Computed Tomography Scanning Parameters Research Articles

Reducing radiation exposure from computed tomography of the brain in children — report of a practical approach

To reduce radiation exposure to paediatric neurosurgical patients from computed tomography (CT), a CT scanning protocol - lower radiation dose and selective scan segment (LDSS) protocol was used for CT brain at the authors' hospital. To evaluate the amount of reduction in radiation exposure by using this LDSS protocol compared to their usual protocol, the authors prospectively documented their findings. From May 2010 to June 2011, paediatric neurosurgical patients requiring CT brain, and when it was not a clinical emergency and there was baseline CT or MRI brain available, were evaluated for the LDSS protocol. The LDSS protocol used a lower tube current-time product and a shorter scan length to attain a lower total radiation dose. The CT scanning parameters of the patients' usual CT brain and LDSS CT were recorded and compared. Adverse events were also recorded. A total of 24 paediatric patients were included. Using the LDSS protocol, the effective doses were between 9% and 80% of the usual protocol and, in 20 patients, ≤50% of the usual protocol. The tube voltage was 120 kV. For patients below 10 years old, 100 mA s was adequate for the purposes of their CTs; in some patient categories, it was lower than 100 mA s. For patients aged 10 or above, 150 mA s was used. The scan length varied. Radiation exposure from CT brain in paediatric neurosurgical patients could be reduced by adopting a CT scanning protocol, which aimed dynamically at a lower tube current-time product and a shorter scan length than the usual settings at a hospital.

Patient-size-dependent radiation dose optimisation technique for abdominal CT examinations

Since patient doses from computed tomography (CT) are relatively high, risk-benefit analysis requires dose to patients and image quality be optimised. The aim of this study was to develop a patient-dependent optimisation technique that uses patient diameter to select a combination of CT scanning parameters that minimise dose delivered to patients undergoing abdominal CT examinations. The study was performed using cylindrical phantoms of diameters ranging from 16 to 40 cm in order to establish the relationship between image degradation, CT scanning techniques, patient dose and patient size from two CT scanners. These relationships were established by scanning the phantoms using standard scanning technique followed by selected combinations of scanning parameters. The image noises through phantom images were determined using region of interest software available in both scanners. The energy depositions to the X-ray detector through phantoms were determined from measurements of CT dose index in air corrected for attenuation of the phantom materials. The results demonstrate that exposure settings (milliampere seconds) could be reduced by up to 82 % for smaller phantom relative to standard milliampere seconds, while detector signal could be reduced by up to 93 % for smaller phantom relative to energy depositions required when scanned using standard scanning protocols. It was further revealed that the use of the object-specific scanning parameters on studies performed with phantom of different diameters could reduce the incident radiation to small size object by up to 86 % to obtain the same image quality required for standard adult object. In view of the earlier mentioned fact, substantial dose saving from small-sized adults and children patients undergoing abdomen CT examinations could be achieved through optimal adjustment of CT scanning technique based on the patient transverse diameter.

Optimisation des paramètres d’acquisition scanographique pour la radiothérapie des tumeurs mobiles

Aim of the study In the case of lung tumor treatment, to adjust 3D helical computed tomography (CT) acquisition parameters using a dynamic phantom and compare to the theory the volumes of a moving object. Materials and methods Three helical CT acquisitions were compared using a Big Bore CT scan : an “initial” 3D CT scan (constructor parameters), an “optimized” 3D CT scan which parameters are chosen to obtain an axial slow scan like acquisition and a 4D CT scan. We used a phantom composed by a ball filled with water set on a dynamic platform moving in the antero-posterior or cranio-caudal direction with a 14 mm amplitude and a 4 s period. For each acquisition and modality (static and dynamic), we quantified the ball volume by automatic contouring and we estimated relative errors. Results For an antero-posterior displacement, the volume of the moving ball is under estimated by 14.1 % with the “initial” scan, by 0.2 % with the “optimized” scan and over estimated by 0.8 % with the averaged 4D scan. For a cranio-caudal displacement, it is under estimated by about 22 % with the “initial” scan and by about 1 % with the “optimized” scan and the averaged 4D scan. Conclusion Volume measurements performed with the dynamic phantom allowed us to validate the “optimized” 3D CT scan parameters because it accurately reflects the volume of a moving object. Radiotherapy departments without 4D CT should adapt scan parameters for internal target volume definition.

