Reconstructed Slice Thickness Research Articles

Robust, Standardized Quantification of Pulmonary Emphysema in Low Dose CT Exams

The aim of this study was to present and evaluate a fully automated system for emphysema quantification on low-dose computed tomographic images. The platform standardizes emphysema measurements against changes in the reconstruction algorithm and slice thickness. Emphysema was quantified in 149 patients using a fully automatic, in-house developed software (the Robust Automatic On-Line Pulmonary Helper). The accuracy of the system was evaluated against commercial software, and its reproducibility was assessed using pairs of volume-corrected images taken 1 year apart. Furthermore, to standardize quantifications, the effect of changing the reconstruction parameters was modeled using a nonlinear fit, and the inverse of the model function was then applied to the data. The association between quantifications and pulmonary function testing was also evaluated. The accuracy of the in-house software compared to that of commercial software was measured using Spearman's rank correlation coefficient, the mean difference, and the intrasubject variability. Agreement between the methods was studied using Bland-Altman plots. To assess the reproducibility of the method, intraclass correlation coefficients and Bland-Altman plots were used. The statistical significance of the differences between the standardized data and the reference data (soft-tissue reconstruction algorithm B40f; slice thickness, 1 mm) was assessed using a paired two-sample t test. The accuracy of the method, measured as intrasubject variability, was 3.86 mL for pulmonary volume, 0.01% for emphysema index, and 0.39 Hounsfield units for mean lung density. Reproducibility, assessed using the intraclass correlation coefficient, was >0.95 for all measurements. The standardization method applied to compensate for variations in the reconstruction algorithm and slice thickness increased the intraclass correlation coefficients from 0.87 to 0.97 and from 0.99 to 1.00, respectively. The correlation of the standardized measurements with pulmonary function testing parameters was similar to that of the reference (for the emphysema index and the obstructive subgroup: forced expiratory volume in 1 second, -0.647% vs -0.615%; forced expiratory volume in 1 second/forced vital capacity, -0.672% vs -0.654%; and diffusing capacity for carbon monoxide adjusted for hemoglobin concentration, -0.438% vs -0.523%). The new emphysema quantification method presented in this report is accurate and reproducible and, thanks to its standardization method, robust to changes in the reconstruction parameters.

Assessment of the cerebellar arteries with multidetector computed tomography angiography benefits from submillimeter slice thickness

Purpose To evaluate the accuracy of 64-row-multidetector computed tomography (MDCT) with different slice thickness (0.625 vs. 1.25 mm) in assessing the cerebellar arteries. Materials and methods A total of 21 consecutive patients who underwent computed tomography angiography (CTA) of the cervicocranial arteries (64-row MDCT; slice thickness, 0.625 mm) because of suspicion of cerebral ischemia were enrolled retrospectively. The MDCT data set was secondarily reconstructed to a slice thickness of 1.25 mm. The examinations were reviewed by three independent blinded observers. Recorded parameters for reconstructed slice thicknesses of 0.625 compared to 1.25 mm were visualization and edge enhancement (based on a developed phantom reference model) of the cerebellar arteries including anterior and posterior inferior cerebellar arteries and the superior cerebellar artery. Results With 0.625-mm slices, significantly more vessel segments were visualized and edge enhancement was superior compared to 1.25-mm slices by the three readers, and a significant difference for the interaction between vessel segments and the slice thickness was found ( P<.001). Furthermore, for a slice thickness of 1.25 mm, there was a significant difference in visualization ( P=.0042) and edge enhancement ( P=.0015) of vessel segments between the three readers, whereas for thinner slices (0.625 mm), no significant differences were found ( P=.412, P=.465). Conclusions MDCT with slice thickness of 0.625 mm is superior to 1.25 mm reconstructed slice thickness regarding the visualization of cerebellar arteries, representative for smallest assessable arteries in CTA. This is paralleled by a sharper edge enhancement of the vessel contours resulting from a reduced partial volume effect. Conclusively, cranial CTA protocols should be routinely optimized to generate submillimeter slices for diagnostic purposes and digital storage as additional diagnostic value can be expected.

