Selection Of Scan Parameters Research Articles

Optimization of magnetic resonance imaging of the hand

BACKGROUND: Magnetic resonance imaging is one of the leading imaging modalities of the musculoskeletal system. However, when imaging the hand, major problems in magnetic resonance imaging include the lack of specialized coils and reliable fixation devices for the hand, uncomfortable patient posture, motion artifacts, and small anatomical structures in the wrist. These factors inevitably lead to incorrect interpretation. AIM: To improve the quality of magnetic resonance imaging of the hand by developing an approach to coil selection, scanning protocol, and hand positioning and fixation. MATERIALS AND METHODS: A positioning device was developed to prevent hand movements. Two types of coils were evaluated. Magnetic resonance images were evaluated comparatively, as well as by a musculoskeletal radiologist. RESULTS: А head coil is more appropriate when scanning the entire hand, for example, in rheumatic diseases. A knee coil is more appropriate when studying smaller anatomical structures (including the wrist) owing to a smaller field of view and higher resolution. Based on the obtained data, guidelines for the selection of scanning parameters, sequences, and coils for magnetic resonance imaging of the hand were formulated. To prevent motion artifacts, a special fixation device of the patient’s hand was introduced. CONCLUSION: Certain factors directly affect the qualitative magnetic resonance imaging study of the hand, such as safety protocols, scanning parameters, and hand fixation. The guidelines presented in this study and the use of the developed specialized fixation device may improve the quality of magnetic resonance imaging of the hand.

Multiphase CT angiography perfusion maps for predicting target mismatch and ischemic lesion volumes

The complexity of CT perfusion (CTP) acquisition protocols may limit the availability of target mismatch assessment at resource-limited hospitals. We compared CTP mismatch with a mismatch surrogate generated from a simplified dynamic imaging sequence comprising widely available non-contrast CT (NCCT) and multiphase CT angiography (mCTA). Consecutive patients with anterior circulation acute ischemic stroke who received NCCT, mCTA, and CTP were retrospectively included in this study. An mCTA-perfusion (mCTA-P) dynamic series was formed by co-registering NCCT and mCTA. We simulated an ideal mCTA-P study by down-sampling CTP (dCTP) dynamic images according to mCTA timing. Ischemic core and penumbra volumes were estimated by cerebral blood flow and Tmax thresholding, respectively, on perfusion maps calculated independently for CTP, dCTP, and mCTA-P by deconvolution. Concordance in target mismatch (core < 70 ml, penumbra ≥ 15 ml, mismatch ratio ≥ 1.8) determination by dCTP and mCTA-P versus CTP was assessed. Of sixty-one included patients, forty-six had a CTP target mismatch. Concordance with CTP profiles was 90% and 82% for dCTP and mCTA-P, respectively. Lower mCTA-P concordance was likely from differences in collimation width between NCCT and mCTA, which worsened perfusion map quality due to a CT number shift at mCTA. Moderate diagnostic agreement between CTP and mCTA-P was found and may improve with optimal mCTA scan parameter selection as simulated by dCTP. mCTA-P may be a pragmatic alternative where CTP is unavailable or the risks of additional radiation dose, contrast injections, and treatment delays outweigh the potential benefit of a separate CTP scan.

Early differentiation of neurodegenerative diseases using the novel QSM technique: what is the biomarker of each disorder?

During neurodegenerative diseases, the brain undergoes morphological and pathological changes; Iron deposits are one of the causes of pathological changes in the brain. The Quantitative susceptibility mapping (QSM) technique, a type of magnetic resonance (MR) image reconstruction, is one of the newest diagnostic methods for iron deposits to detect changes in magnetic susceptibility. Numerous research projects have been conducted in this field. The purpose of writing this review article is to identify the first deep brain nuclei that undergo magnetic susceptibility changes during neurodegenerative diseases such as Alzheimer's or Parkinson's disease. The purpose of this article is to identify the brain nuclei that are prone to iron deposition in any specific disorder. In addition to the mentioned purpose, this paper proposes the optimal scan parameters and appropriate algorithms of each QSM reconstruction step by reviewing the results of different articles. As a result, The QSM technique can identify nuclei exposed to iron deposition in various neurodegenerative diseases. Also, the selection of scan parameters is different based on the sequence and purpose; an example of the parameters is placed in the tables. The BET toolbox in FSL, Laplacian-based phase-unwrapping process, the V_SHARP algorithm, and morphology-enabled dipole inversion (MEDI) method are the most widely used algorithms in various stages of QSM reconstruction.

