Prospective Gating Research Articles

Intraindividual comparison of image quality using retrospective and prospective respiratory gating for the acquisition of thin sliced four dimensional multidetector CT of the thorax in a porcine model

ABSTRACTPurpose: To intraindividually compare image quality and anatomical depiction of the lung and mediastinum using retrospective and prospective respiratory gating techniques for the acquisition of 4D-multidetector computed tomography (MDCT) of the chest in a porcine model. Materials and Methods: Twelve trachealy intubated domestic pigs underwent 64-row MDCT of the thorax. For retrospective and prospective gating the automated respiratory frequency was adjusted to 10, 14, 18, and 22 respiratory cycles per minute. Further, free breathing MDCT scans of the lung were performed at the same respiratory settings. A breathhold scan was acquired which served as the reference standard. Three reviewers independently analyzed the MDCT data applying a 4-point-grading scale regarding the degree of artifacts observed and anatomical depiction (1, excellent, no artifacts; 4, nondiagnostic due to severe artifacts). For statistical analysis the Wilcoxon matched pairs and Chi-square test were used. Results: Breathhold imaging allowed for the highest image quality (mean value: trachea, 1.00; bronchi, 1.10; lung parenchyma, 1.08; diaphragm, 1.00; pericardium, 1.80). Retrospective gating proved to be of superior image quality compared to prospective gating for all respiratory frequencies. With the respiratory frequency set to 14/min retrospective gating even enabled an identical image quality score as at breathhold. Performing image acquisition during continuous breathing lead to a severe decrease in image quality. Conclusions: High image quality can be acquired using respiratory gating techniques for 4D-MDCT of the thorax. Retrospective is superior to prospective gating and can be of an equivalent image quality as standard breathhold imaging, but at the cost of a significantly higher radiation dose.

Abstract 175: Dual source 128-slice computed tomography coronary angiography: A low radiation paradigm in evaluation of Kawasaki disease at Chandigarh, North India

Objective: To evaluate the feasibility of low dose computed tomography coronary angiography (CTCA) on a dual source scanner in children on follow up for Kawasaki disease (KD). Methods: A prospective study comprising 20 consecutive children with KD was conducted from November 2013 to August 2014 on 128-dual source second generation Siemens Definition Flash with either prospective or retrospective electrocardiographic (ECG) gating. A radiologist blinded to the clinical profile and echocardiography (ECHO)/ stress thallium data evaluated each scan. Peak Kilovolts (KVp), milliampere (mA) and radiation dose (dose length product-mGycm and effective dose milliSieverts-mSv) were recorded. Another radiologist correlated CTCA data with clinical/ other imaging data. Results: Demographic/ clinical data and scan parameters are given in Table. Mean effective dose was 1.25 mSv (range 0.22 to 2.74), with prospective ECG gating in 8 patients, it was even lower (0.22 to 0.91 mSv). Six of the 20 patients showed abnormalities including ectasia (n=3), aneurysm (n=2) and stenosis (n=3). More than one abnormality was seen in 2 patients. Four children with normal ECHO had abnormalities detected on CTCA. Stress thallium scintiscan had been performed in 16 patients with mild/ moderate reversible perfusion defects detected in 14. Six of 14 patients with moderate perfusion abnormalities had an abnormal CTCA. Conclusion: In our experience, dual source CTCA is a feasible low radiation dose modality in evaluation in patients with KD. Future impact: Dual source CTCA has potential to be standard of care for evaluation of coronary artery abnormalities in KD.

Objective and subjective image quality with prospectively gated versus ECG-controlled tube current modulation using 256-slice computed tomographic angiography