SU‐E‐I‐28: Pitch and Noise in Abdominal Multi‐Detector CT

Purpose: To quantify the effect of pitch on noise in abdominal multi‐detector CT. Methods: The standard acrylic abdominal CTDI phantom was modified so that it could be supported on the gantry shroud and remain stationary during a helical multi‐detector CT image acquisition. The table top height was positioned 1 cm below the phantom so that the table could move during helical image acquisition without touching the phantom. The phantom was scanned with the x‐ray tube voltage, x‐ray tube anode current, reconstructed slice thickness, multi‐detector selection and reconstruction kernel typically employed in a standard abdominal protocol for the different pitches available. On a given unit only the pitch was varied. The pixel standard deviation (noise) for four small (100 mm2) centrally located regions of interest were measured and averaged. Sixteen slice and 64 slice multi‐detector CT scanners were studied. On both scanners the standard filtered backprojection image reconstruction (FBP) algorithm was utilized. Results: On both the 16 slice and 64 slice scanners the noise varied to a reasonable approximation with the square root of the pitch for pitches ranging from ∼0.5 to ∼1.0. On the 16 slice scanner the noise increased only slightly when the pitch was changed from 1.375 to 1.75 Conclusions: In the cases of the CT scanners studied our results support the widely accepted fact that noise in an abdominal (noncardiac) mode multi‐detector helical CT image varies with pitch (and to the first order with the square root of the pitch) for pitches up to one when the FBP algorithm is employed. Our results do not support this fact when the pitch is increased above 1.0 and in particular as the pitch is increased to 1.75.

SU-E-I-156: CT Dose in Pediatric PET/CT Examinations

Purpose: To optimize CT protocols for pediatric whole-body PET/CT examination and to evaluate radiation dose. Methods: We developed pediatric whole-body CT acquisition protocols used for attenuation correction and localization of the PET data. Patients were categorized in 6 groups according to their weight and age, similar to the Broselow—Luten color-coded scale. X-ray tube current modulation was employed in all protocols with maximum mAs ranging from 25 to 55. The acquisition parameters were as follows: 100 kVp; 16×1.25 mm X-ray beam collimation; 27.1 Noise Index; 1.35:1 pitch; 0.5 s rotation time; and 3.75 mm reconstructed slice thickness. For the senior group of 12 – 17 years of age (50 – 70 kg) we used 120 kVp and 50 max mAs. All data were acquired on a GE Discovery STE 16 PET/CT scanner, and patients were injected with 5.55 MBq (0.15 mCi) of 18F-FDG per kg of weight. We surveyed pediatric studies performed in our institution during the period of 2009 – 2010. There were 27 patients from 18 months to 17 years of age, and 12 of them had had multiple exams (up to 6). Overall, 54 pediatric studies were performed over the two-year period. Effective CT dose was calculated using the dose length product (DLP) values from the patientsˈ dose reports and conversion factors (normalized effective dose per DLP), dependant on the patient age. Results: Effective CT doses were in the range from 0.91 mSv to 3.6 mSv for all patient categories. Comparison with published data based on 11 patient weight categories demonstrated lower dose in each patient group achieved with the acquisition protocols developed in our institution. Conclusions: Pediatric CT protocols for 6 patient weight/age-based categories were developed for the whole-body PET/CT. Patientsˈ dose survey demonstrated lower effective CT dose than reported in the literature for each weight category.

Pulmonary angiography with 64-multidetector-row computed tomography in normal dogs.

Pulmonary angiography using 64-multidetector-row computed tomography (MDCT) was used to evaluate pulmonary artery anatomy, and determine the sensitivity of pulmonary artery segment visualization in four Beagle dogs using images reconstructed to 0.625 mm and retro-reconstructed to 1.25 and 2.5 mm slice thickness. Morphologically, characteristic features included a focal narrowing in the right cranial pulmonary artery in all dogs, which should not be mistaken as stenosis. While the right cranial pulmonary artery divided into two equally sized branches that were tracked into the periphery of the lung lobe in all dogs, only a single left cranial (cranial portion) lobar artery was present. Compared with 1.25 and 2.5 mm retro-reconstructions, 0.625 mm reconstructions allowed for detection of significantly (P≤0.05) more pulmonary artery segments and sharper depiction of vessel margins. Clinical applications such as prevalence and significance of diameter changes, and detection of pulmonary arterial thrombembolism on lobar and sublobar level, using pulmonary angiography with 64-MDCT applying 0.625 mm reconstruction slice thickness remain to be established.