Dose optimisation in paediatric CT examination: Assessment on current scanning protocols associated with radiation dose

Request for paediatric CT imaging has been increasing recently, and thus assessment of current paediatric CT protocols is of crucial importance as to assess the associated potential risk and possibly identify the need to modify the current practice. The aim of this study was to optimize the current local practice through investigation on the radiation dose distribution and existing routine scanning protocols of paediatric head and abdomen CT examinations at Radiology Department, HUSM, Kelantan, Malaysia. A total of 250 paediatric (age between 0‒12 years) CT examinations (134 of head CT and 116 of abdomen CT scans) were retrospectively collected from PACS and further analysed. The dose metrics in volume CT dose index (CTDIvol) and dose length product (DLP) with combination of exposure parameters (kV, mAs, pitch, scan length and acquisition time) for paediatric CT imaging were evaluated. Third quartile values of local dose distribution were then compared with selected international DRLs. The third quartile values for CTDIvol (mGy) and DLP (mGy.cm) for head and abdomen CT scans with respect to the age groups were 0–3 years (32/557 and 7/232), 4–6 years (61/1105 and 9/251), 7–9 years (117/1454 and 11/405), 10–12years (117/2203 and 14/566) respectively. From the comparative study, the local dose received from paediatric head CT scans were higher than the recommended levels. This is mainly due to selection of scanning parameters which were higher than the optimised paediatric protocols. Tube voltage selection was ranged from 100‒120 kV for all age groups except the head CT scan in group 4 that used a constant 120 kV. Applied mAs varied in the ranges from 100‒410 mAs for head CT scan and 35–100 mAs for abdominal CT scans and increases as the paediatric age increased. From the findings, review and optimisation on the current scanning protocols is required especially for head CT scan to complement the corresponding age groups and sizes while maintaining the diagnostic values.

The incidence of artifacts in cone beam computed tomography images: A pilot study

Aim: Cone-beam computed tomography is an important diagnostic tool in dentistry. However, cone-beam computed tomography technology has various limitations such as image artifacts. The aim of this study was to evaluate the incidence of various artifacts or errors in the cone-beam computed tomography images and to investigate the correlation between artifacts and parameters such as age groups, gender, imaging areas and acquisition times.Material and Methods: Five different types of artifacts were evaluated. Patient’s age, gender, the reason for radiographic examination, the field of view (FOV), acquisition time, anatomical area and presence of artifacts were recorded. The Pearson Chi-Square and Fisher’s Exact test were used for comparisons of the parameters.Results: The images of 600 patients aged from 6 to 88 years (mean age ± standard deviation: 36.2 ±16.8) were examined. The beam hardening (dark band or streaks) were the most common artifacts (38.8%). An increase in the number of artifacts was observed with the increase in FOV and voxel size (p0.05). The prevalence of motion artifacts was 0.7% and a statistically significance was found between motion artifact and age. (p0.05). The cupping and aliasing artifacts were also correlated with the FOV. Conclusion: The results of our study showed that artifacts are an important problem affecting image quality. Careful patient positioning and the optimum selection of scan parameters are the most important factors in preventing image artifact.

Evaluation of some spiral and sequential computed tomography protocols of adults used in three hospitals in Shiraz, Iran with American College of Radiology and European Commission guidelines.

PurposeUse of computed tomography (CT) has increased considerably all over the world. In addition, there has been an increased demand for utilisation of CT scanning in Iran over the past decade, especially after introducing multi-detector computed tomography (MDCT). It should be considered that making a mistake in the selection of scan parameters leads to patients receiving higher doses and having increased risk of cancer. All of these facts prompted us to compare six routine CT protocols in three hospitals in the city of Shiraz, and to compare the results with American College of Radiology (ACR) practice parameters and European Commission (EC) guidelines for dual- and multi-detector CT.Material and methodsIn the studied hospitals, 10 adult patients were chosen randomly for every six protocols, taken by different technologists. Seven and 11 scan factors in sequential and spiral scans, respectively, were compared with ACR (2014) and EC guidelines (EC16262 & EC2004).ResultsThe majority of scan factors in sequential and the spiral protocols that were scrutinised met the guidelines. The CTDIvol and DLPs for sequential and spiral scans were lower than the dose reference level (DRL) pronounced by ACR in three CT departments, and they were compatible with the recommended dose by EC (16262) in a private hospital.ConclusionsBased on accordance of CTDIvol with ACR measurements and incompatibility with EC (2004) in teaching hospitals, we concluded that the recorded doses should be compared with different criteria. A regular review of protocols, using special protocols for different pathologic circumstances and continual education for technologists in the three CT departments, are recommended.

