Assessment of patient dose and optimization levels in chest and abdomen CR examinations at referral hospitals in Tanzania.

The aim of this study was to evaluate the radiation doses to patient during chest and abdomen CR examinations, and assess the related level of optimization at five referral hospitals in Tanzania. The international code of practice for dosimetry in diagnostic radiology was applied to determine the entrance surface air kerma (ESAK) to patients. The level of optimization was assessed from low-contrast objects scores of phantom images at different exposures. The results show that mean ESAK varied from 0.16 to 0.37 mGy for chest PA and from 2 to 6 mGy for abdomen AP. Assuming similar patient and phantom attenuations, the optimization performed at all facilities was consistent with phantom evaluations in terms of tube potential settings in use. However, all facilities seemed to operate at higher tube load values above 5 mAs for chest examination, which can lead to unnecessary patient doses. Inadequate initial training on CR technology explains in large proportion the inappropriate use of exposure parameters.

ESTIMATION OF PATIENT RADIATION DOSES FROM MULTI-DETECTOR COMPUTED TOMOGRAPHY ANGIOGRAPHY PROCEDURES IN TANZANIA.

The aim of the present study was to estimate the volume CT dose index (CTDIvol), dose length product (DLP) and effective dose (ED) to patients from five multi-detector computed tomography angiography (MDCTA) procedures: brain, carotid, coronary, entire aorta and lower limb from four medical institutions in Tanzania; to compare these doses to those reported in the literature, and to compare the data obtained with ICRP 103 and Monte Carlo software. The radiation doses for 217 patients were estimated using patient demographics, patient-related exposure parameters, the geometry of examination and CT-Expo V 2.4 Monte Carlo-based software. The median values of the CTDIvol, DLP and ED for MDCTA procedures of the brain and carotids were 36.8 mGy, 1481.0 mGy∙cm and 5.2 mSv, and 15.9 mGy, 1224.0 mGy∙cm and 7.8 mSv, respectively; while for the coronary, entire aortic, and lower limbs were 49.4 mGy, 1493.0 mGy∙cm and 30.6 mSv; 16.2 mGy, 2287.0 mGy∙cm and 41.1 mSv; and 6.4 mGy, 1406.0 mGy∙cm and 10.5 mSv, respectively. The ratio of the maximum to minimum ED values to individual patients across the four medical centers were 41.4, 11.1, 4.6, 9.5 and 37.4, respectively, for the brain, carotid, coronary, entire aortic and lower limb CT angiography procedures. The mean values of CTDIvol, DLP and ED in the present study were typically higher than the values reported from Kenya, Korea and Saudi Arabia. The 75th percentile values of the DLP were above the preliminary diagnostic references levels proposed by Kenya, Switzerland and Korea. The observed wide range of examination scanning protocols and patient doses for similar MDCTA procedures within and across hospitals; and the observed relatively high patient doses compared to those reported in the literature, call for the need to standardize scanning protocols and optimise patient dose from MDCTA procedures.

Application of European protocol in the evaluation of contrast-to-noise ratio and mean glandular dose for two digital mammography systems.

The performance of two digital mammography systems, Agfa CR75 and CRMM3 computed radiography (CR) and IMS Giotto MD direct digital radiography (DR), was assessed by applying a method recommended in the European protocol for quality control in mammography screening. The contrast-to-noise ratio (CNR) and mean glandular dose (MGD) values were measured and contrast detail (CD) analysis was performed. The CNRs for system CR were 21.9, 12.9, 9.5, 8.8, 7.4, 5.5 and 4.4 for 2, 3, 4, 4.5, 5, 6 and 7-cm polymenthylmethacrylate (PMMA) thickness, respectively. The respective CNRs for system DR were 10.4, 8.8, 6.3, 7.3, 7.2, 6.4 and 6.54. For the same phantom thickness sequence, the MGDs were 0.7, 1.1, 1.3, 1.6, 1.9, 2.5 and 3.4 mGy for system CR, whereas they were 0.7, 1.2, 1.1, 1.3, 1.8, 3.5 and 3.9 mGy for system DR. The CNR and MGD results satisfactorily correlate with CD analysis results. The MGD values compare well with the values recommended in the European protocol. Despite being simple, CNR and MGD can provide an effective system for performance assessment and constancy checks for related optimisations.

