Source CT Research Articles

Estimated Radiation Dose Reduction for Prospective Electrocardiography-Triggered Dual Source CT Angiography of the Thoracic Aorta using Iterative Reconstruction: A Prospective Study

Estimated Radiation Dose Reduction for Prospective Electrocardiography-Triggered Dual Source CT Angiography of the Thoracic Aorta using Iterative Reconstruction: A Prospective Study

Frequency split metal artifact reduction (FSMAR) in computed tomography

The problem of metal artifact reduction (MAR) is almost as old as the clinical use of computed tomography itself. When metal implants are present in the field of measurement, severe artifacts degrade the image quality and the diagnostic value of CT images. Up to now, no generally accepted solution to this issue has been found. In this work, a method based on a new MAR concept is presented: frequency split metal artifact reduction (FSMAR). It ensures efficient reduction of metal artifacts at high image quality with enhanced preservation of details close to metal implants. FSMAR combines a raw data inpainting-based MAR method with an image-based frequency split approach. Many typical methods for metal artifact reduction are inpainting-based MAR methods and simply replace unreliable parts of the projection data, for example, by linear interpolation. Frequency split approaches were used in CT, for example, by combining two reconstruction methods in order to reduce cone-beam artifacts. FSMAR combines the high frequencies of an uncorrected image, where all available data were used for the reconstruction with the more reliable low frequencies of an image which was corrected with an inpainting-based MAR method. The algorithm is tested in combination with normalized metal artifact reduction (NMAR) and with a standard inpainting-based MAR approach. NMAR is a more sophisticated inpainting-based MAR method, which introduces less new artifacts which may result from interpolation errors. A quantitative evaluation was performed using the examples of a simulation of the XCAT phantom and a scan of a spine phantom. Further evaluation includes patients with different types of metal implants: hip prostheses, dental fillings, neurocoil, and spine fixation, which were scanned with a modern clinical dual source CT scanner. FSMAR ensures sharp edges and a preservation of anatomical details which is in many cases better than after applying an inpainting-based MAR method only. In contrast to other MAR methods, FSMAR yields images without the usual blurring close to implants. FSMAR should be used together with NMAR, a combination which ensures an accurate correction of both high and low frequencies. The algorithm is computationally inexpensive compared to iterative methods and methods with complex inpainting schemes. No parameters were chosen manually; it is ready for an application in clinical routine.

Coronariografía mediante tomografía computarizada con sincronización prospectiva. Comparación de la calidad de imagen y dosis de radiación con equipos de 128 detectores de fuente única y doble fuente

ObjectiveTo compare the image quality and radiation dose in a group of patients undergoing coronary CT angiography using a 128-slice dual source helical CT scanner with high pitch alto and prospective acquisition with those in a group of patients with similar clinical characteristics undergoing coronary CT angiography using a 128-slice single-source CT scanner with prospective sequential acquisition. Material and methodsWe included 80 patients with heart rates ≤65 beats/min: 40 underwent sequential 128-slice single source CT with prospective synchronization and the other 40 underwent 128-slice dual source helical CT with high pitch and prospective synchronization. Two radiologists independently assessed the quality of the images of the coronary arteries on the 80 coronary CT angiograms: image quality was classified on a four-point scale in which 1 represented excellent and 4 deficient. The effective dose of radiation was also calculated. ResultsThe clinical characteristics of the patients in the two groups were similar. The image quality obtained with dual source CT was significantly better than that obtained with single source CT (P=0.006). The mean effective dose of radiation in the group undergoing dual source CT was 36% lower than in the group undergoing single source CT (1.4±0.6 mSv vs. 2.2±0.9 mSv; P<0.01). ConclusionAlthough both sequential 128-slice single source CT with prospective acquisition and 128-slice dual source helical CT with high pitch and prospective acquisition provide good image quality and low effective doses of radiation, 128-slice dual source helical CT with prospective acquisition provides better image quality and results in a lower effective dose of radiation.

CT-angiography before TAVI using high-pitch spiral acquisition mode

Preparation for transcatheter aortic valve implantation (TAVI) requires imaging of the aortic root, aorta, and iliac arteries. Contrast agent exposure can be a problem in TAVI candidates who often have impaired renal function. High-pitch spiral CT allows high-resolution imaging of large volumes in a very short time. We evaluated the ability of high-pitch spiral imaging with dual source CT (“Flash Mode”) and a minimized amount of intravenous contrast to evaluate aortic root anatomy and suitability of vascular access for TAVI procedures.