IntroductionRadiation exposure is one of the major limitations of computed tomographic coronary angiography (CTA). The purpose of this study was to compare the objective and subjective image quality and radiation dose using prospective ECG gating (PGA) versus ECG-controlled tube current modulation (ECTCM) scanning techniques. MethodsA prospective, single-center study was performed at Prince Sultan Cardiac Centre, Qassim, Saudi Arabia. A total of 104 patients with low-to- intermediate probability of coronary artery disease (CAD) underwent CTA with either PGA or ECTCM acquisition. PGA was performed during the study period and compared with the last 50 CTAs previously done using ECTCM. A 4-point scale was used to assess the image quality subjectively. Objective image quality was assessed using image signal, noise, and signal-to-noise ratio (SNR). ResultsPatient‘s Baseline characteristics were not different between the two scanning protocols. The 4-point score of subjective image quality showed no significant differences between the PGA and ECTCM scans (2.9±0.7, 2.96±0.7, respectively; p=0.87). The objective image quality showed significantly higher noise and lower SNR with PGA compared with ECTCM (31±9, 27±9, respectively; p<0.001 for noise) and (15±5, 17±7, respectively; p<0.001 for SNR), with no statistical difference in the image signal (434±123, 425±103 HU, respectively, p=0.7).Radiation exposure was significantly lower with PGA than with ECTCM. The dose-length product (DLP) for PGA was 334±130mGy, compared with 822±286mGy for the ECTCM. This corresponds to a 59% reduction in radiation exposure (p<0.0001). ConclusionsAlthough prospective ECG-triggered axial scanning increased image noise, it maintained subjective image quality and was associated with a 59% reduction in radiation exposure when compared with ECTCM.

The influence of novel CT reconstruction technique and ECG-gated technique on image quality and patient dose of cardiac computed tomography.

The aim of the present study was to compare image quality and patient dose in cardiac computed tomography angiography (CTA) in terms of volume computed tomography dose index (CTDI vol), dose length product (DLP) and effective dose, when changing from filtered back projection (FBP) to adaptive iterative dose reduction (AIDR) reconstruction techniques. Further aim was to implement prospective electrocardiogram (ECG) gating for patient dose reduction. The study was performed with Aquilion ONE 320-row CT of Toshiba Medical Systems. Analysis of cardiac CT protocols was performed before and after integration of the new software. The AIDR technique showed more than 50 % reduction in CTDIvol values and 57 % in effective dose. The subjective evaluation of clinical images confirmed the adequate image quality acquired by the AIDR technique. The preliminary results indicated significant dose reduction when using prospective ECG gating by keeping the adequate diagnostic quality of clinical images.

The use of a generalized reconstruction by inversion of coupled systems (GRICS) approach for generic respiratory motion correction in PET/MR imaging

Respiratory motion is a source of artifacts in multimodality imaging such as PET/MR. Solutions include retrospective or prospective gating. They have however found limited use in clinical practice, since their increased overall acquisition duration to maintain overall image quality. More elaborate methods consist of using 4D MR datasets to extract spatial deformations in order to correct for the respiratory motion in PET. The main drawbacks of such approaches is the relatively long acquisition times associated with 4D MR imaging which is often incompatible with clinical PET/MR protocols. The objective of this work was to overcome these limitations by exploiting a generalized reconstruction by inversion of coupled systems (GRICS) approach. The methodology is based on a joint estimation of motion during the MR image reconstruction process, providing internal structure motion and associated deformation matrices for retrospective use in PET respiratory motion correction. This method was first validated on four MR volunteers and two PET/MR patient datasets by comparing GRICS generated MR images to 4D MR series obtained by retrospective gating. In a second step 4D PET datasets corresponding to acquired 4D MR images were simulated using the GATE Monte Carlo simulation platform. GRICS generated deformation matrices were subsequently used to correct respiratory motion in comparison to the 4D MR image based deformations both for the simulated and the two 4D PET/MR patient datasets. Results confirm that GRICS synchronized MR images correlate well with the acquired 4D MR series. Similarly, the use of GRICS for respiratory motion correction allows an equivalent percentage improvement on lesion contrast, position and size, considering the PET simulated tumors as well as PET real tumors. This work demonstrates the potential interest of using GRICS for PET respiratory motion correction in combined PET/MR using shorter duration acquisitions without the need for 4D MRI and associated specific MR sequences.