Use of lead shields for radiation protection of superficial organs in patients undergoing head CT examinations.

Head computed tomography examinations are often accompanied with unnecessary irradiation of superficial organs that are rarely the main target for the investigation. The aim of this work is to demonstrate that lead shields could be effectively used to protect superficial organs without compromising image quality where superficial organ itself is not a target and that the irradiation of the superficial organ is unavoidable. The objective was achieved by first assessing the image quality using phantom measurements made with and without lead shielding in order to determine optimal shielding thickness for patient applications. The entrance surface doses (ESDs) to superficial organs of sixty patients were measured using LiF-thermoluminescent dosemeters without, with one layer, or with two layers of lead shields. Phantom studies demonstrated that the use of modified lead shields of up to 0.25 mm thickness could be used without significant effect on the image quality for central and posterior regions. In these studies, lead shields of 0.25 mm thickness reduce the ESDs to the lens of the eyes and thyroid by 44 and 51%, respectively. The image quality reduction by eye shields was significant to the anterior (i.e. orbital) region but marginal to the central and posterior regions (cerebrum). In view of the above, the use of modified lead shields could reduce the dose to the superficial organs considerably without significantly compromising image quality.

PRELIMINARY INVESTIGATION OF RADIATION DOSE TO PATIENTS FROM CARDIOVASCULAR INTERVENTIONAL PROCEDURES IN TANZANIA.

Although contemporary cardiac X-ray exams are typically set so benefits outweighs the risk, the growing use and increasing complexity of the cardiovascular interventional radiological (CVIR) procedures does increase the risk of radiation-related tissue effects and stochastic effects to the individual patients and the population. In view of these radiological concerns there is a need to investigate factors that influence the doses received by the patients and enable optimisation needed. The air kerma area product (KAP), cumulative air kerma (CAK) and fluoroscopy time (FT) to patients from two major CVIR procedures: coronary angiography (CA) and percutaneous coronary interventions (PCI), were obtained from two major hospitals in Tanzania. The CAK and KAP were determined using ionisation chambers equipped in each angiographic unit. The median values of the KAP, CAK and FT for the CA procedures were 37.8 Gy cm2, 425.5 mGy and 7.6 min, respectively, while for the PCI were 86.5 Gy cm2, 1180.3 mGy and 19.0 min, respectively. The overall differences among individual KAP, CAK and FT values across the two hospitals investigated differed by factors of up to 33.5, 58.7 and 26.3 for the CA, while for the PCI procedures differed by factors of up to 10.9, 25.3 and 13.8, respectively. The mean values of KAP and FT for both CA and PCI were mostly higher than those reported values for Ireland, Belgium, Greece, France, China and Australia. The third quartiles of the KAP, CAK and FT for both CA and PCI were relatively above the preliminary diagnostic reference levels proposed by the IAEA, DIMOND III and SENTINEL. The observed substantial variations of mean values of technical parameters and patient doses (KAP, CAK and FT values) observed for the CA and PCI procedures inter and intra-hospitals were mainly explained by the complexity of the CVIR procedures, the nature of pathology, patient-specific characteristics, the variation in levels of skills and experiences among IC personnel, and the different procedural protocols employed among interventional cardiologists and hospitals. The observed great variations of procedural protocols and patient doses within and across the hospitals and relative higher dose than reported values from the literature call for the need to optimise radiation dose to patient from IC procedures.

Survey of Effective Doses to Patients Undergoing Contrast-Based X-ray Fluoroscopy Procedures in Tanzania.