Detection of pulmonary embolism using 64-slice multidetector-row computed tomography: accuracy and reproducibility on different image reconstruction parameters

Direct comparison of different image reconstruction parameters to detect pulmonary embolism (PE) using 64-slice multidetector-row computed tomography (MDCT) is absent and the most accurate image reconstruction parameters have not yet been proven. To compare different image reconstruction parameters for detecting PE using 64-slice MDCT in patients suspected of having an acute PE. Forty patients who underwent pulmonary CT angiography with 64-slice MDCT for a suspected PE were included. Different image reconstruction parameters were used for each patient: axial and coronal images with slice thicknesses of 0.625 mm, 1.3 mm, and 2.5 mm and axial maximum intensity projection (MIP) images with slab thicknesses of 1.3 mm, 2.5 mm, and 5 mm. Four experienced radiologists reviewed the images. The diagnosis of a PE was based on consensus review of axial 0.625 mm slice thickness images by two chest radiologists with allowing multiplanar reconstruction. Accuracy and reproducibility (kappa value) were evaluated. In 15 of 40 patients, a PE was diagnosed. For detecting lobar PEs, axial images with a slice thickness of 1.25 mm and all coronal re-formatted images showed comparable results to axial images with a slice thickness of 0.625 mm. For detecting segmental PEs, axial images with a slice thickness of 1.25 mm and coronal images with a slice thickness of 0.625 mm re-formatted images showed comparable results to axial images of a slice thickness of 0.625 mm. For detecting subsegmental PEs, axial images with a slice thickness of 0.625 mm showed the highest sensitivity. Better reproducibility was obtained when the thinner slice thickness reconstructions were in axial and coronal images. However, reproducibility of MIP images with slab thicknesses of 2.5 mm and 5 mm was similar for detecting segmental and subsegmental PEs. Thin-slice reconstruction of less than 1 mm is mandatory for visualization of PE at the subsegmental level.

Year in review 2010: Interstitial lung diseases, acute lung injury, sleep, physiology, imaging, bronchoscopic intervention and lung cancer

Year in review 2010: Interstitial lung diseases, acute lung injury, sleep, physiology, imaging, bronchoscopic intervention and lung cancer

A methodology for direct quantification of over-ranging length in helical computed tomography with real-time dosimetry.

In helical computed tomography (CT), reconstruction information from volumes adjacent to the clinical volume of interest (VOI) is required for proper reconstruction. Previous studies have relied upon either operator console readings or indirect extrapolation of measurements in order to determine the over‐ranging length of a scan.( 1 – 5 ) This paper presents a methodology for the direct quantification of over‐ranging dose contributions using real‐time dosimetry. A Siemens SOMATOM Sensation 16 multislice helical CT scanner is used with a novel real‐time “point” fiber‐optic dosimeter system with 10 ms temporal resolution to measure over‐ranging length, which is also expressed in dose‐length‐product (DLP). (6) Film was used to benchmark the exact length of over‐ranging. Over‐ranging length varied from 4.38 cm at pitch of 0.5 to 6.72 cm at a pitch of 1.5, which corresponds to DLP of 131 to 202 mGy‐cm. The dose‐extrapolation method of Van der Molen et al. yielded results within 3%, while the console reading method of Tzedakis et al.( 2 , 4 ) yielded consistently larger over‐ranging lengths. From film measurements, it was determined that Tzedakis et al.( 2 , 4 ) overestimated over‐ranging lengths by one‐half of beam collimation width. Over‐ranging length measured as a function of reconstruction slice thicknesses produced two linear regions similar to previous publications.( 1 – 4 ) Over‐ranging is quantified with both absolute length and DLP, which contributes about 60 mGy‐cm or about 10% of DLP for a routine abdominal scan. This paper presents a direct physical measurement of over‐ranging length within 10% of previous methodologies.( 1 – 4 ) Current uncertainties are less than 1%, in comparison with 5% in other methodologies. Clinical implantation can be increased by using only one dosimeter if codependence with console readings is acceptable, with an uncertainty of 1.1% This methodology will be applied to different vendors, models, and postprocessing methods – which have been shown to produce over‐ranging lengths differing by 125%. (4) PACS number: 87.57.qp

Dependence of Renal Blood Flow on Renal Artery Stenosis Measured Using CT Angiography