The effect of respiratory gating strategy on left ventricular cardiac strains with DENSE

Background Displacement Encoding with Stimulated Echoes (DENSE) directly measures tissue displacements and can be used to quantify cardiac mechanics. Multi-dimensional DENSE results in lengthy scans that require respiratory gating, acquiring data only while the diaphragm is within a prespecified “acceptance window.” Because it is not possible to perform respiratory gating during data acquisition, DENSE can employ the following respiratory gating strategies: 1) acquire data and keep it if the diaphragm is inside the window after acquisition (retrospective) 2) acquire data and keep it only if the diaphragm was inside the window right before data acquisition (prospective) or 3) a combination of retrospective and prospective where the diaphragm must be inside the window both before and after data acquisition (combined) (Fig 1). Combined respiratory gating is not used often because more data is discarded, resulting in longer scan times. It is possible, however, that with only retrospective or prospective respiratory gating, the diaphragm may not be within the acceptance window for the entirety of data acquisition (i.e. drifting into or out of the window), negatively affecting image quality. We hypothesized that the combined respiratory gating would result in significantly different estimates of left ventricular strains compared to either retrospective or prospective respiratory gating.

ECG and navigator-free 4D whole-heart coronary MRA

Background Cardiac and respiratory motion artifacts are major challenges to whole-heart coronary MRA. The conventional motion suppression strategies often involve prospective gating based on motion surrogates, e.g. ECG and navigator, which complicates scan setup and prolongs scan time significantly. To address these limitations, an ECG and navigator-free 4D whole-heart coronary MRA technique was recently proposed, providing both cardiac function and coronary artery assessment from a single measurement [1]. In this work, we evaluate the 4D technique by comparing it against conventional cine and coronary MRA protocols.

Delayed contrast enhancement imaging of a murine model for ischemia reperfusion with carbon nanotube micro-CT.

We aim to demonstrate the application of free-breathing prospectively gated carbon nanotube (CNT) micro-CT by evaluating a myocardial infarction model with a delayed contrast enhancement technique. Evaluation of murine cardiac models using micro-CT imaging has historically been limited by extreme imaging requirements. Newly-developed CNT-based x-ray sources offer precise temporal resolution, allowing elimination of physiological motion through prospective gating. Using free-breathing, cardiac-gated CNT micro-CT, a myocardial infarction model can be studied non-invasively and with high resolution. Myocardial infarction was induced in eight male C57BL/6 mice aged 8–12 weeks. The ischemia reperfusion model was achieved by surgically occluding the LAD artery for 30 minutes followed by 24 hours of reperfusion. Tail vein catheters were placed for contrast administration. Iohexol 300mgI/mL was administered followed by images obtained in diastole. Iodinated lipid blood pool contrast agent was then administered, followed with images at systole and diastole. Respiratory and cardiac signals were monitored externally and used to gate the scans of free-breathing subjects. Seven control animals were scanned using the same imaging protocol. After imaging, the heart was harvested, cut into 1mm slices and stained with TTC. Post-processing analysis was performed using ITK-Snap and MATLAB. All animals demonstrated obvious delayed contrast enhancement in the left ventricular wall following the Iohexol injection. The blood pool contrast agent revealed significant changes in cardiac function quantified by 3-D volume ejection fractions. All subjects demonstrated areas of myocardial infarct in the LAD distribution on both TTC staining and micro-CT imaging. The CNT micro-CT system aids straightforward, free-breathing, prospectively-gated 3-D murine cardiac imaging. Delayed contrast enhancement allows identification of infarcted myocardium after a myocardial ischemic event. We demonstrate the ability to consistently identify areas of myocardial infarct in mice and provide functional cardiac information using a delayed contrast enhancement technique.

Image quality and radiation dose of single heartbeat 640-slice coronary CT angiography: A comparison between patients with chronic Atrial Fibrillation and subjects in normal sinus rhythm by propensity analysis