The aim of this study was to assess the radiation burden imparted to patients from contrast-based X-ray fluoroscopy procedures in Tanzania. The effective doses (EDs) to patients from five contrast-based fluoroscopy procedures were obtained from four hospitals. The ED was estimated using the knowledge of the patient characteristics, patient-related exposure parameters, measurements of air kerma area product and PCXCM software. The median EDs for the barium swallow (BS), barium meal (BM), barium enema (BE), hysterosalpingography (HSG) and retrograde urethrography (RUG) were 0.50, 1.43, 2.83, 0.65 and 0.59 mSv, respectively. The median ED per hospital for the BS and BM procedures varied by factors of up to 9.9 and 4.2, respectively, while for the BE, HSG and RUG varied by factors of up to 2.3, 2.4 and 4.3, respectively. The overall differences between individual EDs across the four hospitals varied by factors of up to 53, 58.9 and 11.4 for the BS, BM and BE, respectively, while for the HSG and RUG differed by factors of up to 22 and 46.7, respectively. The mean EDs in this study were mostly lower than reported values from Spain, the UK, Ghana and Greece, while slightly higher than those reported from India. The observed wide variations of procedural protocols and patient doses within and across the hospitals; and the observed high patient doses in this study relative to those from the literature call for the need to standardize procedural protocols and optimize contrast-based fluoroscopy procedures.

Initial Investigation of Factors Influencing Radiation Dose to Patients Undergoing Barium-Based Fluoroscopy Procedures in Tanzania.

The aim of this study was to investigate the nature and causes of radiation dose imparted to patients undergoing barium-based X-ray fluoroscopy procedures in Tanzania and to compare these doses to those reported in the literature from other regions worldwide. The air kerma area product (KAP) to patient undergoing barium investigations of gastrointestinal tract system was obtained from four consultant hospitals. The KAP was determined using a flat transparent transmission ionization chamber. Mean values of KAP for barium swallow (BS), barium meal (BM) and barium enema (BE) were 2.79, 2.62 and 15.04 Gy cm2, respectively. The mean values of KAP per hospital for the BS, BM and BE procedures varied by factors of up to 7.3, 1.6 and 2.0, respectively. The overall difference between individual patient doses across the four consultant hospitals investigated differed by factors of up to 53, 29.5 and 12 for the BS, BM and BE procedures, respectively. The majority of the mean values of KAP was lower than the reported values for Ghana, Greece, Spain and the UK, while slightly higher than those reported for India. The observed wide variation of KAP values for the same fluoroscopy procedure within and among the hospitals was largely attributed to the dynamic nature of the procedures, the patient characteristics, the skills and experience of personnel, and the different examination protocols employed among hospitals. The observed great variations of procedural protocols and patient doses within and across the hospitals call for the need to standardize examination protocols and optimize barium-based fluoroscopy procedures.

Current status of patient radiation doses from computed tomography examinations in Tanzania.

The aim of this study was to assess the magnitude of radiation dose imparted to patients undergoing CT (computed tomography) examinations in Tanzania. The effective doses to patients undergoing five common CT examinations were obtained from eight health centres. The doses to patients were estimated using measurements of CTDI, exposure-related parameters and the CTDOSE software based on NRPB conversion factors. The mean effective doses in Tanzania for CT examinations of head, lumbar spine, chest, abdomen and pelvis were 2.2+/-0.9, 5.4+/-2.3, 12.2+/-3.4, 15.3+/-6.0 and 13.4+/-7.3 mSv, respectively. The mean effective doses and the variations in dose between hospitals in Tanzania were mostly comparable with reported values in the literature for six different countries from Europe. The observed wide variation in mean effective dose for similar CT examination among hospitals was largely influenced by different CT scanning protocols employed among hospitals. In view of the observed causes of variation in patient doses, it was concluded that further studies are needed to investigate the methods that can reduce dose to patients without affecting image quality.

Subtraction of Compton-scattered photons in single-photon emission computerized tomography.

A technique for scatter correction in single photon emission computerized tomography (SPECT) is described. The method is based on "deconvolution" of scattered events from the measured profile data. The function defining the scatter distribution was determined from measurements with a line source in circular and rectangular water phantoms. The accuracy of the method was tested on a simple phantom simulating a SPECT investigation of the liver. The indicated ratio of the activity concentration in a photon-deficient area, 60 mm diameter in the "liver", relative to its surroundings, was 0.28/1 without scatter correction and 0.01/1 with the correction.

Assessment of scatter components in high-resolution PET: correction by nonstationary convolution subtraction.

