Image Quality Evaluation in Dual-Energy CT of the Chest, Abdomen, and Pelvis in Obese Patients With Deep Learning Image Reconstruction.

OBJECTIVE: The aim of this study was to evaluate image quality in vascular and oncologic dual-energy computed tomography (CT) imaging studies performed with a deep learning (DL)-based image reconstruction algorithm in patients with body mass index of ≥30. METHODS: Vascular and multiphase oncologic staging dual-energy CT examinations were evaluated. Two image reconstruction algorithms were applied to the dual-energy CT data sets: standard of care Adaptive Statistical Iterative Reconstruction (ASiR-V) and TrueFidelity DL image reconstruction at 2 levels (medium and high). Subjective quality criteria were independently evaluated by 4 abdominal radiologists, and interreader agreement was assessed. Signal-to-noise ratio (SNR) and contrast-to-noise ratio were compared between image reconstruction methods. RESULTS: Forty-eight patients were included in this study, and the mean patient body mass index was 39.5 (SD, 7.36). TrueFidelity-High (DL-High) and TrueFidelity-Medium (DL-Med) image reconstructions showed statistically significant higher Likert scores compared with ASiR-V across all subjective image quality criteria ( P < 0.001 for DL-High vs ASiR-V; P < 0.05 for DL-Med vs ASiR-V), and SNRs for aorta and liver were significantly higher for DL-High versus ASiR-V ( P < 0.001). Contrast-to-noise ratio for aorta and SNR for aorta and liver were significantly higher for DL-Med versus ASiR-V ( P < 0.05). CONCLUSIONS: TrueFidelity DL image reconstruction provides improved image quality compared with ASiR-V in dual-energy CTs obtained in obese patients.

White Paper of the Society of Computed Body Tomography and Magnetic Resonance on Dual-Energy CT, Part 4: Abdominal and Pelvic Applications.

This is the fourth of a series of 4 white papers that represent expert consensus documents developed by the Society of Computed Body Tomography and Magnetic Resonance through its task force on dual-energy computed tomography. This article, part 4, discusses DECT for abdominal and pelvic applications and, at the end of each, will offer our consensus opinions on the current clinical utility of the application and opportunities for further research.

White Paper of the Society of Computed Body Tomography and Magnetic Resonance on Dual-Energy CT, Part 3: Vascular, Cardiac, Pulmonary, and Musculoskeletal Applications.

This is the third of a series of 4 white papers that represent Expert Consensus Documents developed by the Society of Computed Body Tomography and Magnetic Resonance through its Task Force on dual-energy computed tomography. This paper, part 3, describes computed tomography angiography and thoracic, cardiac, vascular, and musculoskeletal clinical applications. At the end of the discussion of each application category (vascular, cardiac, pulmonary, and musculoskeletal), we present our consensus opinions on the current clinical utility of the application and opportunities for further research.

Image-based quantification of 3D morphology for bifurcations in the left coronary artery: Application to stent design.

BACKGROUND: Improved strategies for stent-based treatment of coronary artery disease at bifurcations require a greater understanding of artery morphology. OBJECTIVE: We developed a workflow to quantify morphology in the left main coronary (LMCA), left anterior descending (LAD), and left circumflex (LCX) artery bifurcations. METHODS: Computational models of each bifurcation were created for 55 patients using computed tomography images in 3D segmentation software. Metrics including cross-sectional area, length, eccentricity, taper, curvature, planarity, branching law parameters, and bifurcation angles were assessed using open-sources software and custom applications. Geometric characterization was performed by comparison of means, correlation, and linear discriminant analysis (LDA). RESULTS: Differences between metrics suggest dedicated or multistent approaches should be tailored for each bifurcation. For example, the side branch of the LCX (i.e., obtuse marginal; OM) was longer than that of the LMCA (i.e., LCXprox) and LAD (i.e., first diagonal; D1). Bifurcation metrics for some locations (e.g., LMCA Finet ratio) provide results and confidence intervals agreeing with prior findings, while revised metric values are presented for others (e.g., LAD and LCX). LDA revealed several metrics that differentiate between artery locations (e.g., LMCA vs. D1, LMCA vs. OM, LADprox vs. D1, and LCXprox vs. D1). CONCLUSIONS: These results provide a foundation for elucidating common parameters from healthy coronary arteries and could be leveraged in the future for treating diseased arteries. Collectively the current results may ultimately be used for design iterations that improve outcomes following implantation of future dedicated bifurcation stents. © 2015 Wiley Periodicals, Inc.