Evaluation of Handheld Scanners for Automotive Applications

The process of generating a computerized geometric model for an existing part is known as Reverse Engineering (RE). It is a very useful technique in product development and plays a significant role in automotive, aerospace, and medical industries. In fact, it has been getting remarkable attention in manufacturing industries owing to its advanced data acquisition technologies. The process of RE is based on two primary steps: data acquisition (also known as scanning) and data processing. To facilitate point data acquisition, a variety of scanning systems is available with different capabilities and limitations. Although the optical control of 3D scanners is fully developed, still several factors can affect the quality of the scanned data. As a result, the proper selection of scanning parameters, such as resolution, laser power, shutter time, etc., becomes very crucial. This kind of investigation can be very helpful and provide its users with guidelines to identify the appropriate factors. Moreover, it is worth noting that no single system is ideal in all applications. Accordingly, this work has compared two portable (handheld) systems based on laser scanning and white light optical scanning for automotive applications. A car door containing a free-form surface has been used to achieve the above-mentioned goal. The design of experiments has been employed to determine the effects of different scanning parameters and optimize them. The capabilities and limitations have been identified by comparing the two scanners in terms of accuracy, scanning time, triangle numbers, ease of use, and portability. Then, the relationships between the system capabilities and the application requirements have been established. The results revealed that the laser scanner performed better than the white light scanner in terms of accuracy, while the white light scanner performed better in terms of acquisition speed and triangle numbers.

Using Age and Weight Specific CT Protocol to Estimate Reference Effective Dose to Patients Undergoing CT Examination

In x-ray computed tomography (CT), the most common parameters used to estimate and minimize patient dose is the CT dose index (CTDI) and DLP. The aim of the study is to serve as a reference values during QC for the purposes of QA in other to reduce doses to patients undergoing CT scan using the age and weight specific CT protocol set out by various manufacturers and other international organizations. This was done by recording CTDI and DLP values to patients within a specific age and weight bracket during scanning on the scanning console and on image data. The effective dose values represents an averaged dose to patients, hence the measurements are only an approximation of the dose to patient, these doses may be overestimated or underestimated by a factor of two or more with CTDI and DLP values in comparison with point dose values. CTDI and DLP were used to evaluate CT scanner output and estimating patient regional effective dose in this study. The estimated head CTDI scans base on the various protocol from all the hospitals increase from approximately 2.8mGy in newborns to approximately 8.7mGy in adults. Resulting with a variation of effective dose from 0.67mSv in new born to approximately 1.03mSv in oversize adults. Neonates head CT effective doses are higher than those for the normal adults except oversize adults as shown in Table 4.4. The chest, abdominal and pelvis CTDI values increases from 2.8, 2.5 and 2.7 mGy in neonates of approximately 3.4kg of weight to 19.84, 7.78 and 11.33mGy in adults of approximately 72.5kg of weight respectively. The estimated effective doses for neonates undergoing chest, abdomen and pelvis of the body CT were 0.83, 6.7, 4.87 and 5.52mSv, whereas those for normal-sized adults are 13.31, 4.61 and 5.34mSv respectively. Chest oversize patients’ examinations exceeded the recommended dose levels of 19.84mSv whiles the head, abdomen and pelvis were: 1.03, 7.16 and 5.98mSv respectively. It was concluded that patient body doses could be substantially minimized through careful selection of scanning parameters based on clinical indications of study, patient age, body size, and body region being examined. Additional dose reduction to superficial body regions would require the use of shielding materials.