UNLABELLED: This paper describes a new approach to determine individual scatter kernels and to use them for scatter correction by integral transformation of the projections. METHODS: Individual scatter components are fitted on the projections of a line source by monoexponentials. The position-dependent scatter parameters of each scatter components are then used to design non-stationary scatter correction kernels for each point in the projection. These kernels are used in a convolution-subtraction method which consecutively removes object, collimator and detector scatter from projections. This method is based on a model which assumes that image degradation results exclusively from Compton interactions of annihilation photons, thus neglecting further Compton interactions of object scatters with collimator and detector. RESULTS: Subtraction of the object scatter component improved contrast typical of what is obtained with standard convolution-subtraction methods. The collimator scatter component is so weak that it can be safely combined with object scatter for correction. Subtraction of detector scatter from images did not improve contrast because statistical accuracy is degraded by removing counts from hot regions while cold regions (background) remain unchanged. CONCLUSION: Subtraction of object and collimator scatter improves contrast only. The slight gain in image sharpness resulting from the subtraction of detector scatter does not justify removal of this component at the expense of sensitivity.

Nonstationary scatter subtraction-restoration in high-resolution PET.

UNLABELLED: Although removal of object scatter has been shown to improve both contrast and quantitation accuracy, subtraction of detector scatter leads to marginal contrast enhancement and negligible resolution recovery at the expense of reduced sensitivity and increased statistical noise. Since detector scatter has correct information about radioactivity but slightly erroneous information about source location, we suggest that this component should be restored to preserve sensitivity and improve resolution. METHODS: A scatter correction model that consecutively removes object scatter and restores detector scatter is proposed. The scatter components are processed in the spatial domain using nonstationary scatter kernels. The detector scatter restoration kernel is obtained by piecewise inversion in the Fourier space. The model was tested using line source and hot spot phantom measurements. RESULTS: Object scatter subtraction increased contrast substantively with no effect on resolution. Detector scatter restoration recovered resolution almost completely with modest contrast enhancement in small lesions. Spillover effects were reduced to less than 5% for hot spots > or = 3 x FWHM, at the expense of moderate noise amplification. CONCLUSION: While subtraction of object scatter is necessary for contrast enhancement and quantitation accuracy, restoration of detector scatter preserves sensitivity and improves quantitation accuracy by reducing spillover effects in high-resolution PET.

Generalized scatter correction method in SPECT using point scatter distribution functions.

A new two-dimensional (2-D) scatter correction technique in single photon emission computed tomography (SPECT) based on convolution or frequency filtering with a 2-D scatter distribution function is described. A scatter distribution function of the form A exp(-Br), has been derived from measurements of a point source in a water phantom. Both the amplitude A and the slope B of this function, were approximately invariant with source position except near phantom surface. The accuracy of the 2-D correction technique was compared with that of the previous one-dimensional (1-D) scatter correction technique. As could be expected the latter technique was shown to be less accurate due to its dependence on axial distribution of radioactivity. Phantom SPECT studies showed a clear superiority of the 2-D over the 1-D scatter correction in quantitative imaging. Images derived from clinical studies of regional bloodflow with 99mTc-HM-PAO and liver uptake showed significant contrast improvement by both techniques.

Energy dependence of scatter components in multispectral PET imaging.

High resolution images in PET based on small individual detectors are obtained at the cost of low sensitivity and increased detector scatter. These limitations can be partially overcome by enlarging discrimination windows to include more low-energy events and by developing more efficient energy-dependent methods to correct for scatter radiation from all sources. The feasibility of multispectral scatter correction was assessed by decomposing response functions acquired in multiple energy windows into four basic components: object, collimator and detector scatter, and trues. The shape and intensity of these components are different and energy-dependent. They are shown to contribute to image formation in three ways: useful (true), potentially useful (detector scatter), and undesirable (object and collimator scatter) information to the image over the entire energy range. With the Sherbrooke animal PET system, restoration of detector scatter in every energy window would allow nearly 90% of all detected events to participate in image formation. These observations suggest that multispectral acquisition is a promising solution for increasing sensitivity in high resolution PET. This can be achieved without loss of image quality if energy-dependent methods are made available to preserve useful events as potentially useful events are restored and undesirable events removed.

