Optimisation of radiation dose and image quality in mobile neonatal chest radiography

PurposeTo optimise the radiation dose and image quality for chest radiography in the neonatal intensive care unit (NICU) by increasing the mean beam energy.MethodsTwo techniques for the acquisition of NICU AP chest X-ray images were compared for image quality and radiation dose. 73 images were acquired using a standard technique (56 kV, 3.2 mAs and no additional filtration) and 90 images with a new technique (62 kV, 2 mAs and 2 mm Al filtration). The entrance surface air kerma (ESAK) was measured using a phantom and compared between the techniques and against established diagnostic reference levels (DRL). Images were evaluated using seven image quality criteria independently by three radiologists. Images quality and radiation dose were compared statistically between the standard and new techniques.ResultsThe maximum ESAK for the new technique was 40.20 μGy, 43.7% of the ESAK of the standard technique. Statistical evaluation demonstrated no significant differences in image quality between the two acquisition techniques.ConclusionsBased on the techniques and acquisition factors investigated within this study, it is possible to lower the radiation dose without any significant effects on image quality by adding filtration (2 mm Al) and increasing the tube potential. Such steps are relatively simple to undertake and as such, other departments should consider testing and implementing this dose reduction strategy within clinical practice where appropriate.     

A phantom approach to find the optimal technical parameters for plain chest radiography

A simple approach based on phantom measurements is proposed in this study to find the filtration, tube potential and antiscatter device that are optimal in respect of patient dose and image quality, at constant film-screen combination, film processing and viewing conditions. An original quasi-anthropomorphic chest phantom was exposed with 18 different beam qualities and three antiscatter devices. The entrance surface dose, organ doses and effective dose were estimated for each radiograph. The image quality was compared using two objective quality indexes, a contrast index and a scatter fraction, as well as two subjective indexes, a low contrast visualization index and a high contrast visualization index. It was found that for this X-ray unit, routinely using a 7:1 antiscatter grid, the optimal imaging technique is added filtration of 0.1 mm Cu+1 mm Al at a tube potential 100 kVp. Using a 25 cm air gap instead of the grid allows the tube potential to be increased to the upper limit of 120 kVp for this unit. The entrance surface dose of 0.075 mGy at 120 kVp with an air gap is less than half the value of the same quantity with a grid at 100 kVp and is significantly below the European reference level of 0.3 mGy. This phantom method, comprising both objective measurements and subjective estimation, is suitable for dose-image quality optimization in a clinical environment.     

Air gap technique for digital subtraction angiography of the extracranial carotid arteries

The technique of applying an air gap between the patient and the x-ray detector reduces scattered radiation from the patient's neck sufficiently to allow performance of DSA of the extracranial carotid arteries with the antiscatter grid removed. When compared with the conventional grid technique, air gap allows 25 to 88% reduction of mA without increasing the kVp or exposure time and without loss of spatial resolution or diagnostic image quality. These considerable patient radiation-exposure savings can be implemented on DSA systems that use ordinary under-table x-ray tube fluoroscopic equipment without the purchase of additional hardware.     

Evaluating the use of higher kVp and copper filtration as a dose optimisation tool in digital planar radiography

IntroductionTo identify the potential of beam hardening techniques, specifically the use of higher kilo voltage (kV) and copper (Cu) filtration, to optimise digital planar radiographic projections. The study assessed the suitability of such techniques in radiation dose reductions while maintaining diagnostic image quality for four common radiographic projections: antero-posterior (AP) abdomen, AP-knee, AP-lumbar spine, and lateral lumbar spine.MethodsAnthropomorphic phantom radiographs were obtained at varying kVp (standard kVp, +10 kVp, and +20 kVp) and varying Cu filtration thickness (0 mm, 0.1 mm, and 0.2 mm Cu). The Dose Area Product (DAP), mAs and time (s) were recorded as an indication of the emitted radiation dose. Image quality was assessed objectively via Contrast-Noise-Ratio (CNR) calculations and subjectively via Visual Grading Analysis (VGA) performed by radiographers and radiologists.ResultsOptimised exposure protocols were established for the AP-abdomen (100 kVp with 0.2 mm Cu), AP-knee (85 kVp, and 0.1 mm Cu), AP-lumbar spine (110 kVp and 0.2 mm Cu), and lateral lumbar spine (110 kVp and 0.2 mm Cu). This strategy resulted in respective DAP reductions of 71.98%, 62.50%, 64.51% and 71.85%. While CNR values decreased as beam hardening techniques were applied, VGA demonstrated either a lack of statistical variation or improved image quality between the standard and the optimised exposure protocols.ConclusionsDAP reductions without compromising image quality can be achieved through beam hardening for the AP-abdomen, AP-knee, AP-lumbar spine, and lateral lumbar spine projections.Implications for practiceBeam hardening techniques should be considered as an optimisation strategy in medical imaging departments. Research into the applicability of this strategy for other radiographic projections is recommended.     

