Whole-Body High-Pitch CT Angiography: Strategies to Reduce Radiation Dose and Contrast Volume.

OBJECTIVE: The purpose of this study was to assess the noninferiority of dual-source high-pitch CT angiography (CTA) performed with high-concentration (iopamidol 370) low-volume (60 mL) iodinated contrast material at low voltage (100 kVp) in comparison with dual-source high-pitch CTA with standard-of-care low-concentration (iopamidol 300) standard-volume (75 mL) iodinated contrast material at high voltage (120 kVp) to determine whether use of the high-concentration low-volume method would afford a reduction in radiation dose and contrast volume without negatively affecting vascular opacification. SUBJECTS AND METHODS: This study had three arms. A phantom was used to assess vascular contrast enhancement at different iodine and saline solution dilutions with iopamidol 300 or 370 to compare lower-iodination (iopamidol 300) high-voltage (120 kVp) high-pitch (120 kVp, 250 mAs) imaging with higher-iodination (iopamidol 370) low-voltage (100 kVp) high-pitch (100 kVp, 100-240 mAs) acquisition. Metal-oxide-semiconductor field-effect transistors were placed in an anthropomorphic phantom to extract organ-based radiation profiles, and ANOVA was performed. The study prospectively enrolled 150 patients: 50 patients received 75 mL iopamidol 300, and image acquisition was performed at 120 kVp and 250 mAs; 50 patients received 75 mL iopamidol 370, and acquisition was performed at 100 kVp and 240 mAs; and 50 patients received 60 mL iopamidol, and acquisition was performed at 370 at 100 kVp and 240 mAs. Vascular signal-to-noise ratio was evaluated at 18 anatomic locations. Longitudinal signal-to-noise ratio was used to assess homogeneity of contrast enhancement. Size-specific dose estimates were calculated. Statistical analyses were performed by ANOVA. RESULTS: Noninferiority of high-concentration (iopamidol 370) low-voltage (100 kVp) high-pitch acquisitions compared with low-concentration (iopamidol 300) high-voltage (120 kVp) high-pitch acquisition was achieved at 170 mAs in vitro. Radiation assessment showed significant decreases in radiation dose for the 100-kVp 240-mAs protocol (p < 0.0001). Noninferior vascular contrast (p > 0.280) and luminal homogeneity (p > 0.191) were found for all high-pitch protocols. Significantly decreased radiation dose was observed for the two groups that received 60 and 75 mL of iopamidol 370 at 100 kVp and 240 mAs (p < 0.0001). CONCLUSION: Dual-source high-pitch CTA with high-concentration (iopamidol 370) low-volume (60 mL) iodinated contrast medium and low-voltage acquisition (100 kVp) is noninferior to dual-source high-pitch CTA with low-concentration (iopamidol 300) standard-volume (75 mL) iodinated contrast material at high voltage (120 kVp) and affords simultaneous reduction in radiation dose and contrast volume without negatively affecting vascular contrast enhancement.

High-Pitch Dual-Source MDCT for Imaging of the Thoracoabdominal Aorta: Relationships Among Radiation Dose, Noise, Pitch, and Body Size in a Phantom Experiment and Clinical Study.