Position-dependent scatter response functions: will they make a difference in SPECT conducted with homogeneous cylindrical phantoms?

This paper explains why it is possible to perform accurate quantitative SPECT when scatter correction is based on stationary and non-stationary scatter functions. This is achieved by comparing the variations of scatter parameters as a function of phantom thickness. The results show that the decrease of scatter fraction with phantom thickness and the decrease of values of scatter kernel inside the field of view are about equal. The deviation of the position-dependent slope from the average value is small for central distributions. These observations explain why estimations of scatter projection by non-stationary convolution and by stationary convolution are comparable when SPECT measurements are conducted with uniform cylindrical phantoms. It is concluded that investigations on the perceived superiority of non-stationary over stationary scatter subtraction in SPECT should be conducted with elliptic phantoms that deviate appreciably from cylindrical shape.

Pre-processing variance reducing techniques in multispectral positron emission tomography.

Stochastic fluctuations and systematic errors severely restrict the potential of multispectral acquisition to improve scatter correction by energy-dependent processing in high-resolution positron emission tomography (PET). To overcome this limitation, three pre-processing approaches which reduce stochastic fluctuations and systematic errors without degrading spatial resolution were investigated: statistical variance was reduced by smoothing acquired data in energy space, systematic errors due to nonuniform detector efficiency were minimized by normalizing the data in the spatial domain and the overall variance was further reduced by selecting an optimal pre-processing sequence. Selection of the best protocol to reduce stochastic fluctuations entailed comparisons between four smoothing algorithms (prior constrained (PC) smoothing, weighted smoothing (WS), ideal low-pass filtering (ILF) and mean median (MM) smoothing) and permutations of three pre-processing procedures (smoothing, normalization and subtraction of random events). Results demonstrated that spectral smoothing by WS, ILF and MM efficiently reduces the statistical variance in both the energy and spatial domains without observable spatial resolution loss. The ILF algorithm was found to be the most convenient in terms of simplicity and efficiency. Regardless of the position of subtraction of randoms in the sequence, reduction of the systematic errors by normalization followed by spectral smoothing to suppress statistical noise produced the best results. However, subtraction of random events first in the sequence reduces computation load by half since the need to pre-process this distribution before subtraction is removed. In summary, normalizing data in the spatial domain and smoothing data in energy space are essential steps required to reduce systematic errors and statistical variance independently without degrading spatial resolution of multispectral PET data.

Some physical factors influencing the accuracy of convolution scatter correction in SPECT.

Some important physical factors influencing the accuracy of convolution scatter correction techniques in SPECT are presented. In these techniques scatter correction in the projection relies on filter functions, QF, evaluated by Fourier transforms, from measured scatter functions, Qp, obtained from point spread functions. The spatial resolution has a marginal effect on Qp. Thus a single QF can be used in the scatter correction of SPECT measurements acquired with the low energy high resolution or the low energy general purpose collimators and over a wide range of patient-collimator distances. However, it is necessary to examine the details of the shape of point spread functions during evaluation of Qp. QF is completely described by scatter amplitude AF, slope BF and filter sum SF. SF is obtained by summation of the values of QF occupying a 31 x 31 pixels matrix. Regardless of differences in amplitude and slope, two filter functions are shown to be equivalent in terms of scatter correction ability, whenever their sums are equal. On the basis of filter sum, the observed small influence of ellipticity on QF implies that an average function can be used in scatter correcting SPECT measurements conducted with elliptic objects. SF is shown to increase with a decrease in photon energy and with an increase in window size. Thus, scatter correction by convolution may be severely hampered by photon statistics when SPECT imaging is done with low-energy photons. It is pointless to use unnecessarily large discriminator windows, in the hope of improving photon statistics, since most of the extra events acquired will eventually be subtracted during scatter correction. Regardless of the observed moderate reduction in SF when a lung-equivalent material replaces a portion of a water phantom, further studies are needed to develop a technique that is capable of handling attenuation and scatter corrections simultaneously. Whenever superficial and inner radioactive distributions coexist the observed reduction of SF close to the phantom surface indicates that scatter correction of such distributions has to rely on two distinct filter functions. Corrections based on a surface function produce accurate results in the superficial region, while the central distributions are substantially overestimated. Surface radioactive distributions introduce appreciable errors in the determination of central distributions when corrections are based on central filter function. This function introduces a reduction of about 40% in the measured surface concentration.