Promotion of Residents' Diagnostic Accuracy of Early Ischemic Infarct on Nonenhanced Brain Computed Tomography With a Modified Window Setting

To assess the effect of a modified window width and center level setting in promoting residents' interpretation of acute ischemic infarct on nonenhanced brain computed tomography (CT). Nonenhanced brain CT images of 11 acute ischemic infarct patients were mixed with 11 control patients. Twelve residents reviewed the randomized images on standard setting (window width and center level of 80 and 30) and then on a modified setting (window width and center level of 40 and 40). There was significant elevation of sensitivity, positive predictive rate, and negative predictive rate (P < 0.05, Paired-Samples test) but no significant difference in specificity. The radiology department of hospitals with picture archiving and communication system may suggest that a modified brain CT setting according to individual CT scanner and scanning parameters accompany the standard settings to assist residents in the detection of acute ischemic infarct. It is a simple, economic, and effective method, which is worthy of more attention.

Effect of Reduced Radiation CT Protocols on the Detection of Renal Calculi

To determine the effect of reduced radiation (tube charge, measured as milliamperes per second) protocols on the sensitivity and specificity of multidetector computed tomography (CT) in the detection of renal calculi. This Health Insurance Portability and Accountability Act-compliant human cadaveric study was approved by the Department of Anatomic Pathology with strict adherence to the university policy for handling donor specimens. Three to five renal stones (range, 2.0-4.0 mm) were randomly placed in 14 human cadaveric kidneys and scanned with a 16-detector CT scanner at 100, 60, and 30 mAs while maintaining other imaging parameters as constant. Following acquisition, images were reviewed independently by two radiologists who were blinded to the location and presence of renal calculi. Interobserver agreement was measured with kappa statistics. The McNemar test was used to compare the sensitivity and specificity between different radiation settings for each reader. Specificity for both readers ranged from 105 (0.95; 95% confidence interval [CI]: 0.90, 0.99) to 109 (0.99; 95% CI: 0.95, 1.0) of 110 without significant differences between 30 and 60 mAs to the standard 100 mAs (P = .500 to >.999). Sensitivity ranged from 42 (0.74; 95% CI: 0.60, 0.84) to 48 (0.84; 95% CI: 0.72, 0.93) of 57, also without significant differences (P = .070 to >.999). When renal calculi detection rates were analyzed by size, 3.0-4.0-mm stones were detected well at all tube charge settings, ranging from 86%-90% (n = 21 for 3.0-mm stones) to 95%-100% (n = 19 for 4.0-mm stones). However, 2.0-mm stones were poorly detected at all tube charge settings (29%-59%; 5-10 of 17). Overall interobserver agreement for stone detection was excellent, with kappa = 0.862. Decreasing the tube charge from 100 to 30 mAs resulted in similar detection of renal stones while reducing patient radiation exposure by as much as 70%. Multidetector CT scanning parameters should be tailored to minimize radiation exposure to the patients while helping detect clinically significant renal stones.

A new high‐resolution computed tomography (CT) segmentation method for trabecular bone architectural analysis

In the last decade, high-resolution computed tomography (CT) and microcomputed tomography (micro-CT) have been increasingly used in anthropological studies and as a complement to traditional histological techniques. This is due in large part to the ability of CT techniques to nondestructively extract three-dimensional representations of bone structures. Despite prior studies employing CT techniques, no completely reliable method of bone segmentation has been established. Accurate preprocessing of digital data is crucial for measurement accuracy, especially when subtle structures such as trabecular bone are investigated. The research presented here is a new, reproducible, accurate, and fully automated computerized segmentation method for high-resolution CT datasets of fossil and recent cancellous bone: the Ray Casting Algorithm (RCA). We compare this technique with commonly used methods of image thresholding (i.e., the half-maximum height protocol and the automatic, adaptive iterative thresholding procedure). While the quality of the input images is crucial for conventional image segmentation, the RCA method is robust regarding the signal to noise ratio, beam hardening, ring artifacts, and blurriness. Tests with data of extant and fossil material demonstrate the superior quality of RCA compared with conventional thresholding procedures, and emphasize the need for careful consideration of optimal CT scanning parameters.