On the influence of scanning factors on the laser scanner-based 3D inspection process

3D inspection process is getting more and more interest for manufacturing industries as it helps to carefully check the expected quality of the released products. Much more attention is oriented to optical devices able to quickly capture the whole shape of the product providing many useful information on the process variability and the deliverability of the key characteristics linked to the quality of the product/process. Although the optical control of 3D scanners is mature enough, many factors may influence the quality of the scanned data. These factors may be strictly related to internal elements to the acquisition device, such as scanner resolution and accuracy, and external to it, such as proper selection of scanning parameters, ambient lighting and characteristics of the object surface being scanned (e.g. surface colour, glossiness, roughness, shape), as well as the sensor-to-surface relative position. For the 3D laser-based scanners, the most common on the market, it would be of great industrial interest to study some scanning factors mainly affecting the quality of the 3D surface acquisitions and provide users with guidelines in order to correctly set them so to increase the massive usage of these systems in the product inspection activities. In this context, by using a commercial triangulation 3D laser scanner, the effects of some scanning factors that may affect the measurement process were analysed in the present paper. Working on a sheet metal test part, more complex than the ones commonly used in laboratory and documented in the literature, the scanner-to-object relative orientation and the ambient lighting, as well as an internal scanner parameter, were tested. Through a Design of Experiments (DoE) approach, and setting root mean square error (RMSE) as response function, the outcomes of the tests mainly pointed out that the scanner-to-object relative orientation as well as its position within the field of view of the measurement device are the key factors mostly influencing the accuracy of the measurement process.

Management of auto exposure control during pediatric computed tomography.

Automatic exposure control (AEC) is particularly well-suited for pediatric CT scanning. However the importance of the localizer scan portion of exams that relies on AEC is frequently underestimated. This paper explains in detail several crucial aspects of the localizer and their effect on the subsequent cross-sectional (axial or helical) image acquisition. The paper also covers general suggestions regarding AEC influence on the cross-sectional images. AEC systems on CT scanners are becoming more complex; using them effectively in the setting of pediatric CT requires careful selection of scan parameters.

CT Dose Reduction Strategy: To Modulate Dose or Not in Certain Patients?

CT utilization has increased at a double-digit rate and more moderately at a single-digit rate over the past 10 years. Accompanying this growth is the attention to radiation burden from CT scans, and increased scrutiny of the way CT scans are performed has resulted in a variety of CT dose reduction strategies. These strategies include not only technological advances to reduce dose but also review of CT protocols (including undergoing accreditation), better selection of scan parameters to match patients, and simply paying greater attention to the overall CT studies [ 1 McCollough C.H. Primak A.N. Braun N. et al. Strategies for reducing radiation dose in CT. Radiol Clin North Am. 2009; 47: 27-40 Abstract Full Text Full Text PDF PubMed Scopus (606) Google Scholar ]. The implementation of various CT dose reduction strategies has resulted in a downward trend in CT doses. Among the various dose reduction strategies, dose modulation or, more specifically, tube current modulation, is the primary method that has shown significant strength in reducing CT dose with most CT protocols.

Target‐specific optimization of four‐dimensional cone beam computed tomography

Under-sampling artifacts are a major problem in four-dimensional cone-beam computed tomography (4D-CBCT) and may compromise evaluation of target motion. Several studies have addressed scan parameter selection for minimizing under-sampling artifacts; however, the role of the target characteristics in scan parameter selection has not been investigated. In this work, the authors evaluated 4D-CBCT performance by assessing the accuracy of target motion measurements for various target sizes and motions. The results may serve as patient-specific guidelines for scan parameters selection in 4D-CBCT. The authors acquired 4D-CBCT scans of a moving phantom consisting of six water-filled sphere targets of sizes 10-37 mm, using various scan times ranging from 30 s to 3 min., setting the motion to 3-s and 6-s periods. The authors used automatic image registration to extract the target motion trajectories and evaluated these measurements for various target sizes and motions over various combinations of scan parameters including scan time, detector configuration, number of respiration phases, and reconstruction filters. The most important object parameter to 4D-CBCT performance was the period of motion. Measurements for the 6-s motion were always systematically less accurate than measurements for the 3-s motion for 34 of 36 objects of various sizes and periods of motion. The 6-s motion required a greater scan time than the 3-s motion for equivalent measurement accuracy. The second most influential parameter was the target size. For the 3-s period of motion, objects larger than 13 mm were tracked with sub-millimeter accuracy with a 1-min scan time. For the 6-s period of motion, objects larger than 22-mm were tracked with sub-millimeter accuracy with a 1.5-min scan time. For all sizes and motions, temporal blurring was observed when the number of phases was fewer than 8. Offset detector configuration provided the same performance as centered detector except for small targets (20 mm.) at short scan times (≤1 min). Finally, reconstruction filtering and number of respiratory phases did not affect performance. Scan time should be set according to target size and motion. The authors have provided figures that provide the minimum scan time needed to achieve the particular motion measurement accuracy for a particular size and motion period.