OBJECTIVE: The purpose of this study was to investigate, both in a phantom experiment and a within-patient clinical study the relationships among radiation dose, image noise, pitch, and body size in MDCT angiography of the thoracoabdominal aorta, with the use of high-pitch dual-source and standard-pitch single-source acquisitions. MATERIALS AND METHODS: A proprietary tapered phantom consisting of four ultrahigh-molecular-weight polyethylene cylinders was used to mimic the body size ranges (small, medium, large, and extra large) of patients in the United States. The phantom was imaged using both standard-pitch (0.8) and various high-pitch (range, 2.0-3.2 [in increments of 0.4]) settings. Standard-pitch and high-pitch acquisitions were also performed in 45 patients (27 men, 18 women; mean age, 67.6 years). RESULTS: At standard pitch, the volume CT dose index (CTDIvol) increased with phantom size, in a logistic sigmoid relationship. At high-pitch settings, the CTDIvol increased gradually in relation to phantom size, up to a threshold (denoted by tCTDI[pitch] ≈ 48.3-7.5 pitch), which linearly decreased (R(2) = 0.99) with pitch (maximum CTDIvol output at pitch [maxCTDI(pitch)] ≈ 18.9-3.9 pitch). A linear decrease in the size-specific dose estimate (SSDE) was observed beyond phantom size thresholds (tSSDE[pitch] ≈ 47.6-8.6 pitch) linearly decreasing (R(2) = 0.98) with pitch (maximum SSDE output at pitch [maxSSDE(pitch)] ≈ 15.5-1.3 pitch). Image noise was statistically significantly lower at standard pitch than at high-pitch settings (p = 0.01). In patients, statistically significant differences were noted between standard and high-pitch settings in the mean CTDIvol(10.8 ± 2.6 and 8.3 ± 0.7 mGy, respectively), SSDE (11.3 ± 2.1 and 8.8 ± 1.5 mGy, respectively), and noise (9.7 ± 2.2 and 14 ± 4.2, respectively) (p < .0001, for all comparisons). CONCLUSION: Lower radiation dose levels achieved with the use of a high-pitch technique reflect limitations in tube output occurring for medium to large body sizes, with an associated exponential increase in noise. The standard- and high-pitch techniques yield similar radiation dose levels for small body sizes.

Dual-Energy Multidetector-Row Computed Tomography of the Hepatic Arterial System: Optimization of Energy and Material-Specific Reconstruction Techniques.

PURPOSE: To investigate the optimal dual-energy reconstruction technique for the visualization of the hepatic arterial system during dual-energy multidetector computed tomographic (MDCT) angiography of the liver. MATERIALS AND METHODS: Twenty-nine nonconsecutive patients underwent dual-energy MDCT angiography of the liver. Synthesized monochromatic (40, 50, 60, and 80 keV) and iodine density data sets were reconstructed. Aortic attenuation, noise, and contrast-to-noise ratio (CNR) were measured. In addition, volume-rendered images were generated and qualitatively assessed by 2 independent readers, blinded to technique. The impact of body size on the readers' scores was also assessed. RESULTS: Aortic attenuation, noise, and CNR increased progressively with decreasing keV and were significantly higher between 40 and 60 keV (P < 0.001). There was a significant improvement of readers' visualization of arterial anatomy at lower monochromatic energies (P < 0.001). Iodine density images yielded significantly higher CNR compared with all monochromatic data sets (P < 0.001). However, iodine density images were scored nondiagnostic by the 2 readers. CONCLUSIONS: Synthesized monochromatic images between 40 and 60 keV maximize the magnitude of arterial enhancement and improve visualization of hepatic arterial anatomy at dual-energy MDCT angiography of the liver. Larger body sizes may counteract the benefits of using lower monochromatic energies.

Occupational and environmental lung disease.

Occupational and environmental lung disease remains a major cause of respiratory impairment worldwide. Despite regulations, increasing rates of coal worker's pneumoconiosis and progressive massive fibrosis are being reported in the United States. Dust exposures are occurring in new industries, for instance, silica in hydraulic fracking. Nonoccupational environmental lung disease contributes to major respiratory disease, asthma, and COPD. Knowledge of the imaging patterns of occupational and environmental lung disease is critical in diagnosing patients with occult exposures and managing patients with suspected or known exposures.

Characterizing search, recognition, and decision in the detection of lung nodules on CT scans: elucidation with eye tracking.

