189;
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    ABSTRACT: The objective of this study was to investigate the effect on radiation dose and image quality of the use of additional spectral filtration for dual-energy CT using dual-source CT (DSCT). A commercial DSCT scanner was modified by adding tin filtration to the high-kV tube, and radiation output and noise were measured in water phantoms. Dose values for equivalent image noise were compared between the dual-energy mode with and without tin filtration and the single-energy mode. To evaluate dual-energy CT material discrimination, the material-specific dual-energy ratio for calcium and that for iodine were determined using images of anthropomorphic phantoms. Data were additionally acquired from imaging a 38-kg pig and an 87-kg pig, and the noise of the linearly mixed images and virtual noncontrast images was compared between dual-energy modes. Finally, abdominal dual-energy CT images of two patients of similar sizes undergoing clinically indicated CT were compared. Adding tin filtration to the high-kV tube improved the dual-energy contrast between iodine and calcium as much as 290%. Data from our animal study showed that tin filtration had no effect on noise in the dual-energy CT mixed images but decreased noise by as much as 30% in the virtual noncontrast images. Virtual noncontrast images of patients acquired using 100 and 140 kV with added tin filtration had improved image quality relative to those generated using 80 and 140 kV without tin filtration. Tin filtration of the high-kV tube of a DSCT scanner increases the ability of dual-energy CT to discriminate between calcium and iodine without increasing dose relative to single-energy CT. Furthermore, the use of 100- and 140-kV tube potentials allows improved dual-energy CT imaging of large patients.
    American Journal of Roentgenology 11/2010; 195(5):1164-74. · 2.90 Impact Factor
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    ABSTRACT: The purpose of this study was to investigate replacing unenhanced and arterial single-energy CT acquisitions after endovascular aneurysm repair with one dual-energy CT arterial acquisition. Thirty patients underwent arterial dual-energy CT (80 and 140 kVp) and venous single-energy CT (120 kVp) after endovascular aneurysm repair, and the radiation doses were compared with those of a standard triple-phase protocol. Both virtual unenhanced and arterial images were generated with dual-energy CT. Images were reviewed clinically for detection of endoleaks and evaluation of stent and calcium appearance. The aortic luminal attenuation on virtual unenhanced CT images was compared with that on previously acquired true unenhanced images. Virtual unenhanced, arterial, and venous images were compared for thrombus attenuation. Single-energy CT and dual-energy CT images were compared for noise. Replacement of two (unenhanced, arterial) of three single-energy CT acquisitions with one dual-energy CT acquisition resulted in 31% radiation dose savings. All images were clinically interpretable. Thoracic (32 +/- 2 vs 35 +/- 4 HU) and abdominal (30 +/- 3 vs 35 +/- 5 HU) aortic attenuation was similar on virtual unenhanced and true unenhanced images. Thrombus attenuation was similar on virtual unenhanced (32 +/- 6 HU), arterial phase (33 +/- 7 HU), and venous phase (34 +/- 6 HU) images. Decreased stent and calcium attenuation was observed at some locations on virtual unenhanced images. Noise in the thoracic (10 +/- 1 HU) and abdominal (12 +/- 2 HU) aorta was lower on virtual unenhanced images than on true unenhanced images (13 +/- 4 HU, 19 +/- 5 HU). Noise was comparable for dual-energy and single-energy CT (thorax, 16 +/- 2 vs 13 +/- 2 HU; abdomen, 21 +/- 3 vs 23 +/- 5 HU). Virtual unenhanced and arterial phase images derived from dual-energy CT can replace true unenhanced and arterial phase single-energy CT images in follow-up after endovascular aneurysm repair (except immediately after the procedure), providing comparable diagnostic information with substantial dose savings.
    American Journal of Roentgenology 08/2010; 195(2):486-93. · 2.90 Impact Factor
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    ABSTRACT: To evaluate the detectability of urinary stones on virtual nonenhanced images generated at pyelographic-phase dual-energy computed tomography (CT). This retrospective HIPAA-compliant study was institutional review board approved. All included patients had previously consented to the use of their medical records for research. Sixty-two patients (38 men, 24 women; age range, 35-91 years) had undergone CT urography, which consisted of nonenhanced and pyelographic-phase dual-energy CT performed by using a dual-source scanner. Commercial software was used to create virtual nonenhanced images by suppressing the iodine signal from the pyelographic-phase dual-energy CT scans. Two radiologists, in consensus, evaluated the virtual nonenhanced images for the presence of stones. Sensitivity for detecting stones was calculated on a per-stone basis. Sensitivity, specificity, and accuracy were also calculated on a per-renal unit (defined as the intrarenal collecting system and ureter of one kidney) basis. The true nonenhanced scan was considered the reference standard. A jackknife method was used because any patient may have multiple stones. Of 62 patients