The relative contributions of scatter and attenuation corrections toward improved brain SPECT quantification.

Mounting evidence indicates that scatter and attenuation are major confounds to objective diagnosis of brain disease by quantitative SPECT. There is considerable debate, however, as to the relative importance of scatter correction (SC) and attenuation correction (AC), and how they should be implemented. The efficacy of SC and AC for 99mTc brain SPECT was evaluated using a two-compartment fully tissue-equivalent anthropomorphic head phantom. Four correction schemes were implemented: uniform broad-beam AC, non-uniform broad-beam AC, uniform SC + AC, and non-uniform SC + AC. SC was based on non-stationary deconvolution scatter subtraction, modified to incorporate a priori knowledge of either the head contour (uniform SC) or transmission map (non-uniform SC). The quantitative accuracy of the correction schemes was evaluated in terms of contrast recovery, relative quantification (cortical:cerebellar activity), uniformity ((coefficient of variation of 230 macro-voxels) x 100%), and bias (relative to a calibration scan). Our results were: uniform broad-beam (mu = 0.12 cm(-1)) AC (the most popular correction): 71% contrast recovery, 112% relative quantification, 7.0% uniformity, +23% bias. Non-uniform broad-beam (soft tissue mu = 0.12 cm(-1)) AC: 73%, 114%, 6.0%, +21%, respectively. Uniform SC + AC: 90%, 99%, 4.9%, +12%, respectively. Non-uniform SC + AC: 93%, 101%, 4.0%, +10%, respectively. SC and AC achieved the best quantification; however, non-uniform corrections produce only small improvements over their uniform counterparts. SC + AC was found to be superior to AC; this advantage is distinct and consistent across all four quantification indices.

A survey of background radiation dose rates and radioactivity in Tanzania.

Potential terrestrial sources of naturally occurring elevated radiation levels have been identified in Tanzania. Thus, efforts are currently being undertaken to create a natural radiation database, in the form of a radiation level map of natural radioactivity, to be used to assess the associated radiation risk to public and workers. Background radiation dose rate was determined with thermoluminescent dosimeters for 7 y (1993-1999) in five stations. The average background radiation dose rates for these stations were as follows: Tropical Pesticides Research Institute (TPRI) (102 +/- 7 nGy h(-1)), Same (98 +/- 2 nGy h(-1)), Namanga (98 +/- 5 nGy h(-1)), University of Dar Es Salaam (99 +/- 2 nGy h(-1)), and Kilimanjaro Christian Medical Center (121 +/- 3 nGy h(-1)). These stations were found convenient from an economic point of view since the project has no funds to cover wider and/or more remote areas in Tanzania. For the sake of comparison, similar measurements were made for the same period at Minjingu phosphate mine. The mine was one of the suspected areas with elevated levels of natural radioactivity. The radiation dose rate measured in this mine was about fourteen times higher (1,415 +/- 28 nGy h(-1)) than the average value obtained in northern Tanzania (98 nGy h(-1)). The high average activity levels of phosphate (5760 +/- 107 Bq kg(-1) for 261Ra, 497 +/- 5 Bq kg(-1) for 228Ra, 350 +/- 6 Bq kg(-1) for 228Th, and 280 +/- 5 Bq kg(-1) for 40K) and radiation dose rate recorded show that Minjingu phosphate mine has higher values than the highest radioactivity in phosphate compiled by the United Nations Scientific Committee on the Effect of Atomic Radiation. In view of these findings, a comprehensive risk-management strategy for reduction of radiation risk to the public and mine workers should be put in place. Efforts are currently being made to seek support to improve the background radiation database for subsequent assessment of radiation risk to miners and the societies in the vicinity of these mines in Tanzania.

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.