Types Of CT Scanners Research Articles

3:18 PM Abstract No. 252 Efficacy of cryoablation in treating osteoid osteoma in the pediatric population

Osteoid osteoma (OO) is a benign bone tumor that can cause significant pain and negatively affect daily life for patients. Surgical resection and multiple percutaneous techniques have been utilized in the treatment of osteoid osteomas. We report our institutional experience with cryoablation in the treatment of OO in pediatric patients. A retrospective review of 11 patients from 2014-2017 with a confirmed OO and who underwent cryoablation by a single interventional radiologist was completed. Demographic, subjective, clinical, imaging, and pathological information were collected. Pre- and post-pain scales were recorded to determine if symptom relief was achieved. Bone biopsies were analyzed for concordance with clinical/imaging diagnosis. Details of the procedure, such as imaging modality used, technical success, procedure time, radiation exposure, and complications of each procedure were analyzed. All patients presented with classical symptoms with an average age of 12.1, and 82% were male. The average duration of pain was 11 months and 91% reported regular NSAID use prior to cryoablation. The average nidus size was 9.7 mm. A 100% technical success rate was achieved with 60% of patients having a concordant biopsy. There was a significant reduction in numeric pain scales from an average of 7 out of 10 before to an average of 0 after the procedure (p = 0.003). A total of 3 self-limiting complications were reported after the procedure: one patient reported skin blistering and two presented with temporary nerve injury. There was no significant difference in procedure time, radiation exposure, and technical success between the two types of CT scanners used (p > 0.05). Adequate symptom relief can be achieved with percutaneous cryoablation, which is an effective alternative to other percutaneous techniques or surgical resection in the treatment of osteoid osteoma.

Discriminative feature representation: an effective postprocessing solution to low dose CT imaging**This research was supported by National Natural Science Foundation under grants (81370040, 81530060), the Fundamental Research Funds for the Central Universities, and the Qing Lan Project in Jiangsu Province.

This paper proposes a concise and effective approach termed discriminative feature representation (DFR) for low dose computerized tomography (LDCT) image processing, which is currently a challenging problem in medical imaging field. This DFR method assumes LDCT images as the superposition of desirable high dose CT (HDCT) 3D features and undesirable noise-artifact 3D features (the combined term of noise and artifact features induced by low dose scan protocols), and the decomposed HDCT features are used to provide the processed LDCT images with higher quality. The target HDCT features are solved via the DFR algorithm using a featured dictionary composed by atoms representing HDCT features and noise-artifact features. In this study, the featured dictionary is efficiently built using physical phantom images collected from the same CT scanner as the target clinical LDCT images to process. The proposed DFR method also has good robustness in parameter setting for different CT scanner types. This DFR method can be directly applied to process DICOM formatted LDCT images, and has good applicability to current CT systems. Comparative experiments with abdomen LDCT data validate the good performance of the proposed approach.

Optimization of Dose Parameters to Patients Undergoing CT Scan Using Four Different CT Scanners with International Guidelines

Although the use of CT in medical diagnosis delivers radiation doses to patients that are higher than those from other radiological procedures, lack of proper optimized protocols could be an additional source of increased dose in developing countries. The aims of this study is to determine the variations of doses to patients undergoing CT scan using four different CT scanners with different CT scanning protocols for the purposes of optimizations and to compare with other available international standard and guidelines. The method involve the use of patients scanning protocol and image data to estimate patient body regional doses with four common CT examinations. These were obtained from four CT units/hospitals in Ghana. A large variation of mean body regional doses among different CT scanners were observed for similar CT examinations. These variations largely originated from different CT scanning protocols used, with different CT scanner type. The measured CTDIVOL with GE Lightspeed VCT 64 scanner for head, hest, abdomen and pelvis were 7.7mGy, 12.5 mGy, 14.4 mGy, and 12.9 mGy, respectively. Similarly, Philip 16 scanner recorded 6.6mGy, 13.1mGy, 14.8mGy, and 14.5mGy respectively. Furthermore, Siemen Emotion 16 scanner recorded 5.9mGy, 14.2mGy, 16.8mGy and 12.0mGy respectively. While, Toshiba Aquilion one scanner had CTDIVOL value which varies as 7.2mGy, 13.4mGy, 15.2mGy and 13.5mGy respectively. In conclusion the values were mostly lower than the values of CTDI and DLP as reported in literature for EC, IAEA, ICRP, ACR and AAPM Guidelines.