ObjectivesTo evaluate image quality and radiation dose of single heartbeat 640-slice coronary CT angiography (CCTA) in patients with chronic Atrial Fibrillation (cAF) in comparison with subjects in normal sinus rhythm. MethodsA cohort of 71 patients with cAF was matched with 71 subjects in normal sinus rhythm (NSR) and HR≤65bpm using a matched by propensity analysis. All subjects underwent a single heartbeat CCTA with prospective gating. In subjects with cAF, we manually established the acquisition of data only from a single heartbeat. Mean effective dose and image quality, with both objective and subjective measures, were assessed. Results96.4% of all segments in the cAF group had diagnostic image quality. The rate of subjects with at least one non-diagnostic segment was 14% and 2.8% (p=0.031) in the cAF and NRS groups, respectively. In the cAF group, the percentage of patients with at least one non-diagnostic segment for acquisition HR≤72 was 1.8% (1/55), and it did not significantly differ from the NSR group (2.8%; 2/71) (p=1.0). Objective quality parameters did not show a statistically significant difference between the two groups. The mean effective dose was 4.24±1.24mSv in the cAF group and 2.67±0.5mSv in the sinus rhythm group (p<0.0001) with an increase by 59% in the cAF group with respect to the SNR group. ConclusionsA single heartbeat acquisition protocol with a 640-slice prospectively ECG-triggered CT angiography may be feasible in patients with cAF and HR below 72bpm at the CT acquisition, although mean effective dose of this protocol in cAF group was 59% higher than in sinus rhythm one. In patients with cAF and a heart rate higher than 72bpm, CCTA tends to have more movement-associated artefacts.

Combining Coronary with Carotid and Cerebrovascular Angiography Using Prospective ECG Gating and Iterative Reconstruction with 256-slice CT.

To investigate the image quality and radiation dose of combined coronary and carotid/cerebrovascular angiography with ECG gating and iterative reconstruction using 256-slice CT compared with the findings with the two examinations performed separately. One hundred sixty-five consecutive patients underwent a single-injection single-pass combination of coronary and carotid/cerebrovascular CT angiography (group A), coronary CT angiography alone (group B), or carotid/cerebrovascular CT angiography alone (group C). We assessed the image quality of the combined and separate examinations and calculated the respective effective radiation doses. We evaluated the differences in the proportions of image quality grade between the combination and single-examination groups. Diagnostic performance of the combined scanning for detecting significant vascular stenosis has been compared with reference digital subtraction angiography (DSA) in the patient subgroup of group A. There was no significant difference in age, body mass index (BMI), or gender distribution among the 3 groups (all P>0.05). But there was significant difference in scan length, DLP, and effective dose among the 3 groups (all P<0.05). There were no significant differences in the effective radiation dose of coronary scanning between groups A and B (P>0.05), while the effective radiation dose of carotid/cerebrovascular scanning in group A was significantly lower than that in group C (P<0.05), and the total effective radiation dose in group A were relatively low (2.21±1.38mSv). The differences of the proportion of carotid/cerebrovascular image quality grades between groups A and C were not significant (P>0.05). In a subgroup of group A of 30 patients with DSA, combined computed tomographic angiography successfully detected 56 coronary stenosis on per-segment basis, and 62 stenosis on carotid and cerebral artery. The sensitivity, specificity, positive and negative predictive value (NPV) of coronary stenosis were 91.80%, 95.60%, 87.50% and 97.21%, respectively. The sensitivity, specificity, positive and NPV of carotid/cerebrovascular stenosis were 93.55%, 94.68%, 92.06% and 95.70%, respectively. Combination of coronary and carotid/cerebrovascular angiography with 256-slice CT scanner with prospective ECG gating and iterative reconstruction produces diagnostic-quality images of the coronary, carotid, and cerebrovascular systems in a single examination, using less contrast medium and a lower radiation dose than when the two examinations are performed separately. This novel technique has high accuracy in detecting significant stenosis in one image setting.

Routine low-radiation-dose coronary computed tomography angiography

Recent advances in coronary computed tomography angiography (CCTA) increased its utilization as a tool for non-invasive detection of coronary artery disease (CAD). The aim of this analysis is to determine the impact of adopting new radiation dose-reducing techniques on the radiation exposure in consecutive patients undergoing CCTA. We included 1341 consecutive patients who underwent CCTA to rule out CAD between January 2007 and December 2013. New dose-reducing techniques were adopted in July 2010 in 1034 patients. These included high pitch scanning, 100 KVP (Kilovoltage Peak) imaging, and iterative reconstruction. The total radiation dose was calculated for each scan from the dose length product multiplied by conversion factor (0.014). The annual median radiation doses were compared over the study period. After the adoption of the new scanning techniques ( n = 578), 53% of the scans were done with high pitch scanning, 46% with prospective gating, and 1% with retrospective gating. This was associated with >90% reduction in the radiation doses with a median radiation dose of 2.7, 1.5, 1.7, and 1.5 mSv (Millisievert) in 2010, 2011, 2012, and 2013, respectively. A total of 15 and 66% of the CCTA scans had a radiation dose of <1 and 2 mSv, respectively. There was no difference in the frequency of non-diagnostic studies or imaging quality before and after July 2010. Our analysis demonstrates that, in the current era, low-radiation CCTA can be routinely done in clinical practice.