SU-E-J-129: Target-Specific Optimization of Four-Dimensional Cone Beam Computed Tomography.

Undersampling artifacts are a major problem in four-dimensional cone-beam computed tomography (4D-CBCT) and may compromise evaluation of target motion. The role of the target characteristics in scan parameter selection has not been previously investigated. In this work, we evaluated 4D-CBCT performance by assessing the accuracy of target motion measurements for various target sizes and motions. The results may serve as patient-specific guidelines for selection of scan parameters in 4D-CBCT. We acquired 4D-CBCT scans of a moving phantom consisting of six water-filled sphere targets of sizes 10 to 37 mm, with various scan times ranging from 30 sec to 3 min. Two different (3-sec and 6-sec) periods of motions were tested. We used automatic image registration to extract the target motion trajectories and evaluated the accuracy of the measurement for the various target sizes and motions for various combinations of scan parameters. The most important object parameter to 4D-CBCT performance was the period of motion. Measurements for the 6-sec motion were always systematically less accurate than measurements for the 3-sec motion for 34 of 36 target sizes/motions for any given scan time. For any given target size, a 45-sec scan for the 3-sec motion yielded nearly equivalent accuracy to a 3-min scan for a 6-sec motion. The second most important parameter was the target size. A 1-min scan was needed for sub-mm motion measurement accuracy of 28-mm target, whereas a 1.5-min scan was needed for the 22-mm target. For all sizes and motions, temporal blurring was observed when the number of phases was fewer than 8. Scan time should be set according to target size and motion. We have provided figures that provide the minimum scan time needed to achieve the particular motion measurement accuracy for a particular size and period of motion.

SU‐E‐J‐125: CT Dose Survey for Simulations in Radiation Oncology

Purpose: To establish baseline values and ranges for CTDIvol and DLP as a function of treatment site to be used to monitor CT simulation protocols and scan techniques for inadvertent changes and patient specific anomalies. Methods: We have collected CTDIvol (mGy) and DLP (mGy cm) values reported for all CT simulations performed on two large bore GE lightspeed RT scanners and one GE PET/CT scanner located in the Radiation Oncology facilities of the University of California San Diego for the calendar year 2010. Additional acquired data included patient identifier, scan date, scan type, intended treatment site and scanner location. Data was analyzed to calculate averages and standard deviations of CTDIvol and DLP as a function of intended treatment site and scan type. Results: The average CTDIvol for all helical scans was 32.3 with a standard deviation of 16.3 while the average DLP was 1095 with a standard deviation of 570. The average CTDIvol for all CINE scans was 115.6 with a standard deviation of 40.3. while the average DLP was 2064 with a standard deviation of 1625. As a function of treatment site for the helical scans, average values for CTDIvol ranged from 16.7 for TBI to 49.1 for brain while DLP ranged from 755 for breast to 1888 for TBI. For the CINE scans, average values for CTDIvol ranged from 113 for lung to 155 for liver while DLP ranged from 1630 for lung to 3929 for liver. Conclusions: The collected data provides expected ranges for CTDIvol and DLP for technologists to use in evaluating CT scans to look for anomalies which may be caused by changes in scan protocols or incorrect protocol or scan parameter selection. This will allow us to set up a quality assurance program to detect, report and correct such errors as they occur.