WE‐FG‐207B‐10: Dual‐Energy CT Monochromatic Image Consistency Across Vendors and Platforms

Purpose:Although dual‐energy CT provides improved sensitivity of HU for certain tissue types at lower simulated energy levels, if these values vary by scanner type they may impact clinical patient management decisions. Each manufacturer has selected a specific dual‐energy CT approach (or in one case, three different approaches); understanding HU variability among low monochromatic images may be required when more than one dual‐energy CT scanner type is available for use.Methods:A large elliptical dualenergy quality control phantom (Gammex Inc.; Middleton, WI) containing several standard tissue type materials was scanned at least three times on each of the following systems: GE HD750, prototype GE Revolution CT with GSI, Siemens Flash, Siemens Edge, Siemens AS 128, and Philips IQon. Images were generated at 50, 70, and 140 keV. Soft tissue and Iodine HU were measured on a single central 5mm‐thick image; NIST constants were used to calculate the ideal HU for each material. Scan acquisitions were approximately dose‐matched (∼25mGy CTDIvol) and image parameters were held as consistent as possible (thickness, kernel, no noise reduction).Results:Measured soft tissue (29 HU at 120 kVp) varied from 28 HU to 44 HU at 50 keV (excluding one outlier), from 21 HU to 31 HU at 70 keV, and from 19 HU to 32 HU at 140 keV. Measured iodine (5mg/ml, 106 HU at 120 kVp) varied from 246 HU to 280 HU at 50 keV, from 123 HU to 129 HU at 70 keV, and from 22 HU to 32 HU at 140 keV.Conclusion:Measured HU in standard rods across 3 dual‐energy CT manufacturers and 6 scanner models varied directly with monochromatic level, with the most variability was observed at 50 keV and least variability at 70keV. Future work will include additional scanner platforms and how measurement variability impacts radiologists.This research has been supported by funds from Dr. William Murphy, Jr., the John S. Dunn, Sr. Distinguished Chair in Diagnostic Imaging at MD Anderson Cancer Center.

The changing use of pediatric CT in Australia.

Despite the medical benefits of CT, there are concerns about increased cancer risks following CT scans in childhood. To assess Australian temporal trends in pediatric CT scans funded through Medicare over the period 1985 to 2005, as well as changes in the types of CT scanners used. We studied de-identified electronic records of Medicare-funded services, including CT scans, that were available for children and adults younger than 20years between 1985 and 2005. We assessed temporal trends using CT imaging rates by age, gender and anatomical region. Regulators provided CT scanner registration lists to identify new models installed in Australia and to date the introduction of new technologies. Between 1985 and 2005, 896,306 Medicare-funded CT services were performed on 688,260 individuals younger than 20years. The imaging rate more than doubled during that time period. There were more than 1,000 CT scanners on registration lists during the study period. There were both a sharp increase in the availability of helical scanning capabilities from 1994 and significant growth in multi-detector CT scanners from 2000. Significant increases in the rate of pediatric CT scanning have occurred in Australia. This rate has stabilized since 2000, possibly a result of better understanding of cancer risks.

Lung hyperaeration assessment by computed tomography: correction of reconstruction-induced bias.