White Paper of the Society of Computed Body Tomography and Magnetic Resonance on Dual-Energy CT, Part 2: Radiation Dose and Iodine Sensitivity.

This is the second of a series of 4 white papers that represent Expert Consensus Documents developed by the Society of Computed Body Tomography and Magnetic Resonance through its task force on dual-energy computed tomography. This paper, part 2, addresses radiation dose and iodine sensitivity in dual-energy computed tomography.

White Paper of the Society of Computed Body Tomography and Magnetic Resonance on Dual-Energy CT, Part 1: Technology and Terminology.

This is the first of a series of 4 white papers that represent Expert Consensus Documents developed by the Society of Computed Body Tomography and Magnetic Resonance through its task force on dual-energy computed tomography (DECT). This article, part 1, describes the fundamentals of the physical basis for DECT and the technology of DECT and proposes uniform nomenclature to account for differences in proprietary terms among manufacturers.

Pancreas transplant imaging: how I do it.

Pancreas transplantation aims to restore physiologic normoglycemia in diabetic patients with glomerulopathy and avoid or delay the onset of diabetic retinopathy and arteriopathy. Simultaneous pancreas-kidney transplant is the most common approach, using a cadaveric pancreas donation in conjunction with either cadaveric or live donor renal transplant. Alternative techniques include pancreas after kidney transplant, in which the pancreas transplant is performed some years after renal transplant. Pancreas transplant alone is utilized rarely in diabetic patients with compensated renal function. Pancreas grafts have vascular and enteric connections that vary in their anatomic approach, and understanding of this is critical for imaging with ultrasonography, computed tomography, or magnetic resonance imaging. Imaging techniques are directed to display the pancreatic transplant arterial and venous vasculature, parenchyma, and intestinal drainage pathway. Critical vascular information includes venous thrombosis (partial or complete), arterial occlusion, or aneurysm. Parenchymal abnormalities are nonspecific and occur in pancreatitis, graft rejection, and subsequent graft ischemia. Peripancreatic fluid collections include hematoma/seroma, pseudocyst, and abscess. The latter two are related to pancreatitis, duct disruption, or leak from the duodenojejunostomy. An understanding of transplant anatomy and complications will lead to appropriate use of imaging techniques to diagnose or exclude important complications.

Contrast-induced nephropathy after a second contrast exposure.

BACKGROUND: The risk of contrast-induced nephropathy (CIN) after repeated contrast exposure has not been evaluated. METHODS: We prospectively evaluated the effects of two contrast exposures during an investigational study of a new computerized tomography (CT) scanner. Adult subjects who underwent a variety of contrast-enhanced imaging procedures with conventional apparatus, as part of routine care, were invited to undergo a second contrast-enhanced research scan. Subjects were required to have an estimated glomerular filtration rate (eGFR) >60 mL/min/1.73 m(2) and a serum creatinine (sCr) value measured immediately prior to the second contrast exposure that was <125% of that measured prior to the first imaging study. RESULTS: Twenty-eight subjects underwent a second contrast exposure after a mean interval of 20 +/- 13 days (75% males, 89% Caucasians, 21% diabetics, mean age 60.6 +/- 6 years, mean contrast volume 130 +/- 42 mL). There was a significant increase in mean sCr and decline in eGFR after the second contrast exposure (sCr 0.93 +/- 0.14 vs. 0.86 +/- 0.15 mg/dL prior, p = 0.027; eGFR 83.9 +/- 13.5 vs. 89.8 +/- 13 mL/min/1.73 m(2) prior, p = 0.028). Four subjects (14.3% of the population) developed CIN. CONCLUSION: Even in subjects with relatively preserved renal function there is a notable risk of CIN after repeated contrast exposure. This conclusion was unaltered by several sensitivity analyses.

Prospective and retrospective ECG gating for thoracic CT angiography: a comparative study.

