Comparative study with a moving heart phantom of the impact of temporal resolution on image quality with two multidetector electrocardiography-gated computed tomography units

OBJECTIVE: The objective of this study was to compare the temporal resolution-related image quality of electrocardiography-gated images acquired with two multidetector computed tomography (CT) units with a moving heart phantom, at similar fixed heart rates, using half-scan and multisector acquisition modes. METHODS: An adjustable moving heart phantom (Limbsandthings, Horfield, Bristol, UK) was used. Specific heart rates (47, 55, 64, 66, 69, and 73 beats per minute [bpm]) were chosen. On a General Electric CT unit (LightSpeed Plus; General Electric Medical Systems, Milwaukee, WI), retrospective half-scan and multisector mode protocols were performed. On a Siemens CT unit (Somatom Volume Zoom; Siemens, Forchheim, Germany), a retrospective half-scan mode was performed at 47, 55, and 64 bpm, and a two-sector mode was performed at 66, 69, and 73 bpm. Reformatted maximum intensity projection images were qualitatively compared and related to their temporal resolution. RESULTS: Half-scan mode protocols provided similar good results with both CT units up to 55 bpm. The two-sector mode improved image quality compared with the half-scan mode. High temporal resolution with the multisector mode provided the best results. CONCLUSION: For coronary artery imaging, acquisition protocols that provide the highest temporal resolution are mandatory. The multisector mode is one technique that allows high temporal resolution but may be clinically inappropriate at heart rates below 65 bpm or when heart rate variation is observed during scan time.     

Validation of a Monte Carlo tool for patient-specific dose simulations in multi-slice computed tomography

Estimating the dose delivered to the patient in X-ray computed tomography (CT) examinations is not a trivial task. Monte Carlo (MC) methods appear to be the method of choice to assess the 3D dose distribution. The purpose of this work was to extend an existing MC-based tool to account for arbitrary scanners and scan protocols such as multi-slice CT (MSCT) scanners and to validate the tool in homogeneous and heterogeneous phantoms. The tool was validated by measurements on MSCT scanners for different scan protocols under known conditions. Quantitative CT Dose Index (CTDI) measurements were performed in cylindrical CTDI phantoms and in anthropomorphic thorax phantoms of various sizes; dose profiles were measured with thermoluminescent dosimeters (TLD) in the CTDI phantoms and compared with the computed dose profiles. The in-plane dose distributions were simulated and compared with TLD measurements in an Alderson-Rando phantom. The calculated dose values were generally within 10% of measurements for all phantoms and all investigated conditions. Three-dimensional dose distributions can be accurately calculated with the MC tool for arbitrary scanners and protocols including tube current modulation schemes. The use of the tool has meanwhile also been extended to further scanners and to flat-detector CT.     

降低儿童16层螺旋CT检查辐射剂量的研究

目的论证CT扫描参数kVp和mAs与剂量和图像噪声的关系,在不影响临床诊断的基础上,修正并验证一种基于成人扫描参数的安全可行的儿童16层螺旋CT检查的扫描参数。方法利用16层螺旋CT,采用标准CT剂量指数(CTDI)测试仪、100mm笔型电离室,分别测量16cm和32cm直径模体在2mm×5mm准直宽度时不同kVp和mAs的CTDI;采用20cm标准水模,测量单一感兴趣区域(ROI)标准偏差值SD代表噪声水平。以成人扫描参数的不同百分比修正为不同年龄段儿童CT扫描的参数供临床验证。结果随着kVp和mAs的增加,CTDI随之增加,并与mAs呈线性关系;16cm直径模体的表面CTDI要高于32cm模体58%;实际的加权CTDIw值高于CT扫描仪显示的CTDIw;mAs相同时,kVp越高,图像噪声SD值越低,在kVp固定时,随着mAs的增加,图像噪声SD随之减少,当mAs增加到一定程度后,图像噪声趋向平稳。结论在不影响临床诊断的图像噪声水平下,根据年龄和体型特点,儿童16层CT检查mAs可以比成人降低10%～85%。     

16-slice CT: achievable effective doses of common protocols in comparison with recent CT dose surveys