Multi-detector row spiral CT angiography of the thoracic outlet: dose reduction with anatomically adapted online tube current modulation and preset dose savings

PURPOSE: To evaluate image quality obtained with anatomically adapted online tube current modulation and preset minimum dose savings at multi-detector row spiral computed tomographic (CT) angiography of the thoracic outlet. MATERIALS AND METHODS: A total of 100 patients were evaluated for thoracic outlet arterial syndrome with spiral CT angiography (collimation, 4 x 1 mm; pitch, 1.75) both with and without dose reduction by means of anatomically adapted online tube current modulation and preset minimum dose savings. Preset minimum savings of 20% and of 32% were applied in two groups of 50 patients (groups 1 and 2). In each group, low-dose scanning was performed in 25 patients in the neutral position and in 25 patients after postural maneuver. Tube current-time product, noise, presence and quality of graininess and of linear streak artifacts on transverse CT scans, and diagnostic value of sagittal reformations and volume-rendered images were evaluated and recorded for each data set. chi2 test was used to compare frequencies; paired Wilcoxon rank test, to compare subjective and objective image quality scores. P <.05 indicated a significant difference. RESULTS: In group 1, mean tube current-time product was 3225 mAs for reference scans and 2101 mAs for low-dose scans (mean reduction, 35%; range, 27%-47%). In group 2, mean was 3070 mAs for reference scans and 2068 mAs for low-dose scans (mean reduction, 33%; range, 17%-38%). In group 1, no differences in frequencies of graininess and linear streaking or in noise level were found between images acquired with or without dose reduction. In group 2, no difference was found in noise level between low-dose and reference scans. On low-dose scans, moderate linear streaking was observed with lower frequency and moderate graininess was observed with higher frequency, but artifacts did not compromise image quality or prevent confident assessment of arterial diameter in the three compartments of the thoracic outlet. CONCLUSION: Online tube current modulation with a preset minimum dose saving of 20% allowed 35% reduction in mean tube current-time product, with no loss in image quality.     

Added copper filtration in digital paediatric double-contrast colon examinations: effects on radiation dose and image quality

Paediatric double-contrast barium enema examinations are usually performed at high tube voltage, 102–105 kV. The aim of this study was to investigate how much the effective dose to the child could be reduced by increasing the X-ray energy further by adding copper filter in the beam, and if this dose reduction could be achieved without endangering image quality. Organ doses to an anthropomorphic phantom simulating a 1-year-old child was measured using thermoluminescence dosimetry for assessment of the effective dose and this value was compared with the energy imparted which was obtained from kerma-area product measurements. To verify that the image quality achieved with this added filtration was still diagnostically acceptable, the study included 15 patient examinations. Since the increased X-ray energy will most probably affect low-contrast objects, image quality was also evaluated with two different phantoms containing low-contrast objects. Effective dose for a complete examination can be decreased 44 % and energy imparted 77 % when a 0.3-mm copper filter is inserted in the beam at tube voltage 102 kV. The patient study did not show any significant deterioration of image quality, whereas phantom measurements of contrast-detail resolution and signal-to-noise ratio was marginally impaired by the added copper filtration. This technique is now in clinical practice for paediatric colon examinations. Received 31 July 1996; Revision received 23 December 1996; Accepted 12 February 1997     

Contrast-detail phantom study for x-ray spectrum optimization regarding chest radiography using a cesium iodide-amorphous silicon flat-panel detector