Routine chest and abdominal high-pitch CT: An alternative low dose protocol with preserved image quality

To investigate the radiation dose and image quality of the high-pitch dual source computer tomography (DSCT) for routine chest and abdominal scans. 130 consecutive patients (62 female, 68 male, median age 55 years) were included. All patients underwent 128-slice high-pitch DSCT (chest n=99; abdomen n=84) at a pitch of 3.2. Two observers independently rated image quality using a 4-point score (1: excellent to 4: non-diagnostic). Image noise was measured and operational radiation dose quantities were recorded. An additional group of 132 patients (chest, n=80; abdomen n=52) scanned with standard-pitch CT matched for age, gender, and body mass index (BMI) served as control group. Interobserver agreement for image quality rating was good (k=0.74). Subjective image quality of high-pitch CT was diagnostic in all patients (median score chest; 2, median score abdomen: 2). Image noise of high-pitch CT was comparable to standard-pitch for the chest (p=0.32) but increased in the abdomen (p<0.0001). For high-pitch CT radiation dose was 4.4±0.9 mSv (chest) and 6.5±1.2 mSv (abdomen). These values were significantly lower compared to standard-pitch CT (chest: 5.5±1.2 mSv; abdomen: 11.3±3.8 mSv). Based on the technical background high-pitch dual source CT may serve as an alternative scan mode for low radiation dose routine chest and abdominal CT.

Radiation Dose Reduction of Chest CT with Iterative Reconstruction in Image Space - Part I: Studies on Image Quality Using Dual Source CT

ObjectiveTo determine whether the image quality (IQ) is improved with iterative reconstruction in image space (IRIS), and whether IRIS can be used for radiation reduction in chest CT.Materials and MethodsStandard dose chest CT (SDCT) in 50 patients and low dose chest CT (LDCT) in another 50 patients were performed, using a dual-source CT, with 120 kVp and same reference mAs (50 mAs for SDCT and 25 mAs for LDCT) employed to both tubes by modifying a dual-energy scan mode. Full-dose data were obtained by combining the data from both tubes and half-dose data were separated from a single tube. These were reconstructed by using a filtered back projection (FBP) and IRIS: full-dose FBP (F-FBP); full-dose IRIS (F-IRIS); half-dose FBP (H-FBP) and half-dose IRIS (H-IRIS). Objective noise was measured. The subjective IQ was evaluated by radiologists for the followings: noise, contrast and sharpness of mediastinum and lung.ResultsObjective noise was significantly lower in H-IRIS than in F-FBP (p < 0.01). In both SDCT and LDCT, the IQ scores were highest in F-IRIS, followed by F-FBP, H-IRIS and H-FBP, except those for sharpness of mediastinum, which tended to be higher in FBP. When comparing CT images between the same dose and different reconstruction (F-IRIS/F-FBP and H-IRIS/H-FBP) algorithms, scores tended to be higher in IRIS than in FBP, being more distinct in half-dose images. However, despite the use of IRIS, the scores were lower in H-IRIS than in F-FBP.ConclusionIRIS generally helps improve the IQ, being more distinct at the reduced radiation. However, reduced radiation by half results in IQ decrease even when using IRIS in chest CT.

Radiation Dose Reduction of Chest CT with Iterative Reconstruction in Image Space - Part II: Assessment of Radiologists' Preferences Using Dual Source CT