The aim of the study was to investigate achievable dose levels in 16-slice CT by evaluating CT dose indices (CTDI) and effective doses of dose-optimized protocols compared with 4-slice dose surveys. Normalized CTDI free in air and in 16 cm and 32 cm diameter phantoms were measured on four different 16-slice CT scanners in the Netherlands. All collimation and tube potential settings were analysed. Volume CTDI was calculated for adult protocols for brain, chest, pulmonary angiography (CTPA), abdomen and biphasic liver CT. Effective doses were calculated first using volume CTDI with conversion factors and second from CTDIair values using the ImPACT dose calculator. Average results of the 16-slice scanners were correlated to results of dose surveys with predominantly 4-slice scanners. Statistical analysis was done with Student t-tests with a Bonferroni correction; therefore p < 0.017 was significant. The results of CTDIair and weighted CTDI were documented for all scanners. Effective doses averaged over four scanners for brain, chest, CTPA, abdomen and biphasic liver protocols were 1.9+/-0.4, 3.8+/-0.4, 3.0+/-0.2, 7.2+/-0.9 and 10.2+/-1.3 mSv, respectively. Compared with dose surveys achievable effective doses were equal (p = 0.069) to significantly lower (p < 0.017) for chest and abdomen protocols. For 16-slice spiral brain CT there was a trend of equal doses compared with sequential brain CT in the dose surveys. Thus, with dose-optimized protocols 16-slice CT can achieve equal to lower effective doses in examinations of the chest and abdomen compared with 4-slice CT, while doses can remain stable in the brain.     

Multi-detector row CT: radiation dose characteristics

PURPOSE: To determine the dose characteristics of multi-detector row computed tomography (CT) and to provide tabulated dose values and rules of thumb that assist in minimizing the radiation dose at multi-detector row CT. MATERIALS AND METHODS: Weighted CT dose index (CTDI100w) values were obtained from three multi-detector row CT scanners (LightSpeed; GE Medical Systems, Milwaukee, Wis) for both head and body CT modes by using standard CT-dose phantoms. The CTDI100w was determined as a function of x-ray tube voltage (80, 100, 120, 140 kVp), tube current (range, 50-380 mA), tube rotation time (0.5-4.0 seconds), radiation profile width (RPW) (5, 10, 15, 20 mm), and acquisition mode (helical high-quality and high-speed modes and axial one-, two-, and four-section modes). Statistical regression was performed to characterize the relationships between CTDI100w and various technique factors. RESULTS: The CTDI100w (milligray) increased linearly with tube current: in head mode, CTDI100w = (0.391 mGy/mA +/- 0.004) x tube current (milliampere) (r2 = 0.999); in body mode, CTDI100w = (0.162 mGy/mA +/- 0.002) x tube current (milliampere) (r2 = 0.999). The CTDI100w increased linearly with rotation time: in head mode, CTDI100w = (34.7 mGy/sec +/- 0.2) x rotation time (seconds) (r2 = 1.0); in body mode, CTDI100w = (13.957 mGy/sec +/- 0.005) x rotation time (seconds) (r2 = 1.0). The relationship of normalized CTDI100w (milligrays per 100 mAs) with tube voltage followed a power law: in head mode, CTDI100w = (0.00016 mGy/100 mAs. kVp +/- 0.00007) x (tube voltage)(2.5+/-0.1) (r2 = 0.997); in body mode, CTDI100w = (0.000012 mGy/100 mAs. kVp +/- 0.000007) x (tube voltage)(2.8+/-0.1) (r2 = 0.996). In all scanning modes, CTDI100w decreased when RPW increased. CTDI100w was 10% higher in head mode and 13% lower in body mode compared with the value suggested by the manufacturer, which is displayed at the scanner console. When deposited power exceeded 24 kW, CTDI100w increased by 10% as a result of use of the large focal spot. CONCLUSION: The authors provide a set of tables of radiation dose as a function of imaging protocol to facilitate implementation of radiation dose-efficient studies.     