RATIONALE AND OBJECTIVES: The purpose of this study evaluating a cesium iodide-amorphous silicon-based flat-panel detector was to optimize the x-ray spectrum for chest radiography combining excellent contrast-detail visibility with reduced patient exposure. MATERIALS AND METHODS: A Lucite plate with 36 drilled holes of varying diameter and depth was used as contrast-detail phantom. For 3 scatter body thicknesses (7.5 cm, 12.5 cm, 21.5 cm Lucite) images were obtained at 113 kVp, 117 kVp, and 125 kVp with additional copper filter of 0.2 and 0.3 mm, respectively. For each setting, radiographs acquired with 125 kVp and no copper filter were taken as standard of reference. On soft-copy displays, 3 observers blinded to the exposure technique evaluated the detectability of each aperture in each image according to a 5-point scale. The number of points given to all 36 holes per image was added. The scores of images acquired with filtration were compared with the standard images by means of a multivariate analysis of variance. Radiation burden was approximated by referring to the entrance dose and calculated using Monte Carlo method. RESULTS: All 6 evaluated x-ray spectra resulted in a statistically equivalent contrast-detail performance when compared with the standard of reference. The combination 125 kVp with 0.3 mm copper was most favorable in terms of dose reduction (approximately 33%). CONCLUSION: Within the constraints of the presented contrast-detail phantom study simulating chest radiography, the CsI/a-Si system enables an addition of up to 0.3 mm copper filtration without the need for compensatory reduction of the tube voltage for providing constant image quality. Beam filtration reduces radiation burden by about 33%.     

A comparison of fixed and variable kVp technique protocols for film-screen mammography

Mammographic image quality, contrast and dose for a variable tube potential (kVp) technique protocol for film-screen mammography have been investigated. In this protocol, the tube potential is increased for larger breast thicknesses. Comparisons were made with fixed kVp protocols, in which the tube potential is kept constant and the breast thickness compensated for by prolonging the exposure ("fixed kVp" protocol). All measurements were performed on a mammography unit with a molybdenum target and filter. Image quality was quantified by image contrast, image detail detection and the minimum detectable dimension of low contrast objects. It was demonstrated that for a compressed breast thickness of less than about 40 mm, varying the tube potential had a negligible effect upon dose but a significant effect upon image quality. For a compressed breast thickness greater than about 60 mm, the effect of the tube potential upon image quality was much reduced; however, the effect upon dose was significantly greater. The variable kVp protocol takes advantage of this feature to yield a significantly lower dose for thicker breasts with a small reduction in image quality, often only within experimental uncertainty. For an exposure under automatic exposure control, increasing the tube potential from 26 kVp to 30 kVp for a breast of a reference tissue composition (50% adipose and 50% glandular) with a compressed thickness of 60 mm reduced the mean glandular dose from 6 mGy to 3.9 mGy (-35%), but increased the minimum detectable dimension of a low contrast mass from 0.8 (+/- 0.1) mm to 1.1 (+/- 0.1) mm. Adopting a variable kVp protocol led to a median patient mean glandular dose per film of 2.7 mGy, nearly independent of compressed breast thickness. In our survey, the mean age of women presenting for mammography is younger and the mean compressed breast thickness is less than reported from screening centres. This suggests that there will be a higher proportion of denser, glandular tissue in the breasts incorporated within this survey than for surveys from screening centres. The clinical use of the variable kVp protocol allows the extraction from patient data of separate changes in breast composition which are due to patient age and breast thickness. It is concluded that the reference breast tissue composition is not an accurate representation of the women presenting at this centre.     

Optimisation of direct digital chest radiography using Cu filtration

PurposeTo assess the impact of additional Cu filtration with the DRX-1 detector in optimisation of adult chest radiography.MethodsA simulated anatomical phantom was imaged at different levels of Cu filtration (0 mm, 0.1 mm, 0.3 mm and 0.5 mm of Cu) at 120 kVp. Image quality was assessed using exposure index, conspicuity index, signal-to-noise ratio and pixel density. Dose area product (DAP) meter was used to measure dose; effective dose and risk of exposure induced cancer death (REID) were estimated using the PCXMC software 2.0.ResultsExposure index increased with increasing Cu thickness; 0.3 mm Cu filtration increased conspicuity index of simulated nodules, with a minimal decrease in signal-to-noise ratio, and pronounced decrease in pixel density. Patient doses were reduced by 20.7%, 36.6%, and 39.79% at 0.1 mm, 0.3 mm, and 0.5 mm levels of Cu filtration respectively.ConclusionAdditional beam filtration using 0.3 mm Cu filter with the DXR-1 detector reduced patient doses by 37% without decline in image quality.     