ObjectiveTo evaluate the impact of radiation dose and reconstruction algorithms on radiologists' preferences, and whether an iterative reconstruction in image space (IRIS) can be used for dose reduction in chest CT.Materials and MethodsStandard dose chest CT (SDCT) in 50 patients and low dose chest CT (LDCT) in another 50 patients were performed, using a dual-source CT, with 120 kVp and same reference mAs (50 mAs for SDCT and 25 mAs for LDCT) employed to both tubes by modifying the dual-energy scan mode. Full-dose data were obtained by combining the data from both tubes and half-dose data were separated from one tube. These were reconstructed by using a filtered back projection (FBP) and IRIS: full-dose FBP (F-FBP); full-dose IRIS (F-IRIS); half-dose FBP (H-FBP) and half-dose IRIS (H-IRIS). Ten H-IRIS/F-IRIS, 10 H-FBP/H-IRIS, 40 F-FBP/F-IRIS and 40 F-FBP/H-IRIS pairs of each SDCT and LDCT were randomized. The preference for clinical usage was determined by two radiologists with a 5-point-scale system for the followings: noise, contrast, and sharpness of mediastinum and lung.ResultsRadiologists preferred IRIS over FBP images in the same radiation dose for the evaluation of the lungs in both SDCT (p = 0.035) and LDCT (p < 0.001). When comparing between H-IRIS and F-IRIS, decreased radiation resulted in decreased preference. Observers preferred H-IRIS over F-FBP for the lungs in both SDCT and LDCT, even with reduced radiation dose by half in IRIS image (p < 0.05).ConclusionRadiologists' preference may be influenced by both radiation dose and reconstruction algorithm. According to our preliminary results, dose reduction at 50% with IRIS may be feasible for lung parenchymal evaluation.

X-ray induced DNA double-strand breaks in coronary CT angiography: Comparison of sequential, low-pitch helical and high-pitch helical data acquisition

Aim of this study was to compare DNA double-strand breaks (DSBs) in blood lymphocytes of patients undergoing high-pitch helical, low-pitch helical and sequential coronary CT angiography. 66 patients were examined with various scan protocols and modes (low-pitch helical scan: 100-120 kV, 320-438 mAs/rot, pitch 0.18-0.39, with or without ECG-pulsing, n=35; prospectively ECG-triggered high-pitch helical scan: 100-120 kV, 320-456 mAs/rotation, pitch 3.2-3.4, n=19; prospectively ECG-triggered sequential scan: 100-120 kV, 150-300 mAs or 320-370 mAs/rotation, n=12) either using a 64-slice or 128-slice dual-source CT or a 128-slice single source CT scanner. Blood samples were obtained before and 30 min after CT and DSBs were analyzed in isolated lymphocytes using γ-H2AX immunofluorescence microscopy. A significant increase of DSBs was measurable 30 min after CTA (range 0.01-0.71/cell). CT induced DSBs showed a significant correlation with the estimated effective dose (ρ=0.90, p<0.00001). Both prospectively ECG-triggered sequential (0.10 DSBs/cell, 176 mGy cm, p<0.00001) and high-pitch helical scan protocols (0.03 DSBs/cell, 109 mGy cm, p<0.00001) led to a significant reduction of median DLP and DSB levels compared to low-pitch helical scans (0.34 DSBs/cell, 828 mGy cm). A reduction of the tube voltage resulted in significantly lower whereas additional calcium scoring resulted in elevated DLP and DNA damages (p<0.05 each). In coronary CTA, data acquisition protocols have a significant influence on the X-ray induced DSB levels. Using γ-H2AX immunofluorescence microscopy different scan modes in different CT generations can be compared concerning their biological impact.

Abstract 17754: Accuracy of Dual Source Computed Tomography to Predict Suitable Angulations for Fluoroscopic Guidance During Transcatheter Aortic Valve Implantation (TAVI)

For Transcatheter Aortic Valve Implantation (TAVI), optimal selection of fluoroscopic projections is important and often requires multiple aortic angiograms in various angulations. We analyzed the ability of Dual Source CT (DSCT) to predict suitable angulations for fluoroscopy during the TAVI procedure, including influence on procedural parameters and contrast use. Methods: 75 consecutive patients who underwent TAVI using the Edwards-Sapien valve were evaluated. Possible angulations which would render an orthogonal view onto the aortic valve plane were determined by interactive evaluation of pre_procedural contrast-enhanced DSCT data sets acquired during i.v. injection of 40ml contrast agent. TAVI operators used a predicted angulation for the first aortic angiogram and performed additional aortic angiograms if no satisfactory view of the valve plane was obtained. Predicted angulations were compared to the angulation used for valve implantation. Differences of less than 5° (sum of LAO-RAO and CRAN-CAUD deviation) were considered as accurate prediction. Radiation exposure and contrast use was compared between patients with accurate prediction of fluoroscopic angulations by CT versus those in whom CT failed to predict a suitable view. Aortic valve calcifum was visually quantified in CT as mild, moderate, severe. Results: TAVI was successful in all 75 patients. The mean difference between the CT-predicted angulation and the angulation used for implantation was 3±6°. CT predicted a suitable angulation in 63/75 cases (84%). The number of aortic angiograms acquired in patients with correct prediction (1.02±0.1) was lower than in patients with incorrect prediction (3.0±1.7, p &lt; 0.001). Similarly, the amount of contrast agent required for the entire TAVI procedure was lower in patients with correct prediction (72±36ml vs. 106±39 ml, p = 0.001). Extensive calcifications of the aortic valve were associated with a lower frequency of correct prediction (100% for mild, 89% for moderate, and 71% for severe calcification, p = 0.03). Conclusion: CT allows prediction of suitable fluoroscopy angulations during TAVI in the majority of cases, which significantly reduces the required amount of contrast.