Free-breathing, zero-TE MR lung imaging.

The investigation of three-dimensional radial, zero-echo time (TE) imaging for high-resolution, free-breathing magnetic resonance (MR) lung imaging using prospective and retrospective motion correction. Zero-TE was implemented similarly to the rotating-ultra-fast-imaging-sequence, providing 3D, isotropic, radial imaging with proton density contrast. Respiratory motion was addressed using prospective triggering (PT), prospective gating (PG) and retrospective gating (RG) with physiological signals obtained from a respiratory belt and interleaved pencil beam and DC navigators. The methods were demonstrated on four healthy volunteers at 3T. 3D, radial zero-TE imaging with high imaging bandwidth and nominally zero echo-time enables efficient capture of short-lived signals from the lung parenchyma and the vessels. Compared to Cartesian encoding, unaccounted for free-breathing respiration resulted in only benign blurring artifacts confined to the origin of motion. Breath holding froze respiration but achieved only limited image resolution (~1.8 mm, 30 s). PT and PG obtained similar quality expiratory-phase images at 1.2 mm resolution in ~6 min scan time. RG allowed multi-phase imaging in ~15 min, derived from eight individually stored averages. Zero-TE appears to be an attractive pulse sequence for 3D isotropic lung imaging. Prospective and retrospective approaches provide high-quality, free-breathing MR lung imaging within reasonable scan time.

Oxygen-enhanced 3D radial ultrashort echo time magnetic resonance imaging in the healthy human lung.

The purpose of this work was to use 3D radial ultrashort echo time (UTE) MRI to perform whole-lung oxygen-enhanced (OE) imaging in humans. Eight healthy human subjects underwent two 3D radial UTE MRI acquisitions (TE = 0.08 ms): one while breathing 21% O2 and the other while breathing 100% O2. Scans were each performed over 5 min of free breathing, using prospective respiratory gating. For comparison purposes, conventional echo time (TE = 2.1 ms) images were acquired simultaneously during each acquisition using a radial " outward-inward" k-space trajectory. 3D percent OE maps were generated from these images. 3D OE maps showing lung signal enhancement were generated successfully in seven subjects (technical failure in one subject). Mean percent signal enhancement was 6.6% ± 1.8%, near the value predicted by theory of 6.3%. No significant enhancement was seen using the conventional echo time data, confirming the importance of UTE for this acquisition strategy. 3D radial UTE MRI shows promise as a method for OE MRI that enables whole-lung coverage and isotropic spatial resolution, in comparison to existing 2D OE methods, which rely on a less time-efficient inversion recovery pulse sequence. These qualities may help OE MRI become a viable low-cost method for 3D imaging of lung function in human subjects.

MO‐PIS‐Exhibit Hall‐01: Imaging: CT Dose Optimization Technologies I

MO‐PIS‐Exhibit Hall‐01: Imaging: CT Dose Optimization Technologies I

SU‐E‐QI‐14: Quantitative Variogram Detection of Mild, Unilateral Disease in Elastase‐Treated Rats