Innovation in Chest Radiology

The guest editors of this issue have been very impressed by the great variety and excellent quality of lung imaging research manuscripts submitted for this issue. We were forced to maintain a very high standard within our review process and are sorry to have disappointed many of you, but in spite of this, we still present you with an overloaded special issue with 17 papers devoted to “Innovation in Chest Radiology.” The breadth of the work becomes obvious if one tries to classify the various papers, as we tried (and failed) to do. It demonstrates how the field of chest imaging is increasingly relying on computer applications, quantification, and early identification of disease, while the focus is changing from purely morphologic description to the incorporation of functional assessment using both magnetic resonance imaging (MRI) and computed tomography (CT). Chest radiography has received renewed interest in the ability to detect nodules, particularly with the use of novel computer assisted diagnosis systems. The study by Bley et al is one in a series of studies that demonstrate the potential impact of computer-aided design systems, 1–3 and further studies are eagerly awaited. The excellent spatial resolution and the natural contrast in the lung allowed CT to remain the mainstay in diagnosing chest disease. Detection of lung nodules is an important issue, albeit that even CT, considered by most the reference standard, has its issues, such as interobserver variability when considering size characteristics as well as measurement methods, 4–6 not to mention the costs and additional investigations associated with CT screening for lung cancer. 7 Nevertheless, it seems that growth over time using computeraided volumetry can provide reproducible and accurate measurement of nodule growth. 8,9 In addition, dynamic contrast-enhanced imaging and CT perfusion imaging using a first pass model was demonstrated as potentially useful for the differentiation between benign and malignant nodules. 10 In addition, these dynamic techniques may help outline malignant and recurrent disease, particularly in a post-treatment situation. 11 CT is regarded as a reference imaging modality in the diagnosis of pulmonary vascular diseases in particular acute pulmonary embolism. Optimization of CT scanning parameters and contrast injection protocols are important for this purpose. 12,13 In the assessment and distinction of pulmonary embolism from other causes of altered pulmonary vascularity, the minimum intensity projection technique 14 and 3D selective-scale texture analysis of CT pulmonary angiography 15 were demonstrated to be useful. Recent studies also show that computer-assisted detection of filling defects within the pulmonary arterial tree may also be a method that could aid the radiologist in the detection of pulmonary embolism. 16,17 CT is steadily gaining ground in the objective quantification of pulmonary emphysema. Currently, lung densitometry for the assessment of pulmonary emphysema has been validated against pathology, pulmonary function, and health status and is a highly reproducible measurement. 18,19 A large multicenter study demonstrated that quantitated

Patient dose reduction methods in computerized tomography procedures: A review

Health hazards are associated with medical exposures to ionizing radiation, including during Computed Tomography (CT) procedures. Rapidly increasing number of CT facilities worldwide is accompanied by enhanced staff, patient and public radiation doses and these needs to be controlled to minimize health risks. This paper reviews the relevant patient and CT scanning parameters that influence patient dose during the common diagnostic procedures. These include scanning geometry, tube current, applied high potential (kVp), scanning mode and length, collimation, couch speed and pitch, gantry rotation speed and radiation shielding. The paper also presents some strategies for limiting patient dose through modulation of exposure parameters and design of technical devices for image processing. These include collimation, filtration, automated modulation of tube current, use of adaptive reconstruction and noise filters. Patient weight and size of the scanned anatomical part influence the absorbed dose, x-ray beam collimation and filtration can reduce dose by 17% to 50%, tube current modulation can lead to 10% to 60% reduction, projection adaptive reconstruction filter can reduce dose by 30% to 60% while noise filters can produce 17% reduction in noise variance compared with the conventional filters. Key phrases: Computerized Tomography, Patient Dose Reduction; Scanning Parameters Modulation.