OBJECTIVE: The objective of our study was to compare radiation dose, contrast load, thoracic aortic attenuation value, and image quality parameters of MDCT thoracic aortography performed with prospective and retrospective cardiac gating. MATERIALS AND METHODS: Studies were performed on 80 patients (prospective ECG gating, n = 40; retrospective ECG gating, n = 40) either being evaluated for thoracic aortic aneurysm (n = 23) or aortic dissection (n = 36) or undergoing postsurgical or postintervention follow-up (n = 21). Image acquisition parameters and radiation dose (CT dose index volume [CTDI(vol)] and dose-length product [DLP]) were obtained from image archival data. Contrast load and aortic attenuation values were obtained from a data registry. The comparative degrees of motion artifact and banding artifact were assessed on parasagittal maximum-intensity-projection (MIP) images and reformatted images in the plane of the aortic valve. RESULTS: CTDI(vol) and DLP in the prospective ECG-gating group was 28.8 +/- 2.12 mGy (mean +/- SD) and 833.7 +/- 115.77 mGy/cm, respectively, which are significantly lower (p < 0.001) than those values in the retrospective ECG-gating group (74.7 +/- 13.42 mGy and 2,547.3 +/- 553.27 mGy/cm). The average contrast load in the prospective gating group was 109.1 +/- 14.74 mL and in the retrospective gating group, 101.3 +/- 10.45 mL (p < 0.05). The average aortic attenuation values (in Hounsfield units) for the prospective and retrospective ECG-gated groups were 447.6 and 350.2 HU, respectively, for the mid ascending aorta, 413.6 and 325.7 HU for the mid aortic arch, 418.2 and 327.6 HU for the mid descending aorta, and 355.0 and 306.2 HU for the supraceliac aorta. Subjective scores of motion artifact and banding artifact were equivalent between the two groups. CONCLUSION: Compared with retrospective ECG-gated thoracic CT angiography, prospective ECG-gated thoracic CT angiography was associated with a lower radiation dose, slightly increased contrast load, increased aortic attenuation values, and equivalent image quality.

CT automated exposure control using a generalized detectability index.

PURPOSE: Identifying an appropriate tube current setting can be challenging when using iterative reconstruction due to the varying relationship between spatial resolution, contrast, noise, and dose across different algorithms. This study developed and investigated the application of a generalized detectability index ( d gen ' ) to determine the noise parameter to input to existing automated exposure control (AEC) systems to provide consistent image quality (IQ) across different reconstruction approaches. METHODS: This study proposes a task-based automated exposure control (AEC) method using a generalized detectability index ( d gen ' ). The proposed method leverages existing AEC methods that are based on a prescribed noise level. The generalized d gen ' metric is calculated using lookup tables of task-based modulation transfer function (MTF) and noise power spectrum (NPS). To generate the lookup tables, the American College of Radiology CT accreditation phantom was scanned on a multidetector CT scanner (Revolution CT, GE Healthcare) at 120 kV and tube current varied manually from 20 to 240 mAs. Images were reconstructed using a reference reconstruction algorithm and four levels of an in-house iterative reconstruction algorithm with different regularization strengths (IR1-IR4). The task-based MTF and NPS were estimated from the measured images to create lookup tables of scaling factors that convert between d gen ' and noise standard deviation. The performance of the proposed d gen ' -AEC method in providing a desired IQ level over a range of iterative reconstruction algorithms was evaluated using the American College of Radiology (ACR) phantom with elliptical shell and using a human reader evaluation on anthropomorphic phantom images. RESULTS: The study of the ACR phantom with elliptical shell demonstrated reasonable agreement between the d gen ' predicted by the lookup table and d ' measured in the images, with a mean absolute error of 15% across all dose levels and maximum error of 45% at the lowest dose level with the elliptical shell. For the anthropomorphic phantom study, the mean reader scores for images resulting from the d gen ' -AEC method were 3.3 (reference image), 3.5 (IR1), 3.6 (IR2), 3.5 (IR3), and 2.2 (IR4). When using the d gen ' -AEC method, the observers' IQ scores for the reference reconstruction were statistical equivalent to the scores for IR1, IR2, and IR3 iterative reconstructions (P > 0.35). The d gen ' -AEC method achieved this equivalent IQ at lower dose for the IR scans compared to the reference scans. CONCLUSIONS: A novel AEC method, based on a generalized detectability index, was investigated. The proposed method can be used with some existing AEC systems to derive the tube current profile for iterative reconstruction algorithms. The results provide preliminary evidence that the proposed d gen ' -AEC can produce similar IQ across different iterative reconstruction approaches at different dose levels.