Skin sparing in interventional radiology: the effect of copper filtration

Complex and lengthy interventional radiological techniques have resulted in a number of patients developing skin reactions in recent years. To safeguard against these side effects, we have investigated the degree to which entrance skin dose can be reduced by inserting 0.18 mm and 0.35 mm copper filtration in the incident beam. The potential reduction was measured on a 22 cm water phantom for each of eight models of a fluoroscopy unit. Using the catheter laboratory fluoroscopy unit on which radiofrequency ablations are routinely performed, we assessed the relative effectiveness of adding filtration and increasing the kV:mA ratio. Image quality was subjectively assessed for diagnostic and therapeutic acceptability in two groups of 10 patients undergoing radiofrequency ablations, pacemaker insertions or electrophysiology studies. One of the groups was screened with 0.35 mm copper filtration in place and the other group acted as the control. Maximum patient skin dose proved difficult to measure directly because of the unpredictable dose pattern. This pattern was studied in four patients using a film method in conjunction with thermoluminescent dosemeters. Copper filtration 0.35 mm thick inserted in the beams of the eight fluoroscopy units produced a mean reduction in entrance dose to the phantom of 58% with a mean increase in tube loading of 29%. At 100 kV the increased loading on the X-ray tube was equivalent to increasing the anteroposterior separation of the patient by 2 cm. Measurements on the catheter laboratory unit showed that the tube voltage would need to be raised above the normal diagnostic range to obtain an equivalent entrance dose reduction without the filter. The blackening of films under the patients showed complex patterns, but the estimated skin doses were consistent with those predicted by the phantom experiments. All six cardiologists considered there to be insignificant detriment to image quality in the procedures investigated.     

Evaluation of routine examinations using automatic scan technique optimization for X-CT

Auto mA is a function that automatically controls tube current so as to stabilize image quality. To determine the applicability of this function to routine inspection work, an evaluation was carried out by two doctors in the department of radiology and five technicians in the department of diagnostic radiology using home-made phantoms and phantoms for low contrast resolution determination. The phantom experiment provided an almost constant level of SD values in each Auto mA mode tested, independent of scanning type, slice thickness, and phantom shape. In addition, nearly stable low contrast resolution was attained independent of phantom shape, e.g., circle and ellipse. The results suggest that stable image quality is available in the clinical stage for individual patients and regions, independent of the size and shape of targets. As for the evaluation of clinical images, the image quality requested by clinical operations at our hospital was attained even in the low dose mode that provides the lowest dose level. In addition, for variations in tube current values for photographing in individual regions, both sustained image uniformity and exposure reduction were found to be satisfactory in comparison with constant tube current.     

Optimization of image quality and patient dose in radiographs of paediatric extremities using direct digital radiography

Objective:

The purpose of this study was to evaluate the effect of beam quality on the image quality (IQ) of ankle radiographs of paediatric patients in the age range of 0–1 year whilst maintaining constant effective dose (ED).

Methods:

Lateral ankle radiographs of an infant foot phantom were taken at a range of tube potentials (40.0–64.5 kV_p) with and without 0.1-mm copper (Cu) filtration using a Trixell Pixium 4600 detector (Trixell, Morains, France). ED to the patient was computed for the default exposure parameters using PCXMC v. 2.0 and was fixed for other beam qualities by modulating the tube current-time product. The contrast-to-noise ratio (CNR) was measured between the tibia and adjacent soft tissue. The IQ of the phantom images was assessed by three radiologists and a reporting radiographer. Four IQ criteria were defined each with a scale of 1–3, giving a maximum score of 12. Finally, a service audit of clinical images at the default and optimum beam qualities was undertaken.

Results:

The measured CNR for the 40 kV_p/no Cu image was 12.0 compared with 7.6 for the default mode (55  0.1 mm Cu). An improvement in the clinical IQ scores was also apparent at this lower beam quality.

Conclusion:

Lowering tube potential and removing filtration improved the clinical IQ of paediatric ankle radiographs in this age range.