BackgroundComputed tomography (CT) reconstruction parameters, such as slice thickness and convolution kernel, significantly affect the quantification of hyperaerated parenchyma (VHYPER%). The aim of this study was to investigate the mathematical relation between VHYPER% calculated at different reconstruction settings, in mechanically ventilated and spontaneously breathing patients with different lung pathology.MethodsIn this retrospective observational study, CT scans of patients of the intensive care unit and emergency department were collected from two CT scanners and analysed with different kernel-thickness combinations (reconstructions): 1.25 mm soft kernel, 5 mm soft kernel, 5 mm sharp kernel in the first scanner; 2.5 mm slice thickness with a smooth (B41s) and a sharp (B70s) kernel on the second scanner. A quantitative analysis was performed with Maluna® to assess lung aeration compartments as percent of total lung volume. CT variables calculated with different reconstructions were compared in pairs, and their mathematical relationship was analysed by using quadratic and power functions.Results43 subjects were included in the present analysis. Image reconstruction parameters influenced all the quantitative CT-derived variables. The most relevant changes occurred in the hyperaerated and normally aerated volume compartments. The application of a power correction formula led to a significant reduction in the bias between VHYPER% estimations (p < 0.001 in all cases). The bias in VHYPER% assessment did not differ between lung pathology nor ventilation mode groups (p > 0.15 in all cases).ConclusionsHyperaerated percent volume at different reconstruction settings can be described by a fixed mathematical relationship, independent of lung pathology, ventilation mode, and type of CT scanner.

Morphologic and epidemiologic differences between Asian and European population in aneurismatic disease of abdominal aorta

Background: In this study, we analyzed epidemiologic characteristics and morphologic differences between Asian and European population in patients with abdominal aorta aneurysm (AAA). Method: We conducted concomitant study in Japan and Europe , in 31 Asian patients (AP) with AAA and 130 control subjects of the same population, and in 30 European patients with AAA and 126 control subjects (EP). We observed various demographic and anthropologic parameters. Aortography was performed in all patients at the same type of CT-scanners using the same examination protocol and postprocessing. For data analysis, various statistical models were used. Results: There are statistically significant differences in multiple epidemiologic and morphologic findings in AAA patients, as well as in comparison with controls in both groups. This is most distinct in terms of anthropologic characteristics and number of risk-factors, and in terms of morphologic findings, in the length of neck of the aneurysm, transverse diameter of abdominal aorta (AA) and common iliac artery (c.i.a), and volumes of c.i.a. We obtained paradoxical results considering diabetes mellitus, which presented itself as a protective factor for AAA. Conclusion: Demographic-epidemiologic analysis accompanied with morphologic measurements using modern imaging modalities enables obtaining new information on pathology of AAA in different races. There are differences in number of risk-factors, and in terms of morphologic findings, in the length neck, angle of the aneurysm, transverse diameters of abdominal aorta (AA) and in the length of common iliac artery (c.i.a), and volume of c.i.a.

Developing patient-specific dose protocols for a CT scanner and exam using diagnostic reference levels.

The management of image quality and radiation dose during pediatric CT scanning is dependent on how well one manages the radiographic techniques as a function of the type of exam, type of CT scanner, and patient size. The CT scanner's display of expected CT dose index volume (CTDIvol) after the projection scan provides the operator with a powerful tool prior to the patient scan to identify and manage appropriate CT techniques, provided the department has established appropriate diagnostic reference levels (DRLs). This paper provides a step-by-step process that allows the development of DRLs as a function of type of exam, of actual patient size and of the individual radiation output of each CT scanner in a department. Abdomen, pelvis, thorax and head scans are addressed. Patient sizes from newborns to large adults are discussed. The method addresses every CT scanner regardless of vendor, model or vintage. We cover adjustments to techniques to manage the impact of iterative reconstruction and provide a method to handle all available voltages other than 120kV. This level of management of CT techniques is necessary to properly monitor radiation dose and image quality during pediatric CT scans.