PURPOSE: To determine the effectiveness of radiologists' search, recognition, and acceptance of lung nodules on computed tomographic (CT) images by using eye tracking. MATERIALS AND METHODS: This study was performed with a protocol approved by the institutional review board. All study subjects provided informed consent, and all private health information was protected in accordance with HIPAA. A remote eye tracker was used to record time-varying gaze paths while 13 radiologists interpreted 40 lung CT images with an average of 3.9 synthetic nodules (5-mm diameter) embedded randomly in the lung parenchyma. The radiologists' gaze volumes ( GV gaze volume s) were defined as the portion of the lung parenchyma within 50 pixels (approximately 3 cm) of all gaze points. The fraction of the total lung volume encompassed within the GV gaze volume s, the fraction of lung nodules encompassed within each GV gaze volume (search effectiveness), the fraction of lung nodules within the GV gaze volume detected by the reader (recognition-acceptance effectiveness), and overall sensitivity of lung nodule detection were measured. RESULTS: Detected nodules were within 50 pixels of the nearest gaze point for 990 of 992 correct detections. On average, radiologists searched 26.7% of the lung parenchyma in 3 minutes and 16 seconds and encompassed between 86 and 143 of 157 nodules within their GV gaze volume s. Once encompassed within their GV gaze volume , the average sensitivity of nodule recognition and acceptance ranged from 47 of 100 nodules to 103 of 124 nodules (sensitivity, 0.47-0.82). Overall sensitivity ranged from 47 to 114 of 157 nodules (sensitivity, 0.30-0.73) and showed moderate correlation (r = 0.62, P = .02) with the fraction of lung volume searched. CONCLUSION: Relationships between reader search, recognition and acceptance, and overall lung nodule detection rate can be studied with eye tracking. Radiologists appear to actively search less than half of the lung parenchyma, with substantial interreader variation in volume searched, fraction of nodules included within the search volume, sensitivity for nodules within the search volume, and overall detection rate.

Imaging of complications of thoracic and cardiovascular surgery.

Iatrogenic complications of thoracic and cardiovascular surgery are relatively uncommon, but contribute to potentially significant patient morbidity and mortality. The incidence of iatrogenic disease reflects the complexity of surgical procedures, including lung resection, esophagectomy, coronary artery bypass grafting, thoracic aorta repair, and cardiac valve replacement. Some iatrogenic complications are minor and common to all procedures, whereas others can be potentially devastating and are associated with precise technical components of specific surgeries. Multimodality imaging plays an important role in the diagnosis and management of operative thoracic and cardiovascular iatrogenic disease.

Assessment of vascular contrast and wall motion of the aortic root and ascending aorta on MDCT angiography: dual-source high-pitch vs non-gated single-source acquisition schemes.

OBJECTIVES: This retrospective study assessed whether dual-source high-pitch computed tomographic angiography (CTA) offered advantages over single-source standard-pitch techniques in the evaluation of the ascending aorta. METHODS: Twenty patients who received both thoracic dual-source high-pitch and single-source standard-pitch CTAs within 1 year were assessed. Dual-source CTAs were performed; standard-pitch imaging used dose-modulated 120 kVp/150 mAs and 0.8 pitch compared with high-pitch protocols employing dose-modulated 120 kVp/250 mAs and 2.4 target pitch. Radiation dose was documented. Contrast-to-noise ratios (CNRs) at sinuses of the Valsalva (CNRValsalva) and ascending aorta (CNRAorta) were calculated. Dose/CNR for each technique was compared with paired t-tests. Motion at aortic valve, aortic root and ascending aorta were assessed with four-point scales and Mann-Whitney U tests; longitudinal extension of motion was compared with paired t-tests. RESULTS: Significantly lower motion scores for high-pitch, compared with standard-pitch acquisitions for aortic annulus, 0 vs. 2, aortic root, 0 vs. 3, and ascending aorta, 0 vs. 2, were achieved. Significantly reduced longitudinal extension of motion at aortic root, 4.9 mm vs 15.7 mm, and ascending aorta, 4.9 mm vs 21.6 mm, was observed. Contrast was not impacted: CNRValsalva, 45.6 vs 46.3, and CNRAorta, 45.3 vs 47.1. CTDIvol was significantly decreased for high-pitch acquisitions, 13.9 mGy vs 15.8 mGy. CONCLUSIONS: Dual-source high-pitch CTAs significantly decreased motion artefact without negatively impacting vascular contrast and radiation dose. KEY POINTS: • Dual-source high-pitch CTA significantly decreased motion artefact of the ascending aorta. • Dual-source high-pitch CTA did not negatively impact on vascular contrast. • Dual-source high-pitch CTA significantly decreased radiation dose compared with single-source standard-pitch acquisitions.

Impact of phase of respiration on central venous catheter tip position.