Effective doses in standard protocols for multi-slice CT scanning

The purpose of this study was to assess the radiation exposure of patients in several standard protocols in multi-slice CT (MSCT). Scanning protocols for neck, chest, abdomen, and spine were examined on a Somatom Plus 4 Volume Zoom MSCT (Siemens, Erlangen, Germany) with changing slice collimation (4×1, 4×2.5, and 4×5 mm), and pitch factors (1, 1.5, and 2). Effective doses were calculated from LiF–TLD measurements at several organ sites using an Alderson-Rando phantom and compared with calculations using the weighted CTDI. Effective dose for MSCT of the neck was 2.8 mSv. For different protocols for MSCT of the chest, 7.5–12.9 mSv were found. In abdominal MSCT protocols, effective dose varied between 12.4 and 16.1 mSv. The MSCT of the spine may lead to 12 mSv. An excellent correlation between the effective dose as determined by LiF–TLD and the calculated effective dose using the weighted CTDI could be demonstrated; however, a difference of up to 30% (mean 14.3%) was noted. Standard protocols for MSCT as measured in this study showed effective doses of up to16 mSv. Phantom measurement data show a good correlation to estimations using the weighted CTDI. Electronic Publication     

Strategies for formulating appropriate MDCT techniques when imaging the chest, abdomen, and pelvis in pediatric patients

OBJECTIVE: Our aim was to formulate appropriate MDCT chest and abdominopelvic CT scan protocols for pediatric patients. MATERIALS AND METHODS: Surface radiation dose measurements from a set of anthropomorphic phantoms (nominal 1 year old, 5 year old, and 10 year old) and an adult phantom were compared with standard CT dose index measurements. Image-noise values on axial 5-mm-thick anthropomorphic phantom images were obtained as a measure of image quality. RESULTS: Peripheral CT dose index values obtained with the standard 16-cm acrylic phantom were within approximately 10% of the CT surface dose measurements for the pediatric anthropomorphic phantoms for both chest and abdominopelvic scan protocols. The noise value for the adult phantom image acquired using a typical clinical CT technique was identified, and targeting this level of noise for pediatric CT examinations resulted in a decrease in dose of 60-90%. Initially, 80 kVp was selected for use with very small children; however, beam-hardening artifacts were severe enough to cause us to abandon this option. Current pediatric protocols at M. D. Anderson Cancer Center rely on 100- and 120-kVp settings. The display field-of-view parameter can be used as a surrogate for patient size to develop clinical pediatric CT protocol charts. CONCLUSION: CT dose index measurements obtained using the 16-cm standard acrylic phantom are sufficiently accurate for estimating chest and abdominopelvic CT entrance exposures for pediatric patients of the same approximate size as the anthropomorphic phantoms used in this study. Image-noise measurements can be used to adjust chest and abdominopelvic CT techniques for pediatric populations, resulting in a decrease in measured entrance dose by 60-90%.     

Effect of dose-reduced scan protocols on cardiac coronary image quality with 64-row MDCT: a cardiac phantom study

OBJECTIVE: To evaluate the feasibility of using relative low-dose scan protocols in coronary imaging with 64-row MDCT. MATERIALS AND METHODS: A pulsating cardiac phantom was used to simulate coronary arteries of two sizes (3 and 5mm in diameter) with three stenosis degrees (25, 50 and 75%) at 55bpm heart rate. Cardiac scans were performed on a 64-row MDCT scanner (GE LightSpeed VCT) with rotation time of 350ms and pitch of 0.2 under six different scan protocols: 120kV/650mA, 1137.5mAs (effective) (CTDI(vol) 121.69mGy), 120kV/550mA, 962.5mAs (CTDI(vol) 102.96mGy), 120kV/450mA, 787.5mAs (CTDI(vol) 84.24mGy), 120kV/350mA, 612.5mAs (CTDI(vol) 65.52mGy), 100kV/590mA, 1032.5mAs (CTDI(vol) 65.17mGy) and 140kV/390mA, 682.5mAs (CTDI(vol) 102.22mGy). The simulative coronary arteries were filled with contrast media to reach 300HU in the lumen. Background noise was measured to describe the basic image quality accordingly. CNR, SNR and contour sharpness represented in slope of CT density curve was calculated as well. Measured stenosis area and rates, described by the percentage area of stenosis on the cross-section images were also calculated. RESULTS: The corresponding image noise levels described in standard deviation of background signals varied with radiation dose, CNR and SNR mainly varied with tube current. The contour sharpness, which can reflect actual spatial resolution, is affected mainly by tube voltage. The first five protocols depicted obviously steeper curves than the sixth one (P<0.05). As for 25% stenosis, there was no significant difference among the stenosis rates of the six protocols (P>0.05). As for evaluation on 50 and 75% stenosis, there was no significant difference between the first two protocols, and between the second two protocols as well. However, significant difference presented between these two groups (P>0.05). When comparing the groups with similar radiation dose, protocols with lower tube voltage gain more accuracy in representing stenosis area and rate. CONCLUSION: Dose level and corresponding image quality is relevant to the accuracy of stenosis evaluation on simulated coronary arteries with 64-row MDCT. In this study, we find relative low-dose protocols with acceptable image quality showed a tendency of overestimating stenosis. Furthermore, using a lower tube voltage and higher tube current to gain accurate imaging result is more applicable than other protocols with the same radiation dose level.     