Comprehensive analysis of the Cramer–Rao bounds for magnetic resonance temperature change measurement in fat–water voxels using multi-echo imaging

The aim of this paper is to characterize the noise propagation for MRI temperature change measurement with emphasis on finding the best echo time combinations that yield the lowest temperature noise. A Cramer-Rao lower-bound (CRLB) calculation was used to estimate the temperature noise for a model of the MR signal in fat-water voxels. The temperature noise CRLB was then used to find a set of echo times that gave the lowest temperature change noise for a range of fat-water frequency differences, temperature changes, fat/water signal ratios, and T2* values. CRLB estimates were verified by Monte Carlo simulation and in phantoms using images acquired in a 1.5 T magnet. Results show that regions exist where the CRLB predicts minimal temperature variation as a function of the other variables. The results also indicate that the CRLB values calculated in this paper provide excellent guidance for predicting the variation of temperature measurements due to changes in the signal parameters. For three echo scans, the best noise characteristics are seen for TE values of 20.71, 23.71, and 26.71 ms. Results for five and seven echo scans are also presented in the text. The results present a comprehensive analysis of the effects of different scan parameters on temperature noise, potentially benefiting the selection of scan parameters for clinical MRI thermometry.

SU‐GG‐I‐122: ACR MRI Accreditation Equipment Performance Evaluation for Various Scanner Settings

Purpose: ACR MRI Accreditation program was created a decade ago for assessing performance by various facilities. Accreditation was voluntary at that time. Recently many stand‐alone MRI imaging centers/clinics seek accreditation because it is now mandatory by some insurance companies. For ACR MRI physics survey/system performance evaluation, it is closely correlated with the equipment performance. It is a challenging task to survey a variety of magnets in different field strength, configurations, and with many software versions/optional packages. The purpose of this work is to summarize ACR MR system evaluation and ACR phantom test experience. Method and Materials: GE, Siemens, Philips, and Hitachi's MRI magnets, in fixed or mobile setup, ranging from 0.3T, 0.7T, 1.0T, 1.5T, to 3.0T are surveyed. Both ACR and site T1/T2 scan protocols are used. Results: It is found that when an MRI scanner is properly maintained, geometric accuracy, slice thickness accuracy, and percent signal ghosting is usually within the limit regardless of fixed or mobile setup, or field strength of the magnet. However, intensity uniformity and low contrast detectability are most demanding for very low field (&lt;0.5T) and 3.0T magnets. At a low magnetic field, it is caused by low signal to noise ratio. For a 3.0T magnet, it is caused by low RF penetration at high field strength, and a much higher acceptable limit for low contrast detectability. In some cases, site protocol for T1 and T2 pulse sequences is required to pass the ACR phantom test. Conclusion: The ACR MRI phantom testing items are designed for different scanner performance criteria. When a testing result is out of the ACR acceptable limit, it is important for the physicist to recognize whether the phantom is not setup properly, or it is caused by scan parameter selection, or a service call is necessary.

The influence of patient centering on CT dose and image noise

Although x-ray intensity shaping filters (bowtie filters) have been used since the introduction of some of the earliest CT scanner models, the clinical implications on dose and noise are not well understood. To achieve the intended dose and noise advantage requires the patient to be centered in the scan field of view. In this study we explore the implications of patient centering in clinical practice. We scanned various size and shape phantoms on a GE LightSpeed VCT scanner using each available source filter with the phantom centers positioned at 0, 3, and 6 cm below the center of rotation (isocenter). Surface doses were measured along with image noise over a large image region. Regression models of surface dose and noise were generated as a function of phantom size and centering error. Methods were also developed to determine the amount of miscentering using a scout scan projection radiograph (SPR). These models were then used to retrospectively evaluate 273 adult body patients for clinical implications. When miscentered by 3 and 6 cm, the surface dose on a 32 cm CTDI phantom increased by 18% and 41% while image noise also increased by 6% and 22%. The retrospective analysis of adult body scout SPR scans shows that 46% of patients were miscentered in elevation by 20-60 mm with a mean position 23 mm below the center of rotation (isocenter). The analysis indicated a surface dose penalty of up to 140% with a mean dose penalty of 33% assuming that tube current is increased to compensate for the increased noise due to miscentering. Clinical image quality and dose efficiency can be improved on scanners with bowtie filters if care is exercised when positioning patients. Automatically providing patient specific centering and scan parameter selection information can help the technologist improve workflow, achieve more consistent image quality and reduce patient dose.