PURPOSE: To determine the impact of the phase of respiration on CVC tip position using cross-sectional imaging. METHODS: We retrospectively analyzed the CT scans of 24 consecutive patients (eight men and 16 women, mean age 56.3 years, range 18-79) who underwent a CT scan protocol that includes both imaging of the thorax in inspiration and expiration. Only patients with a central venous catheter and absence of any substantial pulmonary pathology that might affect lung volumes were included. Measurements of the catheter tip location and central venous structures were obtained from inspiratory and expiratory phase images in each patient and compared using the paired t test. RESULTS: The length of the SVC and superior mediastinum were significantly longer during inspiration compared to expiration (9 mm and 7 mm respectively, P<0.001 for both). The distance between the superior and inferior cavo-atrial junction did not change significantly with respiration. The catheter tip location moved on average 9 mm (range 0-25 mm) cephalad during inspiration compared to expiration (P=0.001) in relation to the superior cavoatrial junction. The amount of catheter tip movement correlated significantly with the degree of diaphragmatic excursion with respiration (R=0.58). During inspiration, the cavo-atrial junction was on average 11 mm inferior to the right cardiomediastinal angle observed on radiography, but was nearly identical during expiration (R=0.78, P<0.001). CONCLUSIONS: The central catheter tip position varied significantly with respiratory motion, with a mean excursion of 9 mm. The right cardiomediastinal border demonstrated a strong correlation with the actual location of the superior cavo-atrial junction in expiration, but not in inspiration.

Diffuse cystic lung disease at high-resolution CT.

OBJECTIVE: This article will illustrate and describe the spectrum of diseases associated with air cysts at high-resolution CT (HRCT). CONCLUSION: HRCT is an important modality in the evaluation of interstitial lung disease to include cystic lung disease. Although most commonly associated with lymphangioleiomyomatosis or Langerhans cell histiocytosis, cystic lung disease is increasingly being recognized as a feature of other entities. Awareness of the spectrum of HRCT findings associated with these diseases may help the trained observer narrow the differential diagnosis.

Comparison of ECG-gated rectilinear vs. real-time radial K-space sampling schemes in cine True-FISP cardiac MRI.

PURPOSE: To compare three k-space sampling schemes in cine True-FISP cardiac magnetic resonance imaging and to evaluate changes in calculated quantitative functional cardiac parameters as a function of underlying k-space sampling techniques. MATERIAL AND METHODS: Using a 1.5 T MR imaging system (Magnetom Sonata, Siemens Medical Solutions, Erlangen, Germany), three k-space data-sampling schemes: rectilinear (2.96 ms/1.58 ms/70 degrees /12 s TR/TE/FA/AcquisitionTime), and two radial k-space acquisitions, with filtered back-projection (RADIAL) (2.45 ms/1.25 ms/ 50 degrees /3.3 s TR/TE/FA/AT), and steady-state projection imaging with dynamic echotrain readout (SPIDER) (3.39 ms/1.62 ms/55 degrees /1.8 s TR/TE/FA/AT) of a True-FISP sequence were applied in 10 healthy volunteers. Long- and short-axis breath-hold series were acquired and signal-to-noise ratios (SNR) for blood and myocardium were determined, as was contrast-to-noise ratios (CNR). Quantitative cardiac functional analysis included: determination of end-systolic/end-diastolic volumes, ejection fraction, and left ventricular mass. Functional analysis was performed by two independent readers three times for each volunteer and k-space sampling strategy. Statistical analysis evaluated the accuracy of the measurements obtained from each of the three sampling techniques and the intra- and interobserver reliability. RESULTS: Intraobserver and interobserver reliability measures of functional data were homogeneous without statistically significant differences. Intraobserver correlation coefficients ranged from 0.94-0.99; interobserver correlation coefficients ranged from 0.97-0.99. Direct comparison of SPIDER- and RADIAL-sampled True-FISP sequences showed no statistically significant differences in measured functional parameters with interstudy correlation coefficients from 0.88-0.98. RADIAL and SPIDER images had better temporal resolution and were qualitatively judged to provide superior wall/blood border definition. Statistically significant differences were identified in each volumetric functional parameter when results from the rectilinear sampling acquisitions were compared with either radial or SPIDER sampling techniques. RADIAL and SPIDER results were consistently higher than volumetric measures obtained from the rectilinear data set. CONCLUSION: Employing faster sampling schemes led to enhanced signal homogeneity while maintaining the necessary CNR for estimation of functional cardiac parameters. Enhanced signal homogeneity and maintained CNR will most likely improve the accuracy of the cardiac functional parameter determination.