Diffusion imaging with prospective motion correction and reacquisition

A major source of artifacts in diffusion‐weighted imaging is subject motion. Slow bulk subject motion causes misalignment of data when more than one average or diffusion gradient direction is acquired. Fast bulk subject motion can cause signal dropout artifacts in diffusion‐weighted images and results in erroneous derived maps, e.g., fractional anisotropy maps. To address both types of artifacts, a fully automatic method is presented that combines prospective motion correction with a reacquisition scheme. Motion correction is based on the prospective acquisition correction method modified to work with diffusion‐weighted data. The images to reacquire are determined automatically during the acquisition from the imaging data, i.e., no extra reference scan, navigators, or external devices are necessary. The number of reacquired images, i.e., the additional scan duration can be adjusted freely. Diffusion‐weighted prospective acquisition correction corrects slow bulk motion well and reduces misalignment artifacts like image blurring. Mean absolute residual values for translation and rotation were <0.6 mm and 0.5°. Reacquisition of images affected by signal dropout artifacts results in diffusion maps and fiber tracking free of artifacts. The presented method allows the reduction of two types of common motion related artifacts at the cost of slightly increased acquisition time. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Quantification of coronary artery calcium using multidetector CT and a retrospective ECG-gating reconstruction algorithm.

OBJECTIVE: The purpose of our study was to evaluate the quality of and motion artifacts on multidetector CT scans and to compare the results with those of and on electron beam CT scans for the assessment of coronary calcium scores. MATERIALS AND METHODS: First, 20 volunteers were scanned using multidetector CT. We compared the signal-to-noise ratio in the heart, motion artifacts at the heart border, and the highest CT values in the regions of the coronary arteries using single-sector and multisector reconstruction algorithms. Next, 60 patients with coronary calcified deposits underwent both multidetector CT and electron beam CT. We compared coronary calcium scores determined with multidetector CT using the two algorithms (thresholds of 90 and 130 H) with those determined using electron beam CT. RESULTS: The signal-to-noise ratio was higher and motion artifacts were reduced when we used the multisector algorithm. The highest CT value in the region of the coronary arteries exceeded 90 H in one of 55 arteries on the multisector algorithm images and 17 of 55 arteries on single-sector algorithm images (chi-square test, p < 0.01). In coronary calcium scoring, correlation coefficients ranged from 0.920 to 0.992 (Pearson's product moment) and from 0.932 to 0.969 (Spearman's rank correlation coefficient). CONCLUSION: Multidetector CT with a retrospective ECG-gating algorithm (multisector reconstruction) produced cardiac images with fewer motion artifacts and showed a high correlation with coronary calcium scores determined using electron beam CT. Therefore, multidetector CT is a potential tool for coronary calcium scoring.     

Examination of motion artifacts for helical and non-helical scanning modes in head CT

For head computed tomography (CT), non-helical scanning has been recommended even in the widely used multi-slice CT (MSCT). Also, an acute stroke imaging standardization group has recommended the non-helical mode in Japan. However, no detailed comparison has been reported for current MSCT with more than 16 slices. In this study, we compared the non-helical and helical modes for head CT, focusing on temporal resolution and motion artifacts. The temporal resolution was evaluated by using temporal sensitivity profiles (TSPs) measured using a temporal impulse method. In both modes, the TSPs and temporal modulation transfer factors (MTFs) were measured for various pitch factors using 64-slice CT (Aquilion 64, Toshiba). Two motion phantoms were scanned to evaluate motion artifacts, and then quantitative analyses for motion artifacts and helical artifacts were performed by measuring multiple regions of interest (ROIs) in the phantom images. In addition, the rates of artifact occurrence for retrospective clinical cases were compared. The temporal resolution increased as the pitch factor was increased. Remarkable streak artifacts appeared in the non-helical images of the motion phantom, in spite of the equivalent effective temporal resolution. In clinical analysis, results consistent with the phantom studies were shown. These results indicated that the low pitch helical mode would be effective for emergency head CT with patient movement.     