Computed tomography angiography to evaluate thoracic outlet neurovascular compression.

The objective was to evaluate the efficacy of computed tomography angiography with upper extremity hyperabduction to diagnose thoracic outlet syndrome. Over 5 years, 21 patients were treated surgically for neurogenic symptoms of thoracic outlet syndrome. For patients whose diagnosis was unclear after history and physical examination, adjunctive tests (duplex, magnetic resonance angiography, or computed tomography angiography) were performed to help establish the diagnosis. Five of the 6 computed tomography angiograms were positive. The sixth computed tomography was deemed to be an incomplete study. With mean follow-up of 9.4 months, 95% (n = 19) of patients with a positive hyperabduction test on physical examination were free of symptoms postoperatively. All patients with a positive computed tomography angiogram, with their neurovascular compression localized to the thoracic outlet, had successful operative decompression. Computed tomography angiogram with abduction of the arm can be used as an adjunct to confirm the diagnosis of neurovascular compression and then predict successful operative decompression.

The role of sonography in imaging of the biliary tract.

Sonography is the recommended initial imaging test in the evaluation of patients presenting with right upper quadrant pain or jaundice. Dependent upon clinical circumstances, the differential diagnosis includes choledocholithiasis, biliary stricture, or tumor. Sonography is very sensitive in detection of mechanical biliary obstruction and stone disease, although less sensitive for detection of obstructing tumors, including pancreatic carcinoma and cholangiocarcinoma. In patients with sonographically documented cholelithiasis and choledocholithiasis, laparoscopic cholecystectomy with operative clearance of the biliary stone disease is usually performed. In patients with clinically suspected biliary stone disease, without initial sonographic documentation of choledocholithiasis, endoscopic ultrasound or magnetic resonance cholangiopancreatography is the next logical imaging step. Endoscopic ultrasound documentation of choledocholithiasis in a postcholecystectomy patient should lead to retrograde cholangiography, sphincterotomy, and clearance of the ductal calculi by endoscopic catheter techniques. In patients with clinical and sonographic findings suggestive of malignant biliary obstruction, a multipass contrast-enhanced computed tomography (CT) examination to detect and stage possible pancreatic carcinoma, cholangiocarcinoma, or periductal neoplasm is usually recommended. Assessment of tumor resectability and staging can be performed by CT or a combination of CT and endoscopic ultrasound, the latter often combined with fine needle aspiration biopsy of suspected periductal tumor. In patients whose CT scan suggests hepatic hilar or central intrahepatic biliary tumor, percutaneous cholangiography and transhepatic biliary stent placement is usually followed by brushing or fluoroscopically directed fine needle aspiration biopsy for tissue diagnosis. Sonography is the imaging procedure of choice for biliary tract intervention, including cholecystostomy, guidance for percutaneous transhepatic cholangiography, and drainage of peribiliary abscesses.

Quality assurance methods for the first Radiation Therapy Oncology Group permanent prostate implant protocol.

PURPOSE: To report the quality assurance methodology used by the Radiation Therapy Oncology Group in the first cooperative group, multi-institution Phase II trial of transrectal ultrasound guided permanent radioactive implantation of the prostate for definitive treatment of localized adenocarcinoma of the prostate. METHODS AND MATERIALS: Participating institutions were credentialed to participate in this protocol, Radiation Therapy Oncology Group 98-05. International Commission on Radiation Units and Measurements (ICRU) Report 58 was used as the basis for definition of terms. The AAPM's dosimetric prerequisites for low energy interstitial brachytherapy sources were adopted. A nondigital approach to central review was used. The implant dosimetry was recalculated based upon centrally reviewed target volumes by both a radiation oncologist and a diagnostic radiologist. RESULTS: There are differences in the definition of the postimplant prostate between the participating institution, the central review radiation oncologist, and the central review diagnostic radiologist. Thus, there are differences in dose/volume parameters. Six of the 95 patients reviewed did not meet the per protocol criteria based upon information supplied by the participating institution. This increased to 18 cases when using the postimplant target volume defined by the central oncologist and to 23 cases when defined by the radiologist. CONCLUSIONS: This work indicated that there is a need for a central review process of dose-volume analysis within the cooperative group setting. It is indicated that a digital approach to centralized review, which has now been developed, would result in a higher quality and easier review.

Feasibility and validation of registration of three-dimensional left atrial models derived from computed tomography with a noncontact cardiac mapping system.