The present study investigates the suitability of computed tomography angiography (CTA) depicting the degree of renal artery stenosis for estimating renal blood flow (RBF) in a kidney. We investigated renal artery stenosis assessment by CTA in eight adult female hybrid pigs with an ultrasound probe implanted at the renal vein for RBF measurement. An inflatable metal-free cuff was placed around the renal artery to control the RBF. The RBF was then reduced in four steps. For each reduced RBF value and baseline RBF, CTA with a reconstructed slice thickness of 0.625 mm was performed in the arterial phase following injection of 80 ml of nonionic intravenous contrast medium. The radius of the stenotic and non-stenotic renal artery segment was measured in the reconstructed images. A significant linear correlation (p < 0.0001) was found between the relative apparent stenosis (calculated as the ratio of the radii of the actual stenotic segment and a non-stenotic renal artery segment) and RBF. The linear regression yielded a slope of 0.57 and a y-axis of 24.1 %. A significant linear correlation (p < 0.0001) was also found between the relative true stenosis (the ratio of the radii of the actual stenotic segment and a non-stenotic renal artery segment at baseline) and the RBF. The linear regression yielded a slope of 0.67 and a y-axis of 13.8 %. The results show that the relative stenosis apparent on CTA differs from the true degree of renal artery stenosis. Nevertheless, the degree of renal artery stenosis determined by CTA provides a reliable estimate of the resulting RBF reduction.

Reproducibility, Accuracy, and Predictors of Accuracy for the Detection of Coronary Atherosclerotic Plaque Composition by Computed Tomography

To determine the reproducibility, accuracy, and predictors of accuracy of computed tomography (CT) angiography to detect and characterize coronary atherosclerotic plaque as compared with intravascular ultrasound. Ten ex vivo human coronary arteries were imaged in a moving phantom by dual-source CT (collimation: 0.6 mm, reconstructed slice thickness: 0.4 mm) and intravascular ultrasound (IVUS). Coregistered cross-sections were assessed at 0.4 mm intervals for the presence and composition of atherosclerotic plaque (noncalcified, mixed, and calcified) on CT and IVUS by independent readers to determine reader agreement and diagnostic accuracy. Quantitative measurements of lumen and plaque area, plaque eccentricity, and intimal thickness on IVUS were used to determine predictors for the detection of noncalcified plaque by CT. Within 1002 coregistered cross-sections, the interobserver agreement to detect plaque on CT was K = 0.48, K = 0.42, and K = 1.00 for noncalcified, mixed, and calcified plaque; respectively. The sensitivity and specificity of CT was 57% out of 84% for noncalcified, 32% of 92% for mixed, and 56% of 93% for calcified plaque when compared with IVUS; respectively. Misclassification occurred in 68% of mixed and 43% of noncalcified plaques. The odds of detecting noncalcified plaque in CT independently increased by 56% (95% CI: 47%-77%, P < 0.0001) with every 0.1 mm increase in maximum intimal thickness as measured by IVUS. Detection rate for noncalcified plaques was poor for plaques <1 mm (36%) but excellent for plaques >1 mm maximal intimal thickness (90%). Reader agreement and diagnostic accuracy for the detection of coronary atherosclerotic plaque vary with plaque composition. Intimal thickness independently predicts detection of noncalcified plaque by CT with excellent sensitivity for >1 mm thick plaques.

The influence of secondary reconstruction slice thickness on NewTom 3G cone beam computed tomography–based radiological interpretation of sheep mandibular condyle fractures

The objective of this study was to examine the diagnostic accuracy of the different secondary reconstruction slice thicknesses of cone beam computed tomography (CBCT) on artificially created mandibular condyle fractures. A total of 63 sheep heads with or without condylar fractures were scanned with a NewTom 3G CBCT scanner. Multiplanar reformatted (MPR) views in 0.2-mm, 1-mm, 2-mm, and 3-mm secondary reconstruction slice thicknesses were evaluated by 7 observers. Inter- and intraobserver agreements were calculated with weighted kappa statistics. The receiver operating characteristic (ROC) curve analysis was used to statistically compare the area under the curve (AUC) of each slice thickness. The kappa coefficients varied from fair and to excellent. The AUCs of 0.2-mm and 1-mm slice thicknesses were found to be significantly higher than those of 2 mm and 3 mm for some type of fractures. CBCT was found to be accurate in detecting all variants of fractures at 0.2 mm and 1 mm. However, 2-mm and 3-mm slices were not suitable to detect fissure, complete, and comminuted types of mandibular condyle fractures.

Does slice thickness affect diagnostic performance of 64-slice CT coronary angiography in stable and unstable angina patients with a positive calcium score?