Relation of Thoracic Aortic Distensibility to Left Ventricular Area (from the Multi-Ethnic Study of Atherosclerosis [MESA

Decreased arterial compliance is an early manifestation of adverse structural and functional changes within the vessel wall. Its correlation with left ventricular (LV) area on computed tomography, a marker of LV remodeling, has not been well demonstrated. The aim of this study was to test the hypothesis that decreasing aortic compliance and increasing arterial stiffness are independently associated with increased LV area. The study population consisted of 3,540 patients (mean age 61 ± 10 years, 46% men) from the Multi-Ethnic Study of Atherosclerosis (MESA) who underwent aortic distensibility (AD) assessment on magnetic resonance imaging and LV area measurement on computed tomography (adjusted to body surface area). Multivariate logistic regression was performed to assess the association between body surface area-normalized LV area >75th percentile and AD after adjusting for baseline clinical, historical, and imaging covariates. Mean LV area index was 2,153 cm(2), and mean AD was 1.84 × 10(3) mm Hg(-1). Subjects in the lowest AD quartile were older, with higher prevalence rates of hypertension, diabetes, and hypercholesterolemia (p <0.05 for all comparisons). Using multivariate linear regression adjusting for demographics, traditional risk factors, coronary artery calcium, and C-reactive protein, each SD decrease was associated with an 18-cm(2) increase in LV area. In addition, decreasing AD quartiles were independently associated with increasing LV area index, defined as >75th percentile. In conclusion, in this multiethnic cohort, reduced AD was associated with increased LV area. Longitudinal studies are needed to determine if decreased distensibility precedes and directly influences increased LV area.

TH‐C‐134‐01: Computed Tomography 2: Dose Basics and Getting the Most From Your Dose

TH‐C‐134‐01: Computed Tomography 2: Dose Basics and Getting the Most From Your Dose

Coronary computed tomography angiography with prospective electrocardiography triggering: a systematic review of image quality and radiation dose

The purpose of this study was to perform a systematic review of the diagnostic accuracy, image quality and radiation dose of prospective electrocardiography (ECG)-triggered coronary computed tomography angiography (CCTA). We searched databases containing studies of CCTA that used prospective ECG-triggering between 2008 and 2011. The effective dose and image quality reported in each study were analysed and compared between the types of multislice CT scanners. We identified 23 studies through this search, with mean assessable coronary segments and effective dose at 96.8% (95% confidence level [CI] 83%, 100%) and 3.6 mSv (95% CI 2.9, 4.3 mSv), respectively. Both quantitative and qualitative assessments of image quality indicated that image quality was achieved in studies using prospective ECG-triggered CCTA, regardless of the type of CT scanners. The pooled estimates of diagnostic values were more than 90% for patient-, vessel- and segment-based assessments. Prospective ECG-triggered CCTA results in high diagnostic accuracy and image quality, with a significantly low radiation dose.

TU‐A‐217BCD‐02: The Role of Physics in CT Protocol Optimization Over the Range of CT Scanner Types: Recommendations and Misconceptions

The understanding of how scan and reconstructions parameters affect image quality, patient dose, and total scan time is essential to the proper optimization of CT scanner protocols. This understanding is greatly complicated by the differences in user interfaces and in the effects of varying scan and reconstruction parameter with scanners from different manufacturers and even with different scanners from the same manufacturer. Certain scan parameters affect patient dose and image quality (kV, mA, rotation time, effective mAs, pitch, noise index (NI), standard deviation, target effective (TE) mAs), while a subset of these affect the total scan time — which is important for breath hold and contrast considerations. There is a logical method of approaching the modifications of these parameters to achieve the necessary diagnostic image quality at the lowest dose, within total scan time limitations. This method must take into account the model and manufacture of CT scanner, but unfortunately has often not been followed in the development of published CT protocols.Some examples of common confusions and misconceptions involving protocol optimization:The automatic exposure control (AEC) systems from various manufacturers have dramatically different interfaces and perform their functions very differently. Even with the use of AEC, optimal CT scans are not usually obtained with a single protocol for all size patients. In AEC mode the dose can be reduced by raising the NI or lowering the TE mAs. However raising the kV can either raise or lower the dose depending on the AEC system used. Imaging infants to large adults can utilize a range of kV from 80 to 140 kV, with large patients requiring a higher NI and lower TE mAs when using AEC.The effects of pitch and the ways to adjust pitch to optimize image quality and patient dose have appeared to be particularly confusing. Raising the pitch above a value of 1.0 is usually not an optimal way to lower dose due to detrimental effects on image artifacts and slice thickness. Instead, the use of a pitch less than 1.0, with shorter rotation times and lower mA is preferred. Pitch values less than 1.0 do not unnecessarily over‐irradiate the patient since the added radiation is effectively utilized in the image reconstruction in reducing image noise. Raising the pitch above 1.0 should be a final step used to reduce the total scan time when it is clinically too long.Learning Objectives:1. Understand the differences in scans and reconstructions parameters between different scanners and the ways in which these parameters affect image quality, patient dose, and total scan time.2. Understand how AEC is used for different CT scanners included its different effects with varying patient size.3. Understand some of the misconceptions involving CT parameters including the role of AEC and pitch in image quality, patient dose, and total scan time.4. Understand the basic principles of CT protocol optimization and how they are affected by scanner type and patient size.