Dosimetry and adequacy of CT-based attenuation correction for pediatric PET: phantom study

PURPOSE: To evaluate the dose from the computed tomographic (CT) portion of positron emission tomography (PET)/CT to determine minimum CT acquisition parameters that provide adequate attenuation correction. MATERIALS AND METHODS: Measurements were made with a PET/CT scanner or a PET scanner, five anthropomorphic phantoms (newborn to medium adult), and an ionization chamber. The CT dose was evaluated for acquisition parameters (10, 20, 40, 80, 160 mA; 80, 100, 120, 140 kVp; 0.5 and 0.8 second per rotation; 1.5:1 pitch). Thermoluminescent dosimetry was used to evaluate the germanium 68/gallium 68 rod sources. A phantom study was performed to evaluate CT image noise and the adequacy of PET attenuation correction as a function of CT acquisition parameters and patient size. RESULTS: The volumetric anthropomorphic CT dose index varied by two orders of magnitude for each phantom over the range of acquisition parameters (0.30 and 21.0 mGy for a 10-year-old with 80 kVp, 10 mAs, and 0.8 second and with 140 kVp, 160 mAs, and 0.8 second, respectively). The volumetric anthropomorphic CT dose index for newborn phantoms was twice that for adult phantoms acquired similarly. The rod source dose was 0.03 mGy (3-minute scan). Although CT noise varied substantially among acquisition parameters, its contribution to PET noise was minimal and yielded only a 2% variation in PET noise. In a pediatric phantom, PET images generated by using CT performed with 80 kVp and 5 mAs for attenuation correction were visually indistinguishable from those generated by using CT performed with 140 kVp and 128 mAs. With very-low-dose CT (80 kVp, 5 mAs) for the adult phantom, undercorrection of the PET data resulted. CONCLUSION: For pediatric patients, adequate attenuation correction can be obtained with very-low-dose CT (80 kVp, 5 mAs, 1.5:1 pitch), and such correction leads to a 100-fold dose reduction relative to diagnostic CT. For adults undergoing CT with 5 mAs and 1.5:1 pitch, the tube voltage needs to be increased to 120 kVp to prevent undercorrection.     

Evaluation of image quality and dose in renal colic: comparison of different spiral-CT protocols

The aim of this study was to test different technical spiral-CT parameters to obtain optimal image quality with reduced X-ray dose. Images were acquired with a spiral-CT system Philips Tomoscan AVE1, using 250 mA, 120 kV, and 1-s rotational time. Three protocols were tested: protocol A with 5-mm thickness, pitch 1.6, slice reconstruction every 2.5 mm; protocol B with 3-mm thickness, pitch 1.6, slice reconstruction every 1.5 mm; and protocol C with 3-mm thickness, pitch 2, slice reconstruction every 1.5 mm. Two phantoms were employed to evaluate the image quality. Axial images were acquired, then sagittal and coronal images were reconstructed. Finally, the absorbed X-ray dose for each protocol was measured. Regarding image quality, 5-mm-thick images (protocol A) showed greater spatial resolution and lower noise compared with 3-mm-thick images (protocols B and C) on the axial plane; 3-mm reconstructed sagittal and coronal images (protocols B and C) showed an improved image quality compared with 5-mm reformatted images (protocol A). Concerning X-ray dose, the mean dose was: protocol A 19.6 +/- 0.8 mGy; protocol B 14.4 +/- 0.6 mGy; protocol C 12.5 +/- 1.0 mGy. Our study supports the use of thin slices (3 mm) combined with pitch of 1.6 or 2 in renal colic for X-ray dose reduction to the patient and good image quality.     

Comparison of clinical data sets acquired on different tomographs using 6-18F-L-dopa