Application of double source multidetector computed tomography in visualization of cardiac veins

To evaluate the value of double source multidetector computed tomography (MDCT) in visualization of cardiac veins in patients with chronic heart failure. Thirty-five patients with chronic heart failure (aged 65.4 ± 8.8, 21 males and 14 females) were enrolled in the study. In Group A, MDCT and retrograde coronary venography (RCV) were performed consecutively; in Group B anterograde visualization of the coronary venous and RCV were performed. Coronary sinus, GCV and MCV of all individuals were identified in MDCT. LVPV was observed in 65% patients of Group A, and 66.7% patients of Group B. The correlation coefficient between MDCT and RCV was 0.944, and that between CVG and RCV was 0.42. Non-invasive evaluation of cardiac veins with double source CT is feasible and may be used in cardiac resynchronization therapy.

Reduced Radiation Dose of Thoracic and Cardiac Dual Source Computertomography with High-Pitch Protocol in Infants and Children

Objectives: To investigate the feasibility and the image quality of thoracic and cardiac dual source CT (DSCT) with ultra-low radiation in infants and young children without sedation.

Automatic Acquisition of the Four-Chamber View of Heart from Dual Source CT Data

The four-chamber view of heart plays an important role in clinical diagnosis of cardiac disease. According to the geometric structure of heart, we propose a method to automatic acquisition of the four-chamber view in volume data. First, the contrast-medium enhanced part of dual source CT data is segmented and morphological operations are applied. Second, the Dijkstra Algorithm considering 3D Euler Distance as weighting factor is introduced to extract the center line of atrium and ventricle. Finally, the four-chamber view of heart is estimated based on the 3D Euclidean Distance and the geometric characteristics of the center line. In this paper, 40 patients (age from 49 to 81) are examined, and the recognition rate is 91.25%.

Automated bone removal in CT angiography: Comparison of methods based on single energy and dual energy scans

To evaluate dual energy based methods for bone removal in computed tomography angiography (CTA) images and compare these with single energy based methods that use an additional, nonenhanced, CT scan. Four different bone removal methods were applied to CT scans of an anthropomorphic thorax phantom, acquired with a second generation dual source CT scanner. The methods differed by the way information on the presence of bone was obtained (either by using an additional, nonenhanced scan or by scanning with two tube voltages at the same time) and by the way the bone was removed from the CTA images (either by masking or subtracting the bone). The phantom contained parts which mimic vessels of various diameters in direct contact with bone. Both a quantitative and qualitative analysis of image quality after bone removal was performed. Image quality was quantified by the contrast-to-noise ratio (CNR) normalized to the square root of the dose (CNRD). At locations where vessels touch bone, the quality of the bone removal and the vessel preservation were visually assessed. The dual energy based methods were assessed with and without the addition of a 0.4 mm tin filter to the high voltage x-ray tube filtration. For each bone removal method, the dose required to obtain a certain CNR after bone removal was compared with the dose of a reference scan with the same CNR but without automated bone removal. The CNRD value of the reference scan was maximized by choosing the lowest tube voltage available. All methods removed the bone completely. CNRD values were higher for the masking based methods than for the subtraction based methods. Single energy based methods had a higher CNRD value than the corresponding dual energy based methods. For the subtraction based dual energy method, tin filtration improved the CNRD value with approximately 50%. For the masking based dual energy method, it was easier to differentiate between iodine and bone when tin filtration was applied. The CNRD value decreased only with 4% in that case. Compared to the dual scan based methods, the dual energy based methods had the advantage that only a single scan was made without the need of image registration. This might be easier to implement in clinical practice. Vessel preservation was better with bone subtraction than with bone masking. Smaller vessels were completely occluded by the bone mask. None of the bone removal methods was dose neutral. In general, dual scan based methods that use the lowest tube voltage available, have a higher CNR than the dual energy based approaches at the same dose level. Tin filtration improves the ability to differentiate between iodine and bone for the dual energy based masking method. In clinical practice, the advantages of the dual energy masking method might outweigh its disadvantage of a slightly higher dose penalty compared to the conventional dual scan masking method.