Estimation of the weighted CTDI∞for multislice CT examinations

The aim of this study was to examine the variations of CT dose index (CTDI) efficiencies, ε(CTDI(100))=CTDI(100)/CTDI(∞), with bowtie filters and CT scanner types. This was an extension of our previous study [Li, Zhang, and Liu, Phys. Med. Biol. 56, 5789-5803 (2011)]. A validated Monte Carlo program was used to calculate ε(CTDI(100)) on a Siemens Somatom Definition scanner. The ε(CTDI(100)) dependencies on tube voltages and beam widths were tested in previous studies. The influences of different bowtie filters and CT scanner types were examined in this work. The authors tested the variations of ε(CTDI(100)) with bowtie filters on the Siemens Definition scanner. The authors also analyzed the published CTDI measurements of four independent studies on five scanners of four models from three manufacturers. On the Siemens Definition scanner, the difference in ε(CTDI(W)) between using the head and body bowtie filters was 2.5% (maximum) in the CT scans of the 32-cm phantom, and 1.7% (maximum) in the CT scans of the 16-cm phantom. Compared with CTDI(W), the weighted CTDI(∞) increased by 30.5% (on average) in the 32-cm phantom, and by 20.0% (on average) in the 16-cm phantom. These results were approximately the same for 80-140 kV and 1-40 mm beam widths (4.2% maximum deviation). The differences in ε(CTDI(100)) between the simulations and the direct measurements of four previous studies were 1.3%-5.0% at the center∕periphery of the 16-cm∕32-cm phantom (on average). Compared with CTDI(vol), the equilibrium dose for large scan lengths is 30.5% higher in the 32-cm phantom, and is 20.0% higher in the 16-cm phantom. The relative increases are practically independent of tube voltages (80-140 kV), beam widths (up to 4 cm), and the CT scanners covered in this study.

Evaluation of portable CT scanners for otologic image-guided surgery

Portable CT scanners are beneficial for diagnosis in the intensive care unit, emergency room, and operating room. Portable fixed-base versus translating-base CT systems were evaluated for otologic image-guided surgical (IGS) applications based on geometric accuracy and utility for percutaneous cochlear implantation. Five cadaveric skulls were fitted with fiducial markers and scanned using both a translating-base, 8-slice CT scanner (CereTom(®)) and a fixed-base, flat-panel, volume CT (fpVCT) scanner (Xoran xCAT(®)). Images were analyzed for: (a) subjective quality (i.e., noise), (b) consistency of attenuation measurements (Hounsfield units) across similar tissue, and (c) geometric accuracy of fiducial marker positions. The utility of these scanners in clinical IGS cases was tested. Five cadaveric specimens were scanned using each of the scanners. The translating-base, 8-slice CT scanner had spatially consistent Hounsfield units, and the image quality was subjectively good. However, because of movement variations during scanning, the geometric accuracy of fiducial marker positions was low. The fixed-base, fpVCT system had high spatial resolution, but the images were noisy and had spatially inconsistent attenuation measurements, while the geometric representation of the fiducial markers was highly accurate. Two types of portable CT scanners were evaluated for otologic IGS. The translating-base, 8-slice CT scanner provided better image quality than a fixed-base, fpVCT scanner. However, the inherent error in three-dimensional spatial relationships by the translating-based system makes it suboptimal for otologic IGS use.