Coronary calcification can lead to over-estimation of the degree of coronary stenosis. To evaluate whether thinner reconstruction thickness improves the diagnostic performance of 64-slice CT coronary angiography (CTCA) in angina patients with a positive calcium score. We selected 20 scans from a clinical study comparing CTCA to conventional coronary angiography (CCA) in stable and unstable angina patients based on a low number of motion artifacts and a positive calcium score. All images were acquired at 64 x 0.625 mm and each CTCA scan was reconstructed at slice thickness/increment 0.67 mm/0.33 mm, 0.9 mm/0.45 mm, and 1.4 mm/0.7 mm. Two reviewers blinded for CCA results independently evaluated the scans for the presence of significant coronary artery disease (CAD) in three randomly composed series, with > or =2 weeks in between series. The diagnostic performance of CTCA was compared for the different slice thicknesses using a pooled analysis of both reviewers. Significant CAD was defined as >50% diameter narrowing on quantitative CCA. Image noise (standard deviation of CT numbers) was measured in all scans. Inter-observer variability was assessed with kappa. Significant CAD was present in 8% of 304 available segments. Median total Agatston calcium score was 181.8 (interquartile range 34.9-815.6). Sensitivity at 0.67 mm, 0.9 mm, and 1.4 mm slice thickness was 70% (95% confidence interval 57-83%), 74% (62-86%), and 70% (57-83%), respectively. Specificity was 85% (82-88%), 84% (81-87%), and 84% (81-87%), respectively. The positive predictive value was 30 (21-38%), 29 (21-37%), and 28 (20-36%), respectively. The negative predictive value was 97% (95-98%), 97% (96-99%), and 97% (96-99%), respectively. Kappa for inter-observer agreement was 0.56, 0.58, and 0.59. Noise decreased from 32.9 HU at 0.67 mm, to 23.2 HU at 1.4 mm (P<0.001). Diagnostic performance of CTCA in angina patients with a positive calcium score was not markedly affected by modest variations in reconstruction slice thickness.

High diagnostic yield from transbronchial biopsy of solitary pulmonary nodules using low‐dose CT‐guidance

The diagnostic yield from fluoroscopy-guided bronchoscopic transbronchial biopsy of small solitary pulmonary nodules is low. The hypothesis tested in the present study was that the diagnostic yield can be significantly increased by combining flexible bronchoscopy with CT-guidance using a dedicated low-dose protocol. CT-guided transbronchial biopsies were performed in 15 patients with a newly diagnosed solitary peripheral pulmonary nodule and negative conventional bronchoscopic biopsies under fluoroscopic guidance. For imaging, a multi-detector helical CT unit, adjusted at 120 kV, 15 mAs/slice, 4 x 5 mm collimation, 10 mm reconstructed slice thickness and a maximal scan length of 150 mm, was used. After advancing the biopsy forceps towards the lesion, a CT scan was obtained. When the tip of the forceps reached or penetrated the lesion a biopsy was taken, otherwise the procedure was repeated with a maximum of eight attempts. The effective radiation dose was calculated. The average diameter of the nodules was 23 +/- 6 mm (mean +/- SD) with a maximum distance to the parietal pleura of 18 mm (mean 6.5 mm). A mean of 4.1 (range 2-8) CT scans was performed to localize the lesion. In four patients, the forceps only reached the periphery of the nodule. In one patient, the nodule was missed in all attempts. Histology was malignant in eight patients and benign in four patients. In three patients, biopsy results were false negative (benign or non-specific instead of malignant). The overall diagnostic yield was 73%. Complications consisted of two pneumothoraces, one of which necessitated a chest tube. Mean effective radiation dose was 0.55 mSv (range 0.3-1.0). CT-guided transbronchial biopsy can be a valuable diagnostic tool in evaluating solitary pulmonary nodules. This applies for selected patients when other diagnostic methods are either unavailable or inappropriate. The diagnostic yield is high and, when a low-dose protocol is used, radiation exposure can be kept at a minimum.

Influence of slice thickness and reconstruction kernel on the computed tomographic attenuation of coronary atherosclerotic plaque