with 122 renal units, 21 patients with 25 renal units had a total of 43 stones (maximal transverse diameter range, 1-24 mm; median, 3 mm). The overall sensitivity for detecting stones was 63% (27 of 43 stones) per stone. Sensitivities were 29% (four of 14 stones) for 1-2-mm stones, 64% (nine of 14 stones) for 3-4-mm stones, 83% (five of six stones) for 5-6-mm stones, and 100% (nine of nine stones) for 7-mm or larger (7, 7, 7, 8, 8, 9, 11, 15, and 24 mm) stones. All three ureteral stones (3, 4, and 8 mm) were correctly identified. The sensitivity, specificity, and accuracy for detecting stones on a per-renal unit basis were 65% (17 of 26 renal units), 92% (88 of 96 renal units), and 86% (105 of 122 renal units), respectively. Virtual nonenhanced images generated at pyelographic-phase dual-energy CT enabled the detection of urinary stones with moderate accuracy. The detection of small (1-2-mm) stones was limited.
    Radiology 07/2010; 256(1):184-90. · 6.34 Impact Factor
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    ABSTRACT: The purpose of this study was to optimize CT arthrography technique and determine if dual energy CT (DECT) can provide any benefit over single energy CT (SECT). Iodinated contrast attenuation at different concentrations was measured using DECT and SECT at different beam energies (140, 120, and 80 kVp). Dose and noise were measured on phantoms at different tube currents. Three bovine femoral condyles with artificially created cartilage defects were scanned with dose-equivalent protocols. Contrast-to-noise ratio (CNR) between cartilage and iodine was measured, and the appearance of cartilage defects was graded by two readers. DECT scans were post-processed for iodine quantification. The beam energy 80 kVp had the highest iodine signal, 50% greater than DECT, 75% greater than 120 kVp, and 100% greater than 140 kVp. Noise was nearly identical for all techniques when dose was matched. The 80 kVp level had the highest CNR, 25% higher than 120 kVp and DECT, and 33% greater than 140 kVp. The 80 kVp technique was also preferred by both readers. DECT iodine quantification was significantly limited by the post-processing application, noise, and beam hardening. In this in-vitro study, the SECT 80 kVp CT arthrography technique was superior to currently performed 120 and 140 kVP SECT techniques and DECT.
    Skeletal Radiology 04/2010; 39(10):1025-31. · 1.74 Impact Factor
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    ABSTRACT: To determine the constancy of z-axis spatial resolution, CT number, image noise, and the potential for image artifacts for nonconstant velocity spiral CT data reconstructed using a flexibly weighted 3D filtered backprojection (WFBP) reconstruction algorithm. A WFBP reconstruction algorithm was used to reconstruct stationary (axial, pitch=0), constant velocity spiral (pitch = 0.35-1.5) and nonconstant velocity spiral CT data acquired using a 128 x 0.6 mm acquisition mode (38.4 mm total detector length, z-flying focal spot technique), and a gantry rotation time of 0.30 s. Nonconstant velocity scans used the system's periodic spiral mode, where the table moved in and out of the gantry in a cyclical manner. For all scan types, the volume CTDI was 10 mGy. Measurements of CT number, image noise, and the slice sensitivity profile were made for all scan types as a function of the nominal slice width, table velocity, and position within the scan field of view. A thorax phantom was scanned using all modes and reconstructed transverse and coronal plane images were compared. Negligible differences in slice thickness, CT number, noise, or artifacts were found between scan modes for data taken at two positions within the scan field of view. For nominal slices of 1.0-3.0 mm, FWHM values of the slice sensitivity profiles were essentially independent of the scan type. For periodic spiral scans, FWHM values measured at the center of the scan range were indistinguishable from those taken 5 mm from one end of the scan range. All CT numbers were within +/- 5 HU, and CT number and noise values were similar for all scan modes assessed. A slight increase in noise and artifact level was observed 5 mm from the start of the scan on the first pass of the periodic spiral. On subsequent passes, noise and artifact level in the transverse and coronal plane images were the same for all scan modes. Nonconstant velocity periodic spiral scans can achieve z-axis spatial resolution, CT number accuracy, image noise and artifact level equivalent to those for stationary (axial), and constant velocity spiral scans. Thus, periodic spiral scans are expected to allow assessment of four-dimensional CT data for scan lengths greater than the detector width without sacrificing image quality.
    Medical Physics 02/2010; 37(2):897-906. · 2.91 Impact Factor

Publication Stats

2k Citations
163.24 Total Impact Points

Institutions

  • 2006–2010
    • Mayo Foundation for Medical Education and Research
      • Department of Radiology
      Scottsdale, AZ, United States
  • 2005–2010
    • Mayo Clinic - Rochester
      • Department of Radiology
      Rochester, Minnesota, United States
  • 2008–2009
    • University of California, Los Angeles
      • Department of Radiology
      Los Angeles, CA, United States
  • 2005–2007
    • Siemens
      • Siemens Medical Solutions
      München, Bavaria, Germany