Advances in knowledge:

There are currently no UK guidelines on exposure protocols for paediatric imaging using direct digital radiography. A lower beam quality will produce better IQ with no additional dose penalty for infant extremity imaging.Long bones (arms and legs) and short bones (hands, wrists, feet and ankles) of the upper and lower extremities undergo endochondral ossification; a process by which hyaline cartilage is converted to bone. This process begins during early gestation and continues through puberty and into early adulthood until skeletal maturity (18–25 years) when all of the cartilage is replaced by bone. Therefore, in comparison with adults, paediatric bones are more porous and have wider Haversian canals in addition to containing a large amount of collagen and cartilage.¹ Extremity imaging of patients during infancy poses a unique challenge owing to the low intrinsic contrast during skeletal bone development. When considering optimization of extremities in this age range, an understanding of the unossified cartilaginous skeleton is essential.Extremity imaging at Evelina London Children''s Hospital (ELCH), London, UK, is undertaken through various routes of referral and clinical indicators, including trauma and orthopaedic imaging (the identification of fractures or other bony injuries), genetics (ossification/growth of the bones) and oncology. Perhaps the most significant in the context of this study is the referral of patients for skeletal survey imaging, which incorporates both genetic and non-accidental injury (NAI) pathways. With an increased demand for NAI imaging within the establishment, radiology consultants who report all the imaging undertaken in ELCH, identified some ankle imaging of infant patients (0–1 year old) as undiagnostic, with particular reference to reduced image contrast where it was felt that a loss of clinical features caused subsequent difficulty in making confident clinical decisions. Occasionally repeat imaging was requested, with radiographers adjusting their individual imaging parameters in pursuit of an image providing clarity between the soft tissue and bone regions within the image.Paediatric patients are more susceptible than adults to the damaging effects of ionizing radiations owing to more rapid cell division and a longer life expectancy.² The lack of inherent contrast in paediatric extremity imaging is therefore also met by a requirement for optimization of the imaging parameters to ensure the radiation dose to the patient is kept “as low as reasonable achievable” (ALARA).³ Optimization may also minimize the number of requests for repeat imaging, hence reducing the radiation dose and therefore risk to the paediatric patient. In the context of paediatric trauma,⁴ planar X-ray imaging is still considered to be the primary imaging investigation of choice owing to its ready availability and cost effectiveness. Additionally, the Royal College of Radiologists indicate that for focal bone pain in paediatrics, plain film imaging is recommended as the first line of investigation in the evidence-based guidelines “Making the best use of clinical radiology”;⁵ the standards upon which all referrals are subject to in terms of justification.In conventional screen–film radiography, a fixed detector dose is required to achieve the correct optical density and therefore produce a useable clinical image. European guidelines⁶ published in 1996 have influenced the setting of exposure parameters across the range of different radiographic views. This guidance covers some of the most frequent anatomical projections, including projections of the chest, skull, pelvis, full and segmental spine, abdomen and urinary tract. The general guidance recommends using a higher tube potential () for all radiographic exposures of paediatrics. For older tube-generator systems where the shortest exposure times are not possible, slight lowering of the tube potential and the use of additional filtration is recommended to achieve the required optical density. It states “The soft part of the radiation spectrum which is completely absorbed in the patient is useless for the production of the radiographic image and contributes unnecessarily to the patient dose”. There is evidence suggesting that a harder beam quality in screen–film radiology can result in a lower effective dose (ED) for projections including posteroanterior projections of the chest and anteroposterior (AP) projections of the abdomen.⁷ However, a potential consequence of this dose reduction is a negative effect on the image quality (IQ) as a harder beam results in reduced inherent image contrast as less of the X-ray photons in the spectrum interact via photoelectric absorption.^7,8The International Commission on Radiological Protection (ICRP) have identified the need for optimization and development of consistent protocols in paediatric digital radiology with active participation of staff from a wide range of disciplines.⁹ Direct digital radiography (DDR) is fundamentally different from screen–film radiography in that it has a different energy response and does not require a fixed detector dose, and images can be processed post exposure. Numerous studies have been completed comparing the clinical IQ of extremity radiographs between screen–film and computed radiography (CR)^10–12 and additionally looking at the possibility of dose reduction in skeletal imaging using amorphous silicon flat panel detectors.^13,14 However, there is little published evidence to confirm that current protocols are optimized for a wide range of X-ray projections, including extremity imaging.There have been some optimization studies completed in areas such as cardiac imaging using a flat panel detector¹⁵ and paediatric chest, abdomen and pelvis radiography using CR,¹⁶ but there is very little literature available on optimization in paediatric extremity imaging. Work by Hess and Neitzel¹⁷ questions the use of filtration and suggests tube potentials as low as 40 kV_p and the removal of any additional filtration can improve the IQ in extremity radiographs of very young patients whilst keeping a fixed ED. This is a phantom study that simulates a paediatric extremity using polymethyl methacrylate representing soft tissue and an aluminium strip representing bone. The study by Brosi et al¹⁶ also questions the benefit of additional copper (Cu) filtration, particularly for radiographic projections that exclude any radiosensitive organs from the primary beam. The study concludes that a reduction in entrance surface dose (ESD) owing to the Cu filtration is not accompanied by a reduction in the ED, which is a true measure of patient risk. An extremity of an infant represents very little attenuation of the beam and the dominant radiosensitive tissue in these projections is the bone marrow according to the ICRP report 103² tissue-weighting factors. For such small structures as the infant extremity, the ratio of the ED to ESD is relatively constant across the tube potential range and actually decreases slightly at the lower tube voltages.¹⁷Despite the possible benefits of DDR and the scope for optimization in paediatric extremity imaging, it is likely that the current protocols originate from a combination of the European guidance,⁶ manufacturer''s advice and local input from experience with screen–film and possibly CR systems. Moore et al¹⁸ highlight that the anatomically programmed radiography presets on equipment provided by manufacturers may not be appropriate for paediatric exposures. Image optimization in digital radiography requires collaboration between the range of professions associated with the clinical sites and, additionally, the equipment manufacturers. Successful collaboration should result in high-quality digital radiographs being consistently achieved, whilst ensuring automated anatomical programme presets are in keeping with the ALARA principle. The literature review completed as part of this study suggests clinical IQ of extremity radiographs could potentially be improved by lowering the beam quality without resulting in a dose penalty to the patient.Prior to this study, the local set-up for a lateral ankle exposure of a patient in the 0–1 year (infant) age range at ELCH was 55  and 0.1-mm Cu filtration. The aim of this article is to assess the effects of altering tube potential and filtration, with the object of improving contrast and overall IQ, whilst keeping the ED fixed. The intention is to verify the results of Hess and Brosi using an anthropomorphic phantom and audit of clinical images.     