Purpose:Determining the presence of mild or early disease in the lungs can be challenging and subjective. We present a rapid and objective method for evaluating lung damage in a rat model of unilateral mild emphysema based on a new approach to heterogeneity assessment. We combined octree decomposition (used in three‐dimensional (3D) computer graphics) with variograms (used in geostatistics to assess spatial relationships) to evaluate 3D computed tomography (CT) lung images for disease.Methods:Male, Sprague‐Dawley rats (232 ± 7 g) were intratracheally dosed with 50 U/kg of elastase dissolved in 200 μL of saline to a single lobe (n=6) or with saline only (n=5). After four weeks, 3D micro‐CT images were acquired at end expiration on mechanically ventilated rats using prospective gating. Images were masked, and lungs were decomposed to homogeneous blocks of 2×2×2, 4×4×4, and 8×8×8 voxels using octree decomposition. The spatial variance – the square of the difference of signal intensity – between all pairs of the 8×8×8 blocks was calculated. Variograms – graphs of distance vs. variance – were made, and data were fit to a power law and the exponent determined. The mean HU values, coefficient of variation (CoV), and the emphysema index (EI) were calculated and compared to the variograms.Results:The variogram analysis showed that significant differences between groups existed (p&lt;0.01), whereas the mean HU (p=0.07), CoV (p=0.24), and EI (p=0.08) did not. Calculation time for the variogram for a typical 1000 block decomposition was ∼6 seconds, and octree decomposition took ∼2 minutes. Decomposing the images prior to variogram calculation resulted in a ∼700x decrease in time as compared to other published approaches.Conclusions:Our results suggest that the approach combining octree decomposition and variogram analysis may be a rapid, non‐subjective, and sensitive imaging‐based biomarker for quantitative characterization of lung disease.

Meta-analysis: diagnostic accuracy of coronary CT angiography with prospective ECG gating based on step-and-shoot, Flash and volume modes for detection of coronary artery disease.

To investigate the diagnostic performance of coronary computed tomographic angiography (CCTA) with prospective electrocardiograph (ECG) gating based on step-and-shoot (SAS), Flash and volume imaging modes. We searched the electronic databases PubMed for all published studies regarding CCTA. We used an exact binomial rendition of the bivariate mixed-effects regression model developed for synthesis of diagnostic data. A total of 21,852 segments, 4,851 vessels and 1,375 patients were identified using database searches. Patient-level pooled sensitivity was 0.99 (95% confidence interval [CI], 0.98-1.00); specificity was 0.88 (CI, 0.85-0.91). The results showed that the sensitivity and specificity for detection of significant stenosis did not differ in the three protocols (P = 0.24). No heterogeneity was found at the patient level for sensitivity (Q = 26.23; P = 0.12; I (2) = 27.56% [CI, 0.00-67.02%]) and specificity (Q = 19.54; P = 0.42; I (2) = 2.78% [CI, 0.00-66.26%]). CCTA with prospective ECG gating has similar high diagnostic value to rule out CAD in all three presented modes. • The accuracy of CCTA with different prospective ECG gating is similar • CCTA with prospective ECG gating is effective to exclude coronary artery disease • The radiation dose of volume mode increases with higher heart rate.

Analysis of myocardial perfusion from vasodilator stress computed tomography: Does improvement in image quality by iterative reconstruction lead to improved diagnostic accuracy?

BackgroundIterative reconstruction (IR) in cardiac CT has been shown to improve confidence of interpretation of noninvasive coronary CT angiography (CTA). ObjectiveWe hypothesized that IR would also improve the quality of vasodilator stress coronary CT images acquired with low tube voltage to assess myocardial perfusion and the accuracy of the detection of perfusion abnormalities by using quantitative 3-dimensional (3D) analysis. MethodsWe studied 39 consecutive patients referred for coronary CTA (256-slice scanner; Philips), who underwent additional imaging (100 kV, prospective gating) with regadenoson (0.4 mg; Astellas). Stress images were reconstructed with different algorithms: filtered back projection (FBP) and IR (iDose; Philips). Image quality was quantified by signal-to-noise and contrast-to-noise ratios in the blood pool and the myocardium. Then, FBP and separately IR images were analyzed with custom 3D analysis software to quantitatively detect perfusion defects. Accuracy of detection was compared with perfusion abnormalities predicted by coronary stenosis >50% on coronary CTA. ResultsFive patients with image artifacts were excluded. In the remaining 34 patients, both signal-to-noise and contrast-to-noise ratios increased with IR, indicating improvement in image quality compared with FBP. For 3D perfusion analysis, 10 patients with normal coronary arteries were used as a reference to correct for x-ray attenuation variations in normal myocardium. In the remaining 24 patients, reduced noise levels in the IR images compared with FBP resulted in tighter attenuation distribution and improved detection of perfusion abnormalities. ConclusionIR significantly improves image quality on regadenoson stress CT images acquired with low tube voltage, leading to improved 3D quantitative evaluation of myocardial perfusion.