The computed tomographic (CT) attenuation of coronary atherosclerotic plaque has been proposed as a marker for tissue characterization and may thus potentially contribute to the assessment of plaque instability. We analyzed the influence of reconstruction parameters on CT attenuation measured within noncalcified coronary atherosclerotic lesions. Seventy-two patients were studied by contrast-enhanced dual-source CT coronary angiography (330 millisecond rotation time, 2 x 64 x 0.6 mm collimation, 120 kV, 400 mAs, 80 mL contrast agent intravenously at 6 mL/s), and a total of 100 distinct noncalcified coronary atherosclerotic plaques were identified. Image data sets were reconstructed with a soft (B20f), medium soft (B26f), and sharp (B46f) reconstruction kernel. With the medium soft kernel, image data sets were reconstructed with a slice thickness/increment of 0.6/0.3 mm, 0.75/0.4 mm, and 1.0/0.5mm. Within each plaque, CT attenuation was measured. Mean CT attenuation using the medium soft kernel was 109 +/- 58 HU (range, -16 to 168 HU). Using the soft kernel, mean density was 113 +/- 57 HU (range, -13 to 169 HU), and using a sharp kernel, mean density was 97 +/- 49 HU (range, -23 to 131 HU). Similarly, reconstructed slice thickness had a significant influence on the measured CT attenuation (mean values for medium soft kernel: 102 +/- 52 HU versus 109 +/- 58 HU versus 113 +/- 57 HU for 0.6-mm, 0.75-mm, and 1.0-mm slice thickness). The differences between 0.75-mm and 0.6-mm slice thickness (P = 0.05) and between medium sharp and sharp kernels (P = 0.02) were statistically significant. Image reconstruction significantly influences CT attenuation of noncalcified coronary atherosclerotic plaque. With decreasing spatial resolution (softer kernel or thicker slices), CT attenuation increases significantly. Using absolute CT attenuation values for plaque characterization may therefore be problematic.

Rationality of 16 or more multi-slice helical CT utilization for solitary pulmonary nodule

Objective To analyze the rationality of 16 or more multi-slice helical CT (MSCT) utilization for solitary pulmonary nodule (SPN) (<3 cm). Methods One hundred and fifty consultant cases with SPN from 133 different hospitals, examined with 16 or more MSCT, were selected in this study. The reconstructed slice thickness of routine CT scan, thin slice reconstruction thickness, 2D or 3D reconstruction, window wide and level setting, contrast enhancement effect were recorded from consultant films. Thoracic CT scan criteria for SPN were proposed according to the scan guidelines at Stanford University and PubMed articles. The rationality of 16 or more MSCT utilization in other hospitals for SPN was analyzed by two radiologists compared with scan criteria. The diagnostic accuracy in other hospitals was evaluated according to the pathologic and treatment results in our hospital. Results Sixteen-MSCT was performed in 92 cases, 64-MSCT in 54 cases and 40-MSCT in 4 cases. In routine thoracic CT scan, 9--10 mm reconstructed slice thickness was selected in 59 cases, 7--8 mm thickness in 12 cases and 5 mmthickness in 79 cases. Consecutive thin slice thickness (<3 mm) was used for SPN only in 46 cases. OnlyMPR and VR were filmed in 9 cases without thin slice reconstructed axial images. :53 cases (35.3%) were rescanned in our hospital due to the unsatisfied image quality. Of 150 cases, 78 cases had pathologic or treatment results in our hospital and 22 cases (14.7%) were proved to be misdiagnosed in other hospitals, and only 2 cases were misdiagnosed in our hospital. Conclusion There are many irrationalities of 16 or more MSCT utilization in our country which influence the diagnostic accuracy of SPN, Unified thoracic CT scan criteria in our country are needed. Key words: Coin lesion,pulmonary; Tomography,X-ray computed

Dual-Energy Computed Tomographic Pulmonary Angiography

The aim of this study was to assess if dual-energy computed tomographic pulmonary angiography (DE-CTPA) protocol performed on a dual-source CT scanner can improve image quality and diagnostic confidence compared with 80- and 140-kilovolt (peak) (kVp) image data sets. In an international review board-approved study, 22 patients (women-men, 12:10; mean [SD] age, 58.5 [16.5] years; age range, 18-85 years) underwent DE-CTPA on a dual-source CT for assessing pulmonary embolism. Scan parameters comprised reference milliampere-second of 140 at 140 kVp and 400 at 80 kVp with a pitch of 1.1- and 1.25-mm reconstructed slice thicknesses, respectively. Two radiologists analyzed the 140-kV, 80-kV, and dual-kilovolt images for vessel contrast, subjective image noise, presence of motion, artifacts, and diagnostic confidence at the level of main, lobar, and segmental or subsegmental pulmonary arteries on a 5-point scale (1, uninterpretable; 5, excellent). Computed tomographic numbers and objective noise were measured in these arteries. Data were analyzed using Student t test, Friedman chi2 analysis of variance, and Wilcoxon rank sum test (with Bonferroni correction). At 80 kVp, regardless of motion artifacts, there was a 104% increase in intravascular CT numbers, (mean [SD], 257 [104] Hounsfield units [HU] at 140 kVp and 525 [214] HU at 80 kVp) and 75% increase in objective noise (20 HU at 140 kVp and 35 HU at 80 kVp). Improvement in subjective contrast opacification and CT numbers with 80 kVp compared with 140 kVp was most marked in interlobar, segmental, and subsegmental arteries. Effective radiation dose decrease approximately 28% from a CTDI vol of 26.7 mGy to 20.1 mGy between dual-energy (case) and single-energy (control) groups. In conclusion, DE-CTPA has potential advantages for evaluations of pulmonary embolism and regarding improved image noise, vessel contrast, and diagnostic confidence compared with single higher-kilovolt (peak) protocols.