Longitudinal positron emission tomography (PET) studies of 6-18F-L-dopa uptake in the striatum are used to assess the progression of Parkinson's disease or the survival of neuronal cells grafted in parkinsonian patients. These studies are performed over several years, and data analysis may suffer from the change from old tomographs to new machines with better sensitivity and spatial resolution. Furthermore, such studies on parkinsonian patients may be accomplished in either 2D or 3D acquisition mode. The aforementioned improvements offer great benefits for the study of neurodegenerative diseases, especially those affecting the striatum. However, direct comparison of data is not straightforward owing to variation in scanner characteristics. In this study, we assessed the feasibility of comparing the 6-18F-L-dopa striatal uptake values (Kc) measured in two groups of healthy subjects using two tomographs of different generations. We re-studied and compared acquisitions performed on 14 healthy subjects using 6-18F-L-dopa. Half of these studies had been performed in 2D acquisition mode using an ECAT 953B. The other half had been performed in 3D acquisition mode using an ECAT EXACT HR+. Different reconstruction protocols were used and the Kc values obtained were statistically compared. The results showed that lowering the transverse spatial resolution of images obtained with the scanner having the better spatial resolution, so that it more closely matched that of the other machine, allowed similar KC values to be obtained in healthy subjects. This study shows that quantitative results of 6-18F-L-dopa scans can be matched between different scanners with different intrinsic resolutions. This can be accomplished using adequate modifications of the reconstruction parameters. Such modifications can be used to help in the longitudinal monitoring of parkinsonian patients using different tomographs.     

Single scan PC‐MRI by alternating the velocity encoding gradient polarity between phase encoding steps

The purpose of this study was to develop a faster approach to phase contrast magnetic resonance imaging. This article proposes a phase contrast imaging scheme called single scan phase contrast in which the polarity of the velocity‐encoding gradient is alternated between phase encoding steps. In single scan phase contrast, ghost images due to moving spins form. The signal intensity of the ghost images is modulated by the sine of the motion‐induce phase shift. Prior to image acquisition, the region of interest containing moving spins is identified, and the field of view is configured so to avoid overlap between the object in the image and the ghost image(s) due to motion in the region of interest. The image values of the region of interest and the ghost image are used to quantify velocity. At best, single scan phase contrast reduces the total acquisition time by a factor of two when compared to phase contrast. In this study, single scan phase contrast is validated against phase contrast in phantom and in vivo. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Initial application of respiratory-gated 201Tl SPECT in pulmonary malignant tumours

AIM: Respiratory-gated thallium-201 chloride (201Tl) single photon emission computed tomography (SPECT) was used in preliminary investigations to reduce the adverse respiratory motion effects observed on standard ungated SPECT images and to obtain reliable fusion images with computed tomography (CT) in patients with malignant lung tumours. METHODS: Fifteen patients with primary lung cancer (n=10) or metastatic lung tumours (n=5) underwent gated SPECT 20 min after intravenous injection of 148 MBq 201Tl, using triple-headed SPECT and laser light respiratory tracking units. Projection data were acquired by a step and shoot mode, with 20 stops over 120 degrees for each detector and a preset time of 30 s for each 6 degrees stop. Gated end-inspiratory and ungated images were obtained from 1/8 data centred at peak inspiration for each regular respiratory cycle and for the full respiratory cycle data, respectively. The degree and size of tumour 201Tl uptake were compared between these images by regions of interest (ROI) analysis. Gated SPECT images were registered with rest inspiratory CT images using an automated three-dimensional (3D) image registration tool. Registration mismatch was assessed by measuring the 3D distance of the centroid of 14 201Tl-avid peripheral tumours. Attenuation correction of gated SPECT images was performed using CT attenuation values of these fusion images. RESULTS: Gated SPECT images improved image clarity and contrast of tumour 201Tl uptakes compared with ungated images, regardless of the decreased count density due to the use of gated images. The lesion-to-normal (L/N) lung count ratios and ROI size in 18 well-circumscribed 201Tl-avid tumours were significantly higher and smaller on gated images (both P<0.0001). Gated images showed positive 201Tl uptakes in two small peripheral tumours, although negative on ungated images, and demarcated 201Tl-avid tumours from adjacent 201Tl-avid lymph node or surrounding focal 201Tl uptakes caused by other pathology, although these were not clearly demarcated on ungated images. On fusion images, gated images yielded a significantly better SPECT-CT matching compared with ungated images (P<0.0001). Fusion images accurately localized 201Tl uptakes of tumour/lymph node and other focal pathological/physiological conditions. Attenuation-corrected gated SPECT images further facilitated the detection of 201Tl uptake in small or deeply located lesions, with significantly increased L/N ratios. CONCLUSION: Gated SPECT images facilitate the detection of tumour 201Tl uptake and provide reliable SPECT-CT fusion images, which contribute to accurate interpretation and attenuation correction of Tl SPECT images.     