Retrospective gating leads to more accurate velocity measurements than prospective gating in spiral phase velocity mapping

Background Spiral phase velocity mapping (PVM) has been used to assess both blood flow [1] and myocardial velocities [2]. Data is usually acquired over several heartbeats which, will not be exactly the same due to physiological RR interval (RR) variations. The way in which the data from different cycles is combined depends on the method of ECG gating. This simulation study investigates the effect of RR variation on the velocities measured for prospective (pro) and retrospective (retro) gating.

Absorbed radiation dose in radiosensitive organs using 64- and 320-row multidetector computed tomography: a comparative study.

Aim. To determine absorbed radiation dose (ARD) in radiosensitive organs during prospective and full phase dose modulation using ECG-gated MDCTA scanner under 64- and 320-row detector modes. Methods. Female phantom was used to measure organ radiation dose. Five DP-3 radiation detectors were used to measure ARD to lungs, breast, and thyroid using the Aquilion ONE scanner in 64- and 320-row modes using both prospective and dose modulation in full phase acquisition. Five measurements were made using three tube voltages: 100, 120, and 135 kVp at 400 mA at heart rate (HR) of 60 and 75 bpm for each protocol. Mean acquisition was recorded in milligrays (mGy). Results. Mean ARD was less for 320-row versus 64-row mode for each imaging protocol. Prospective EKG-gated imaging protocol resulted in a statistically lower ARD using 320-row versus 64-row modes for midbreast (6.728 versus 19.687 mGy, P < 0.001), lung (6.102 versus 21.841 mGy, P < 0.001), and thyroid gland (0.208 versus 0.913 mGy; P < 0.001). Retrospective imaging using 320- versus 64-row modes showed lower ARD for midbreast (10.839 versus 43.169 mGy, P < 0.001), lung (8.848 versus 47.877 mGy, P < 0.001), and thyroid gland (0.057 versus 2.091 mGy; P < 0.001). ARD reduction was observed at lower kVp and heart rate. Conclusions. Dose reduction to radiosensitive organs is achieved using 320-row compared to 64-row modes for both prospective and retrospective gating, whereas 64-row mode is equivalent to the same model 64-row MDCT scanner.

Effect of Tube Voltage (100 vs. 120 kVp) on Radiation Dose and Image Quality using Prospective Gating 320 Row Multi-detector Computed Tomography Angiography

Objectives:The objective of the following study is to evaluate the effect of reducing tube voltage from 120 to 100 kVp using prospective gating 320 row multi-detector computed tomography angiography on image quality and reduction in radiation dose.Materials and Methods:A total of 78 sequential patients were scanned with prospective electrocardiogram gating. A total of 45 patients (Group 1) with mean body mass index (BMI) 29 ± 2 and heart rate (HR) 57 ± 7 beats per minute (BPM) were scanned at 120 kVp. 33 patients (Group 2) with mean BMI 23 ± 3 and HR 58 ± 6 bpm were scanned at 100 kVp. Effective dose was calculated using dose length product and factor (k = 0.014). Quantitative assessment of image quality was calculated by measuring signal to noise ratio (SNR) and contrast to noise ratio (CNR) in the left ventricle and left main coronary artery. Two experienced cardiac radiologists using a three-point ordinal scale assessed subjectively image quality.Results:In Group 1, the median radiation dose was 5.31 mSv (95% confidence interval [CI]: 4.86-6.09) and for Group 2 (P = 0.009) the mean radiation dose was 3.71 mSv (95% CI: 2.76-4.87), representing 30% decrease in radiation dose. In multivariate analyses, adjusting for age, gender, HR, BMI, tube current and scan length, an absolute median reduction of 2.21 mSv (1.13-3.29 mSv) was noted in patients scanned with 100 kVp (P < 0.0001). The quantitative image quality (SNR and CNR) was not statistically significant between the groups. Subjective image quality was rated as good or excellent in 99% of coronary segments for both groups (P value was considered as non-significant).Conclusion:Our study suggests that radiation dose may be lowered from 120 to 100 kVp with preservation of image quality in patient's whose BMI is ≤27.