Contrast material injection protocol with the flow rate adjusted to the heart rate for dual source CT coronary angiography

To investigate the effect on coronary arterial attenuations of contrast material flow rate adjusted to a patient's heart rate during dual source CT coronary angiography (DSCT-CCTA). A total of 296 consecutive patients (mean age: 58.7 years) undergoing DSCT-CCTA without previous coronary stent placement, bypass surgery, congenital or valvular heart disease were included. The image acquisition protocol was standardized (120 kV, 380 mAs) and retrospective electrocardiograph (ECG) gating was used. Patients were randomly assigned to one of three groups [flow rate: G1: dosage/16, G2: dosage/(scan time +8), G3: fixed flow rate]. The groups were compared with respect to the attenuations of the ascending aorta (AA) above coronary ostia, the left main coronary artery (LM), the proximal right coronary artery (RCA), the left anterior descending artery (LAD), the left circumflex artery (LCX), and the contrast to noise ratio of the LM (LM(CNR)) and the proximal RCA (RCA(CNR)). Correlations between heart rate and attenuation of the coronary arteries were evaluated in three groups with linear regression. There was no significant difference in the three groups among the mean attenuations of AA (P = 0.141), LM (P = 0.068), RCA (P = 0.284), LM(CNR) (P = 0.598) and RCA(CNR) (P = 0.546). The attenuations of the LAD and the LCX in group 1 were slightly higher than those in group 2 and 3 (P < 0.05). In group 1, the attenuations of the AA (P < 0.01), LM (P < 0.01), RCA (P < 0.01), LAD (P = 0.02) and LCX (P < 0.01) decreased, respectively, with an increasing heart rate. A similar finding was detected in group 3 (AA: P < 0.01, LM: P < 0.01, RCA: P < 0.01, LAD: P < 0.01 and LCX: P < 0.01). In contrast, the attenuations of the AA (P = 0.55), LM (P = 0.27), RCA (P = 0.77), LAD (P = 0.22) and LCX (P = 0.74) had no significant correlation with heart rate in group 2. In all three groups, LM(CNR) (P = 0.77, 0.69 and 0.73 respectively) and RCA(CNR) (P = 0.75, 0.39 and 0.61 respectively) had no significant correlation with heart rate. Contrast material flow rate adjusted to heart rate can diminish the influence of heart rate on attenuations of the coronary arteries in DSCT-CCTA.

The relationship studies between the profiling of blood biomarker and the CT imaging characteristics on coronary atherosclerosis

Background and ObjectiveStudies showed that the metabolic disorder of lipid and inflammatory factor in blood might lead to the injury of endothelium, and then generate artherosclerosis gradually. It is difficult...

Comparison of image quality and radiation dose of different pulmonary CTA protocols on a 128-slice CT: high-pitch dual source CT, dual energy CT and conventional spiral CT

To compare image quality and radiation dose of high-pitch dual-source computed tomography (DSCT), dual energy CT (DECT) and conventional single-source spiral CT (SCT) for pulmonary CT angiography (CTA) on a 128-slice CT system. Pulmonary CTA was performed with five protocols: high-pitch DSCT (100 kV), high-pitch DSCT (120 kV), DECT (100/140 kV), SCT (100 kV), and SCT (120 kV). For each protocol, 30 sex, age, and body-mass-index (mean 25.3 kg/m(2)) matched patients were identified. Retrospectively, two observers subjectively assessed image quality, measured CT attenuation (HU±SD) at seven central and peripheral levels, and calculated signal-to-noise-ratio (SNR) and contrast-to-noise-ratio (CNR). Radiation exposure parameters (CTDIvol and DLP) were compared. Subjective image quality was rated good to excellent in >92% (>138/150) with an interobserver agreement of 91.4%. The five protocols did not significantly differ in image quality, neither by subjective, nor by objective measures (SNR, CNR). By contrast, radiation exposure differed between protocols: significant lower radiation was achieved by using high-pitch DSCT at 100 kV (p < 0.01 in all). Radiation exposure of DECT was in between SCT at 100 kV and 120 kV. SCT, high-pitch DSCT, and DECT protocols techniques result in similar subjective and objective image quality, but radiation exposure was significantly lower with high-pitch DSCT at 100 kV. New CT protocols show promising results in pulmonary embolism assessment. High-pitch dual-source CT (DSCT) at 100 kV provides radiation dose savings for pulmonary CTA. High-pitch DSCT at 100 kV maintains diagnostic image quality for pulmonary CTA. Dual energy CT uses more radiation but also provides lung perfusion evaluation. Whether the additional perfusion data is worth the extra radiation remains undetermined.