High-Pitch Electrocardiogram-Triggered Computed Tomography of the Chest

Chest pain is one of the most frequent symptoms in the emergency department. A variety of different diseases, some of them acutely life threatening, can be the underlying cause. Electrocardiogram (ECG)-gated computed tomography angiography of the thorax has been proposed as a cost and time effective imaging technique for these patients. We describe a new high-pitch scan mode, which has been developed specifically for low-dose ECG-triggered computed tomography angiography using dual source computed tomography (CT). Twenty-four patients were examined with this technique on a second generation dual source CT system. The scan mode uses a pitch of 3.2 to acquire a spiral CT data set of the complete thorax in less than 1 second with a temporal resolution of 75 ms (scan parameters: 128 x 0.6 mm collimation, 0.28 seconds gantry rotation time, 370 mAs at 100 kV [15 patients] and 320 mAs at 120 kV [9 patients], reconstructed slice thickness 0.6 mm, increment 0.4 mm). Data acquisition was prospectively triggered at 50% to 60% of the RR interval to cover the range over the heart in diastole. A triple phase contrast injection protocol (total volume: 80 mL) was used to optimize enhancement of the pulmonary and systemic arterial vessels. Image quality was evaluated using a 4-point scale (1 = absence of motion artifacts; 2 = slight motion artifacts, fully evaluable; 3 = motion artifacts, but evaluable; 4 = unevaluable) on a per-segment basis. The patients had an average heart rate of 68 +/- 15 bpm (range: 43-111 bpm) during data acquisition. Motion artifact free visualization of the aorta and pulmonary vessels was possible in each case, of 344 coronary artery segments, 242 (70%) had an image quality score of 1, 60 segments (17%) a score of 2, 28 segments (8%) a score of 3, and 14 segments (4%) were rated as "unevaluable." In 17 patients (10 patients with a heart rate < or =60 bpm) all segments were evaluable. The average dose length product was 113 +/- 11 mGy x cm per scan (mean effective dose 1.6 +/- 0.2 mSv) at 100 kV and 229 +/- 31 mGy x cm per scan (mean effective dose 3.2 +/- 0.4 mSv) at 120 kV. Our initial results indicate that this high-pitch scan mode allows motion artifact free and accurate visualization of the thoracic vessels, and diagnostic image quality of the coronary arteries in patients with low and stable heart rates at a very low radiation exposure.

WE‐C‐BRC‐07: Image Quality QA for Three Radiotherapy Cone‐Beam CT Systems

Purpose: With the increased presence of volumetric radiotherapy cone beam CT (RT‐CBCT) systems, the importance of high grade image quality is crucial to achieve daily image‐guided adaptive radiotherapy (IGART) capabilities. We subjected three commercially available RT‐CBCT systems to a battery of standard diagnostic image quality tests acquired under clinical conditions. This study reports on the evaluation of image qualities for RT‐CBCT's and a diagnostic CT. Methods and Materials: RT‐CBCT scans were performed on Elekta XVI, Nucletron Simulix, and Varian OBI Advanced Imaging using clinical pelvis scan settings on a CATPHAN Model 600. They were then compared to results from a GE Lightspeed CT scanner. The phantom contained modules allowing measurement of low contrast resolution, slice thickness, Hounsfield Unit (HU) sensitivity, spatial resolution, and image uniformity. Results: No CBCT system was able to detect any targets in the low contrast module. Six targets could be seen on diagnostic CT's. All RT‐CBCT systems had greater than 33% variations in slice thickness reconstruction. The HU sensitometry test showed absolute differences between accepted HU values and measured values for XVI and Simulix systems to be on average 6 times and 3 times the error seen in a diagnostic CT respectively. HU sensitivity for OBI is within 15% of a diagnostic CT. Both OBI and Simulix had spatial resolution twice that of XVI but were 3 lp/cm worse than a diagnostic CT. Measurements of image uniformity showed that all three RT‐CBCT systems have a standard deviation of HU values on the order of 10 times that of a diagnostic CT. Conclusions: The image qualities of three evaluated RT‐CBCT systems are relatively comparable, yet still inferior to those from helical CT. It is important to note that dosimetric settings can have a clear impact on image quality, and dose measurements were not done for this work.