Evaluation of organ doses in CT examinations with an infant anthropomorphic phantom

The aim of this study is to evaluate organ doses in infant CT examinations with multi-detector row CT scanners. Radiation doses were measured with radiophotoluminescence glass dosemeters set in various organ positions within a 1-y-old child anthropomorphic phantom and organ doses were evaluated from the measurement values. Doses for tissues or organs within the scan range were 28-36 mGy in an infant head CT, 3-11 mGy in a chest CT, 5-11 mGy in an abdominal-pelvic CT and 2-14 mGy in a cardiac CT. The doses varied by the differences in the types of CT scanners and scan parameters used at each medical facility. Compared with those for children of various ages, the doses in an infant CT protocol were found to be similar to or slightly smaller than those in a paediatric CT for 5- or 6-y-old children.

ESTIMATION OF THE NUMBER OF CT PROCEDURES BASED ON A NATIONWIDE SURVEY IN JAPAN

In 2007, a nationwide survey was conducted to determine the frequency of CT procedures in Japan in order to compare the current use of CT among developed countries. The frequency of adult and pediatric CT scans was estimated using a model based on the results of the survey. Survey questionnaires were sent to 2,266 CT facilities: 1,068 government hospitals and 1,198 other hospitals and non-hospital medical centers. The questionnaire requested information including the number of beds, outpatients per day, type of CT scanner, various body regions scanned, and the number of scans performed. The results of the study indicate that the number of CT procedures was closely correlated with the number of hospital beds. The authors estimate that approximately 20.5 million procedures were performed in 2005 and 21.2 million in 2006. The number of pediatric CT procedures was calculated by multiplying the total number of CT procedures by the estimated fraction of pediatric (0-15 y) CT procedures. Annual pediatric CT procedures were estimated to have been approximately 580,000 in 2005 and 600,000 in 2006. The present study indicates that the number of procedures per thousand of population, 166 for total CT and 32-34 for pediatric CT, is lower in Japan than in the U.S.

Variation in Pediatric Head CT Imaging Protocols in Washington State

To examine variation in pediatric trauma head CT imaging protocols in Washington state. A web-based survey was sent to trauma-designated hospitals in Washington state. Respondents were queried about pediatric head trauma volumes, type of CT scanners, and technical information about the CT imaging protocols. Variation in pediatric trauma volumes, CT dose reduction strategies, and effective dose by trauma center levels was examined. Mean head effective dose and organ dose for a female baby were estimated. We achieved a 76% overall response rate. Of the 2,215 children who received head CT scans, 36.3% (n=805) received head CT imaging at level 4 trauma center facilities, followed by level 1 trauma center (31.4%; n=695), level 3 trauma center (19.7%; n=436), level 2 trauma center (12%; n=267), and Level 5 (0.5%; n=12) facilities. Most responding trauma center facilities (44/47) reported having a pediatric specific imaging head CT protocols. However, compared to levels 1 and 2 trauma centers together, a greater proportion of levels 3, 4 & 5 trauma center facilities collectively lacked dose reduction strategies (0% vs. 25-57%), tended to have higher mAs (169 ± 113 vs. 110 ± 36), and were later adopters of dose reduction strategies on the CT scanners. There was more than a 10-fold variation in estimated median effective dose for a baby within level 4 trauma center facilities (3.5 ± 0.84 mSv, range 0.60 to 9.60 mSv). There is both within and between trauma center level variation in pediatric head CT imaging protocols and radiation dose in Washington state.