Effects of Growth Hormone on Visceral Adipose Tissue and Dyslipidemia in HIV, an Erratum

Effects of Growth Hormone on Visceral Adipose Tissue and Dyslipidemia in HIV, an Erratum

Abdominal computed tomography scans in the selection of patients with malignant peritoneal mesothelioma for comprehensive treatment with cytoreductive surgery and perioperative intraperitoneal chemotherapy

Malignant peritoneal mesothelioma is a rare and fatal disease. Until recently, the treatment options were very limited and ineffective. The new comprehensive approach of cytoreductive surgery with perioperative intraperitoneal chemotherapy offers improved survival rates at a cost of considerable morbidity and mortality as in other peritoneal surface malignancies. The outcome after these treatments is predominantly dependent on adequate cytoreduction. The aim of the current study was to identify computed tomography (CT) scan images that are useful in patient selection for this comprehensive approach. An analysis of the preoperative CT scans of 30 patients with peritoneal mesothelioma treated with cytoreductive surgery and perioperative intraperitoneal chemotherapy at a single institution was performed. Based on the size of residual tumor nodules after cytoreductive surgery, patients were divided into 2 groups: those with residual lesions<or=2.5 cm (adequate cytoreduction) and those with residual lesions>2.5 cm (suboptimal cytoreduction). The CT scans for each patient were evaluated by a standardized scoring system with the reader blinded to the operative findings. Thirty-nine CT scan parameters were obtained and statistically analyzed to determine their association with the study outcome variables, namely, adequacy of cytoreduction. Seven patients (64%) in the suboptimal cytoreduction group and 2 patients (11%) in the adequate cytoreduction group had a >5-cm tumor mass in the epigastric region (P=0.004). Nine patients (82%) in the suboptimal group and 2 patients (11%) in the adequate cytoreduction group had CT scans that showed loss of normal architecture of the small bowel and its mesentery (P<0.001). In a composite analysis of these 2 radiologic features, none of the patients with a >5-cm tumor mass in the epigastric region and loss of normal architecture of the small bowel and its mesentery had an adequate cytoreduction. Patients who lacked these two preoperative CT scan findings had a 94% probability of an adequate cytoreduction. CT scans effectively identified large peritoneal mesothelioma tumors at crucial anatomic sites. Because adequate cytoreduction is necessary to achieve prolonged survival, CT scans became an accurate prognostic radiologic test for patient selection for comprehensive treatment.

Single versus Multi–Detector Row CT: Comparison of Radiation Doses and Dose Profiles

Rationale and Objectives The purpose of this study was twofold: ( a) to compare the radiation dose profile between computed tomography (CT) with a single detector row (SD) and with a multi–detector row (MD) and ( b) to compare specific organ doses between SD CT and MD CT. Materials and Methods Thermoluminescent dosimeters placed within a 32-cm-diameter cylindrical phantom were used to measure and compare dose profiles from one SD CT scanner and from one MD CT scanner. SD CT scanning parameters were 210 mA, 140 kVp, pitch of 1.0, 5-mm section thickness, and 0.8-second gantry rotation speed. MD CT scanning parameters were 130 mA, 140 kVp, pitch of 0.75, 4 × 5-mm section thickness, 15-mm table feed, and 0.8-second gantry rotation speed. To plot radiation dose profile, doses were measured both in the imaging plane and in the area adjacent to the imaging plane. The resultant data were normalized to achieve constant image noise between MD CT and SD CT. Direct doses to individual organs from primary and scattered radiation were measured with an anthropomorphic phantom containing thermoluminescent dosimeters and with a standard pelvic imaging protocol for both MD CT and SD CT. Results MD CT resulted in a dose profile approximately 27% higher than that from SD CT in the plane of imaging (8.0 vs 6.3 mGy) and 69% higher adjacent to the plane of imaging (6.8 vs 4.0 mGy). The individual doses to the kidneys, uterus, ovaries, and pelvic bone marrow were 92%–180% higher with MD CT than with SD CT. Conclusion With image noise constant between SD CT and MD CT, the radiation dose profile both inside and outside the plane of imaging was higher with MD CT than with SD CT. Organ dose also was higher with MD CT than with SD CT. This difference should be accounted for in the design of MD CT protocols, especially as MD CT technology becomes more widely available for clinical use.