Dynamic CT technique for assessment of wrist joint instabilities

To develop a 4D [three-dimensional (3D) + time] CT technique to capture high spatial and temporal resolution images of wrist joint motion so that dynamic joint instabilities can be detected before the development of static joint instability and onset of osteoarthritis (OA). A cadaveric wrist was mounted onto a custom motion simulator and scanned with a dual source CT scanner during radial-ulnar deviation. A dynamic 4D CT technique was utilized to reconstruct images at 20 equidistant time points from one motion cycle. 3D images of carpal bones were generated using volume rendering techniques (VRT) at each of the 20 time points and then 4D movies were generated to depict the dynamic joint motion. The same cadaveric wrist was also scanned after cutting all portions of the scapholunate interosseus ligament to simulate scapholunate joint instability. Image quality were assessed on an ordinal scale (1-4, 4 being excellent) by three experienced orthopedic surgeons (specialized in hand surgery) by scoring 2D axial images. Dynamic instability was evaluated by the same surgeons by comparing the two 4D movies of joint motion. Finally, dose reduction was investigated using the cadaveric wrist by scanning at different dose levels to determine the lowest radiation dose that did not substantially alter diagnostic image quality. The mean image quality scores for dynamic and static CT images were 3.7 and 4.0, respectively. The carpal bones, distal radius and ulna, and joint spaces were clearly delineated in the 3D VRT images, without motion blurring or banding artifacts, at all time points during the motion cycle. Appropriate viewing angles could be interactively selected to view any articulating structure using different 3D processing techniques. The motion of each carpal bone and the relative motion among the carpal bones were easily observed in the 4D movies. Joint instability was correctly and easily detected in the scan performed after the ligament was cut by observing the relative motion between the scaphoid and lunate bones. Diagnostic capability was not sacrificed with a volume CT dose index (CTDI(vol)) as low as 18 mGy for the whole scan, with estimated skin dose of approximately 33 mGy, which is much lower than the threshold for transient skin erythema (2000 mGy). The proposed dynamic 4D CT imaging technique generated high spatial and high temporal resolution images without requiring periodic joint motion. Preliminary results from this cadaveric study demonstrate the feasibility of detecting joint instability using this technique.

SU‐E‐I‐10: Skin Dose in Routine CT Brain Perfusion Studies Using Siemens 64 Slice, Definition Dual Source, and Flash CT Scanners

Purpose: To determine and compare the entrance skin doses from the routine CT brain perfusion protocols on various Siemens CT scanners. Methods: Four Siemens CT scanners were surveyed using their brain perfusion protocol (see supporting document): two Sensation 64‐slice scanners (EC‐CT‐2 and IP‐CT‐2), one Definition Dual Source (64‐slice), and one Definition Flash (128‐slice). The skin dose was measured using a RANDO® anthropomorphic phantom and Landauer optically stimulated luminescent (OSL) nanoDot dosimeters. We performed the scan three times on each scanner with the OSL nanoDots on the surface of the head at the 0, 90, 180, and 270 degree positions. We then averaged the skin doses from the three scans at each of the four positions to calculate an average skin dose for each CT scanner and an average skin dose per scan, independent of position. Results: The mean skin doses obtained were 341.7 mGy ± 44.5 for the Definition Dual Source, 326.7 mGy ± 37.3 for EC‐CT‐2 (64 slice), 326.6 mGy ± 55.6 for IP‐CT‐2 (64 slice), and 435.6 mGy ± 29.7 mGy for the Flash CT. The skin doses of the two 64‐slice scanners and the Definition dual source CT were similar, as expected, since they employed the same beam width. The skin dose of the Flash CT was 32.8% higher, which as expected, since its beam width is ∼33% larger (38.4 mm for the Flash vs. 28.8 mm for the others). Conclusions: Based on the phantom study, the skin doses for routine CT brain perfusion protocols on the mentioned scanners are 325–435 mGy, which is far below the dose threshold for possible radiation induced skin damage (2000 mGy)