OBJECTIVES: The purpose of this study was to determine the feasibility and assess the validity of registering three-dimensional (3D) models from computed tomographic (CT) images using a cardiac mapping system. BACKGROUND: Registration of 3D anatomic models with an interventional system could help identify and navigate mapping and ablation catheters over a complex structure such as the left atrium (LA). METHODS: ECG-gated, contrast-enhanced cardiac CT imaging was performed in 14 patients with atrial fibrillation. Segmentation was used to create 3D models of the LA. The 3D models were registered with the mapping system using a series of fiducial points. Registration was accomplished retrospectively in the first 10 patients, and catheter navigation was visualized from recorded data. In the final four patients, registration was accomplished in real time during electrophysiologic study. The mapping catheter position, as it was navigated inside the LA, was applied to the registered model in real time. For the validation study, temporary pacing leads were implanted in the LA of 10 dogs. Following this, CT scanning, segmentation, LA model importation, and registration was described previously. After registration, a mapping catheter was positioned at the site of each buried lead according to the registered model with no fluoroscopic guidance. A radiofrequency lesion was created at this location, and the dog was sacrificed, the heart removed and stained, and the distance between the buried lead and the lesion measured. RESULTS: During the feasibility study, the location of the catheter in the registered model correlated with fluoroscopy, angiography, and intracardiac electrograms. LA endocardial potentials during sinus rhythm and any premature atrial contractions also were successfully delineated over the registered models. In the validation study, the mean target registration error was 2.0 +/- 3.6 mm. CONCLUSIONS: Registration of CT-derived 3D models of the LA using a cardiac mapping system is feasible and accurate.

Image Interpretation Session: Sunday, November 27, 2005.

The Sunday afternoon Image Interpretation Session has been a high point of the annual meeting of the Radiological Society of North America for over 65 years. A panel of five experts has been selected, representing the very best from the fields of neurologic, abdominal, thoracic, pediatric, and musculoskeletal radiology. Each panelist will dazzle us with an insightful analysis of two difficult cases in their area of expertise. The panelists are to be lauded for their bravery in subjecting their diagnostic acumen to the scrutiny of the thousands of radiologists in the audience. The cases, representing a diverse spectrum of diseases and disease manifestations, were selected from recent clinical imaging studies performed at the Stanford University Medical Center or the Lucille Salter Packard Children's Hospital. This session celebrates the skills of diagnostic radiologists worldwide, who are called on daily to amalgamate disparate clinical information with complex imaging data into focused differential diagnoses and effective treatment planning. We hope that these cases will serve to illustrate the central role that expert image interpretation plays in the care of patients. We welcome our audience of RSNA attendees, readers of RadioGraphics, and cyberspace denizens to join with our experts in solving these medical puzzles and to enjoy the excitement of unraveling the unknown.

Renal MDCT.

Multidetector CT has expanded the utility of CT by improving longitudinal resolution and acquisition speed. Applications include diagnosis of renal vascular and parenchymal injuries, renal tumor diagnosis and staging, the emerging field of CT urography and CT angiography. This summary review illustrates MDCT approaches to the evaluation of trauma, suspected tumor and imaging of the urinary tract and discusses other applications in renal inflammatory disease, urolithiasis and renal anomalies.

Abdominal MDCT: liver, pancreas, and biliary tract.

Multidetector row computed tomography (MDCT) enables rapid thin-section acquisition of regional body anatomy. MDCT is adapted to hepatic and pancreatic imaging to produce, in appropriate clinical circumstances, a multipass multiplanar study obtained during defined circulatory phases to best outline vasculature and detect and characterize focal parenchymal lesions. In this chapter, a rational approach to hepatic and pancreatic MDCT acquisition is outlined with emphasis on circulatory phases and contrast material pharmacokinetics as well as biological characteristics of focal parenchymal lesions.

Scrotal ultrasonography with emphasis on the extratesticular space: anatomy, embryology, and pathology.

Sonography is the imaging modality of choice in detecting and characterizing pathologic conditions affecting the extratesticular space. Although most abnormalities are benign, many may simulate or represent malignant processes. Accurate diagnosis is therefore essential and must be based not only on the sonographic findings but also on accurate clinical history and physical examination findings. This article reviews the anatomy, embryologic development, and pathologic conditions affecting the extratesticular space.