SU‐FF‐I‐29: Optimizing Radiation Dose and Image Quality in a Multi‐Detector Computed Tomography

Purpose: The study was carried out to find optimal scanning parameters for an MDCT at Ramathibodi hospital. Method and materials: Two types of phantom were employed to assess image quality and standard ionization chamber was used to measure radiation dose. Tube current, slice thickness, pixel size and pitch were varied from routine techniques to evaluate factors affecting image quality (spatial resolution, contrast detectability and image noise) and dose (CTDIair) with aim of optimization. Results: From our study showed that, optimization of radiation dose and image quality could be achieved by proper selection of scanning parameters. Reduction of tube current could be made 22 – 28%, pitch could be doubled from 0.75 to 1.5 (50% dose reduction) in slice thickness less than 7.5 mm without any significant effects on noise and contrast. In examinations that do not require high spatial resolution, larger pixel size could be made and could result in 15 – 17% dose reduction. Conclusions: We concluded from our study that, optimal scanning parameters were 115, 105, 150 and 170 mA for head (above/below posterior fossa) and abdomen (pre‐ and post‐ contrast) protocols, respectively. Slice thickness should be made thinnest possible before the penumbra dose penalty becomes significant. Pitch and pixel size should be selected based on clinical requirements.

SU‐FF‐I‐34: Radiation Dose in Cardiovascular Computed Tomography

Purpose: To assess the effective dose delivered to patients undergoing cardiovascular CT examinations at one institution. To highlight how adjustment of scan parameters to compensate for body habitus affects the CT dose index (CTDI), and how variations in CTDI and scan length combine to deliver a wide range of estimated effective dose. To evaluate the ability of manual scan parameter selection based on perceived patient size to maintain consistent image quality. Method and Materials: CT scan protocol parameters including kV, effective mAs, scan length, scan time, CTDIvol, dose length product (DLP), and effective dose were collected or calculated for cardiovascular CT examinations performed on a Philips Brilliance 64 scanner from Oct 2006 – March 2007. The effect of parameter selection on CTDIvol and effective dose was measured. Clinical factors were analyzed to determine the major contributors to CTDI and scan length, and thus to effective dose. Image contrast, noise and contrast‐to‐noise ratio were measured on clinical images to evaluate the ability of manual selection of kVp and mAs to compensate for body habitus and achieve consistent image quality. Results: The scan length in this patient population was 193.6 +/− 29 mm (range 125.6 – 279.2 mm). Effective dose measured 16.9 +/− 5.5 mSv (range 8.7 – 31.3 mSv). When the aorta and pulmonary arteries are also evaluated in “triple rule‐out” studies, scan length and thus effective dose tend to increase compared with simple coronary angiography. Image noise and contrast to noise ratio can be stabilized by adjusting kVp and mAs per slice based on patient size. Conclusions: Effective dose in CT depends linearly on both CTDIvol and scan length. Both of these factors can vary widely in cardiovascular CT, resulting in the potential for effective dose exceeding 30 mSv.

Estimation of effective doses to adult and pediatric patients from multislice computed tomography: A method based on energy imparted

The purpose of this study is to provide a method and required data for the estimation of effective dose (E) values to adult and pediatric patients from computed tomography (CT) scans of the head, chest abdomen, and pelvis, performed on multi-slice scanners. Mean section radiation dose (dm) to cylindrical water phantoms of varying radius normalized over CT dose index free-in-air (CTDIF) were calculated for the head and body scanning modes of a multislice scanner with use of Monte Carlo techniques. Patients were modeled as equivalent water phantoms and the energy imparted (epsilon) to simulated pediatric and adult patients was calculated on the basis of measured CTDI(F) values. Body region specific energy imparted to effective dose conversion coefficients (E/epsilon) for adult male and female patients were generated from previous data. Effective doses to patients aged newborn to adult were derived for all available helical and axial beam collimations, taking into account age specific patient mass and scanning length. Depending on high voltage, body region, and patient sex, E/epsilon values ranged from 0.008 mSv/mJ for head scans to 0.024 mSv/mJ for chest scans. When scanned with the same technique factors as the adults, pediatric patients absorb as little as 5% of the energy imparted to adults, but corresponding effective dose values are up to a factor of 1.6 higher. On average, pediatric patients absorb 44% less energy per examination but have a 24% higher effective dose, compared with adults. In clinical practice, effective dose values to pediatric patients are 2.5 to 10 times lower than in adults due to the adaptation of tube current. A method is provided for the calculation of effective dose to adult and pediatric patients on the basis of individual patient characteristics such as sex, mass, dimensions, and density of imaged anatomy, and the technical features of modern multislice scanners. It allows the optimum selection of scanning parameters regarding patient doses at CT.