SU‐E‐I‐11: Extraction of Blood Flow Patterns and Calculation of Heart function Parameters in Dual Source CT Angiography

Purpose: A new approach is presented to extract the coronary artery blood flow patterns from the angiographic data and to calculate the parameter to evaluate the heart function. Methods: This method uses five patientsˈ coronary angiographic data. Firstly, use a ˈseedˈ method to extract the coronary artery in a completely automatic way. Secondly, acquire the blood flow patterns from the angiographic data with a ‘dynamic registration’ method and save the result image sequence as an AVI file. Finally, calculate the heart function parameter (velocity of blood flow) by frame counting method. Results: The accurate boundary of the coronary artery and the blood flow is clearly presented, and the velocity of blood flow is similar to the Dopller ultrasound measurement. Conclusions: This method is shown with good performance, particularly in modeling the blood flow patterns and calculation of heart function parameter. It provides not only an automatic, fast, real‐time and accurate method in precise diagnosis and treatment of coronary disease, but also a complementary criterion to evaluate the heart function, and then predict the recovery.

111 Single centre prospective cardiac CT study to determine the prevalence of patients with coronary artery disease with a zero coronary artery calcium score and associated non-cardiac incidental findings

<h3>Introduction</h3> Cardiac CT, incorporating coronary artery calcium (CAC) scoring and angiography, is being increasingly used to evaluate patients with chest pain and exclude coronary artery disease (CAD), as recommended in the recent NICE guidelines. Calcification of the coronary arteries is an excellent marker of underlying atherosclerosis, but a zero CAC score does not completely exclude the diagnosis as potentially significant non-calcified plaques will not be detected by CAC scoring. CT imaging may also identify non-cardiac incidental findings that can lead to further downstream testing and medical expense. <h3>Objectives</h3> (1) To evaluate the probability of CAD in patients with a CAC score of zero. (2) To determine the incidence of non-cardiac incidental findings on cardiac CT and to quantify resulting investigations. <h3>Methods</h3> 116 symptomatic patients undergoing cardiac CT to exclude CAD from November 2009 to October 2010 were prospectively enrolled. Patients underwent CAC scoring and had contrast-enhanced, 128-slice, dual source CT coronary angiography (CTCA―Siemens Flash). Scans were dual-reported by a cardiac radiologist and a cardiologist. Statistical analysis was performed using GraphPadPrism. <h3>Results</h3> 62/116 patients had a CAC score of zero. Of these, 57 (91.9%) patients had normal coronary arteries, 4 (6.5%) patients had non-obstructive CAD (stenosis &lt;50%), and 1 patient (1.6%) had significant obstructive CAD (stenosis&gt;50%). This patient with obstructive CAD had a high grade lesion in the proximal left anterior descending artery that required intervention. 54/116 had non-zero CAC scores. Of these, 13 (24%) had obstructive CAD and 41 (76%) non-obstructive CAD. 42/116 (36%) patients had incidental findings on cardiac CT that are summarised in Abstract 111 table 1. These incidental findings resulted in further investigations, documented in Abstract 111 table 2. The mean radiation dose (± SEM) for CAC scoring was 0.61±0.03 mSv. The mean radiation dose (± SEM) for subsequent CTCA was 2.66 ± 0.32 mSv in high pitch “flash” mode (n=27), 5.86±0.50 mSv in prospective mode (n=64) and 17.15±1.68 mSv in the retrospective mode (n=25). <h3>Conclusions</h3> Despite 62 patients having a reassuring CAC score of zero, 8% of this group had evidence of non-calcified plaque, with one patient having obstructive CAD that required intervention. We conclude that if strong clinical suspicion remains in patients with a CAC score of zero further coronary investigation may be warranted. Incidental findings are common, and can result in multiple further investigations for patients. Further research is needed to evaluate the added cost, clinical benefits and radiation exposure created by investigation of such incidental findings in the context of cardiac CT.