TU-D-304A-04: The Influence of CT Resolution On Volume Definition and Image Quality in SRS and SBRT Simulation

Purpose: To determine the influence of resolution of the CT scan (including sub‐millimeter slice thickness) on volume definition and image quality in stereotactic radiotherapy and body radiotherapy simulation. Method and Materials: A novel low‐contrast gel phantom was fabricated with spiculated tumor‐like volumes approximately 2, 5, 8, and 20cc in size. The phantom was scanned using a Philips Brilliance BigBore 16‐slice CT scanner. First, a scan was taken using our standard clinical protocol employing a 16×1.5mm collimator and reconstructed slice thickness of 3mm. Next, a scan was taken with the sub‐millimeter collimator (16×0.75mm) and reconstructed with slice thicknesses of 0.75mm and 3mm for comparison. Contours of the structures were drawn using a specific CT number range in Eclipse. Digitally reconstructed radiographs(DRRs) were exported for evaluating image quality and the standard deviation (SD) was calculated for four uniform, non‐background regions. Results: The difference in measured volume decreased with increasing tumor size when comparing the standard clinical scan and both sub‐millimeter scans. Measured volume varied from 4–16% for volumes less than 10cc when comparing the 0.75mm and clinical scan. The 3mm reconstructed sub‐millimeter scan showed smaller but significant volume differences (>5%). The 16×0.75mm scan increased the CTDIdose by 9.4% versus the clinical protocol scan. Small spicules in the tumors resulted in greater measured volume in the 0.75mm scan. These features were easier to visualize in the 0.75mm DRR, however, SD values were larger than both 3mm scans (15–69%). Conclusion:Tumor size and shape are important considerations in choosing slice thickness for stereotactic radiotherapy simulation. As expected, slice thickness has larger effects on smaller targets. DRR feature sensitivity improved with the 0.75mm scan, but an increase in noise was observed. Our results show that sub‐millimeter slice thickness is useful in SRT for smaller target volumes despite a small increase in patient dose.

Semi-Automated Quantification of Hepatic Lesions in a Phantom

Accurate measurement is crucial for the assessment of tumor dimensions to allow accurate evaluation of tumor response. Thus, the purpose of our study was to assess the accuracy of semi-automated RECIST and volumetric measurements of liver lesions in a liver phantom with different CT acquisition parameters. A phantom of the upper abdomen with 14 hepatic lesions of different sizes (diameter: 12.0-40.0 mm), densities (45/180 HU at 120 kV), or alignment (vertical/transverse) was scanned with a 16-slice multidetector row computed tomography using varying tube currents (40/60/80/100/120/165mAs eff), reconstruction kernels (Siemens B20/30/40/50/70s), or slice thicknesses (1/2/3/4/5 mm). Longest axial diameter and volume of the 14 lesions were quantified using a semi-automated software tool (SyngoOncology, Siemens Medical Solutions, Forchheim, Germany) and compared with the known real longest axial diameter and volume values of the lesions. Absolute percentage errors (APE) were calculated. Degree of agreement in longest axial diameter and volume between software and real measurements was represented graphically in Bland-Altman plots and by corresponding concordance correlation coefficient. At standard soft tissue reconstruction kernel (Siemens B30s) and slice thickness (3 mm) mean absolute percentage error APE (concordance correlation coefficients) ranged between 6.93 and 14.27 (0.96 and 0.99) for longest axial diameter and between 4.98 and 10.85 (0.99 and 1.00) for volume. At varying reconstruction kernels, APE values (concordance correlation coefficients) ranged between 7.92 and 8.31 (0.98 and 0.99) for longest axial diameter and between 4.95 and 6.93 (1.00) for volume. Applying different slice sections APE values (concordance correlation coefficients) differed from 6.54 to 11.82 (0.97 and 0.99) for longest axial diameter and from 6.93 to 9.17 (1.00) for volume. Software quantification of longest axial diameter and volume of hepatic lesions in a phantom demonstrated a high correlation and accuracy under varying multidetector row computed tomography parameter.