Light scattering in optical CT scanning of Presage dosimeters

The intensity of the scattered light from the Presage dosimeters was measured using a Thorlabs PM100D optical power meter (Thorlabs Inc, Newton, NJ) with an optical sensor of 1 mm diameter sensitive area. Five Presage dosimeters were made as cylinders of 15.2 cm, 10 cm, 4 cm diameters and irradiated with 6 MV photons using a Varian Clinac 2100EX. Each dosimeter was put into the scanning tank of an OCTOPUS" optical CT scanner (MGS Research Inc, Madison, CT) filled with a refractive index matching liquid. A laser diode was positioned at one side of the water tank to generate a stationary laser beam of 0.8 mm width. On the other side of the tank, an in-house manufactured positioning system was used to move the optical sensor in the direction perpendicular to the outgoing laser beam from the dosimeters at an increment of 1 mm. The amount of scattered photons was found to be more than 1% of the primary light signal within 2 mm from the laser beam but decreases sharply with increasing off-axis distance. The intensity of the scattered light increases with increasing light attenuations and/or absorptions in the dosimeters. The scattered light at the same off-axis distance was weaker for dosimeters of larger diameters and for larger detector-to-dosimeter distances. Methods for minimizing the effect of the light scattering in different types of optical CT scanners are discussed.

Evaluation of skin exposure during cerebral CT perfusion studies on a phantom

To evaluate the skin dose during cerebral CT perfusion on a phantom, and estimate the weighted CT dose index (CTDIw) to maximum skin dose conversion factors for four types of CT scanners. We evaluated the relationship between surface dose during cerebral CT perfusion and distance from the scan center in the x-y plane using a 64-multidetector row CT scanner. Skin doses were also assessed with 4 different 64-multidetector CT scanners. The surface doses decreased with the distance from the scan center in the x-y plane. The surface doses at the points 6 cm and 10 cm from the scan center in the x-y plane were different from the dose at the point 8 cm by about 15%. CTDIw and skin doses differed among the CT scanners (CTDIw, 143-590 mGy; averaged temporal skin dose, 126-590 mGy). For all the four types of CT scanner, the doses increased in the following order: occipital point<frontal point<temporal points. The ratios of the maximum skin dose (averaged temporal skin dose) to CTDIw differed among the CT scanners (64-100%). The maximum skin dose during cerebral CT perfusion and the dose to CTDIw ratios differs among CT scanners. The CTDIw is useful for estimation of the maximum skin dose during cerebral CT perfusion using a proper conversion factor specific to each type of CT scanner.

SU-GG-I-07: Monitoring Radiation Dose in Cerebral CT Perfusion Exams

PURPOSE: This paper is to study how to monitor and manage the radiation dose in cerebral CT perfusion exams with various CT scanners including a 10 slice MDCT, a 64 slice VCT and a 320 detector row volume scanner. METHODS & MATERIALS: Several cerebral CT perfusion protocols have been studied with various tube current settings. Radiation dose measurements were done on an anthropormorphic head phantom using an optically stimulated luminescence (OSL) dosimeter device (MicroStar, Landauer) and an ion chamber dosimeter (Accu-Pro, RadCal). All the measurements were done at the skin surface. Several OSLs were used to cover the X-ray slice beam width. The readout of OSLs was performed right on site with a portable reading device. RESULTS: The accuracy of the OSLs was verified through a side-by-side comparison with an ion chamber dosimeter. It is shown that the OSL sensor is angle independent that makes it advantageous over those solid state personal dosimeters for real-time CT dose measurements. For our study, 80 kVp was utilized for the cerebral CT perfusion exams. The tube current varied from 80 mA to 200 mA. The radiation dose varied directly with the selection of tube voltage and current settings. Considerable variations were also observed among different types of CT scanners. Conclusion: Since there is a potential risk for the skin dose to be accumulated beyond the threshold for determinant effects such as skin erythema and epilation in CT perfusion exams, it is important to optimize the protocol and monitor the patient dose closely. This paper verifies a tool to do that. It can be utilized during the initial set-up of the protocol. Also, it will be useful for individual patient dose monitoring from case to case. It adds the safeguard to high dose CT scans such as cerebral CT perfusion exams.