Study on motion artifacts in coronary arteries with an anthropomorphic moving heart phantom on an ECG-gated multidetector computed tomography unit

Acquisition time plays a key role in the quality of cardiac multidetector computed tomography (MDCT) and is directly related to the rotation time of the scanner. The purpose of this study is to examine the influence of heart rate and a multisector reconstruction algorithm on the image quality of coronary arteries of an anthropomorphic adjustable moving heart phantom on an ECG-gated MDCT unit. The heart phantom and a coronary artery phantom were used on a MDCT unit with a rotation time of 500 ms. The movement of the heart was determined by analysis of the images taken at different phases. The results indicate that the movement of the coronary arteries on the heart phantom is comparable to that in a clinical setting. The influence of the heart rate on image quality and artifacts was determined by analysis of several heart rates between 40 and 80 bpm where the movement of the heart was synchronized using a retrospective ECG-gated acquisition protocol. The resulting reformatted volume rendering images of the moving heart and the coronary arteries were qualitatively compared as a result of the heart rate. The evaluation was performed on three independent series by two independent radiologists for the image quality of the coronary arteries and the presence of artifacts. The evaluation shows that at heart rates above 50 bpm the influence of motion artifacts in the coronary arteries becomes apparent. In addition the influence of a dedicated multisector reconstruction technique on image quality was determined. The results show that the image quality of the coronary arteries is not only related to the heart rate and that the influence of the multisector reconstruction technique becomes significant above 70 bpm. Therefore, this study proves that from the actual acquisition time per heart cycle one cannot determine an actual acquisition time, but only a mathematical acquisition time.     

National survey of doses from CT in the UK: 2003

A review of patient doses from CT examinations in the UK for 2003 has been conducted on the basis of data received from over a quarter of all UK scanners, of which 37% had multislice capability. Questionnaires were employed to collect scan details both for the standard protocols established at each scanner for 12 common types of CT examination on adults and children, and for samples of individual patients. This information was combined with published scanner-specific CT dose index (CTDI) coefficients to estimate values of the standard dose indices CTDI(w) and CTDI(vol) for each scan sequence. Knowledge of each scan length allowed assessment of the dose-length product (DLP) for each examination, from which effective doses were then estimated. When compared with a previous UK survey for 1991, wide variations were still apparent between CT centres in the doses for standard protocols. The mean UK doses for adult patients were in general lower by up to 50% than those for 1991, although doses were slightly higher for multislice (4+) (MSCT) relative to single slice (SSCT) scanners. Values of CTDI(vol) for MSCT were broadly similar to European survey data for 2001. The third quartile values of these dose distributions have been used to derive UK national reference doses for examinations on adults (separately for SSCT and MSCT) and children as initial tools for promoting patient protection. The survey has established the PREDICT (Patient Radiation Exposure and Dose in CT) database as a sustainable national resource for monitoring dose trends in CT through the ongoing collation of further survey data.     

Accelerating image acquisition in 64-MDCT: the influence of scan parameters on image resolution and quality in a phantom study

Computed tomographic (CT) image resolution and quality were evaluated utilizing varying scan protocols with accelerated image acquisition. A resolution phantom with hole diameters from 0.2 to 1.0 mm was scanned in axial, coronal, and sagittal plane using a 64-slice multidetector CT with varying scan parameters. No relevant differences in image resolution and quality were detected between the fastest scan protocol, with the shortest rotation time and highest pitch, and the slowest protocol. Accelerated CT protocols resulted in diagnostic images with adequate resolution and quality.     

Hi-ART螺旋断层放疗机MV螺旋CT剂量指数的测量

目的 探讨Hi-ART螺旋断层放疗机MV扇形束CT图像获取过程中患者接受的剂量。方法 用PTWTM30009CT电离室分别在T40017头部和T40016躯干模体中,选择扫描层厚2、4及6mm和改变扫描范围等参数,分别测量加权CT剂量指数,计算相应的剂量长度乘积,并与XVIkV锥形束CT、ACQSim模拟定位CT的结果进行比较。结果 Hi-ART螺旋断层治疗机的CT剂量指数与层厚成反比,剂量长度乘积与扫描范围成正比。临床应用条件下Hi-ART的CT剂量指数在头颈部比XVIkV锥形束CT大,但躯干较小。结论 CT剂量指数能反映患者成像过程中接受的剂量,可以作为治疗保证与控制的指标。图像引导过程中应该合理选择层厚,减少扫描范围,最大限度减少患者接受剂量。