Filters for radiation reduction: a comparison

Aluminum, yttrium, copper, and R-filters were evaluated with respect to effective beam energy, entrance radiation exposure to the skin, x-ray tube loading, and the quality of resultant radiographs. Since all filters yielded acceptable radiographs, a figure of merit was developed to determine which filter delivered the lowest entrance radiation exposure for the lowest increase in x-ray tube loading. The figure of merit indicated that the best results were obtained with the 0.1-mm Cu filter with 2 mm Al at 60-105 kVp and with the 0.2-mm Cu filter with 2 mm Al at 105-120 kVp. Cu filters produced radiographs with quality comparable to that of R- or Y filters. Cu filters are inexpensive alternatives to rare-earth filters and yielded a reduction in radiation exposure with less x-ray tube loading.     

A study of optimum radiographic conditions on chest examinations with computed radiology (CR) in conjunction with the offset balance of patient dose and image quality]

In a report of a nationwide survey on radiographic conditions of chest radiography in Japan, it was pointed out that the average entrance surface dose (ESD) of the computed radiography (CR) system was higher than that of the film-screen system. It seemed important that an objective index and criteria be established for dose reduction without a loss of image quality that would interfere with diagnostic observation. For this purpose, we investigated the properties of root of mean square (RMS) granularity, since it is a dominant factor in CR image quality and strongly depends on dose. The results indicated that RMS granularity showed little dependence on tube voltage when relative exposure was kept constant and that it decreased with the increment of exposure and approached a finite minimum value in a very high exposure region. For the most frequently used radiographic conditions in Japan (120 kV, 2.5 mmAl, 200 cm SID, 10: 1 grid), the decrement in RMS granularity from 6 to 16 mAs was 0.0276 to 0.0253 (9.1%). This finding suggested that exposure exceeding 6 mAs did not improve image quality, i.e., exposure reduction down to 6 mAs would not cause a significant loss of image quality. It was therefore concluded that RMS granularity was a useful objective index by which to determine the upper limit of exposure. Use of the most frequent conditions with 6 mAs seemed to be recommendable as an initial condition for the technical optimization of CR chest radiography, since ESD under this condition was 0.265 mGy, which was approximately equal to the value of the ESD distribution of a total chest radiogram in Japan.     

Reduction in patient skin dose during interventional radiology with the use of an air gap substitute

Scattered radiation is inevitably generated in the patient couch during interventional radiology (IVR) procedures that use an under-couch tube system. Most of this scatter reaches the patient's skin surface and results in an increase in the skin dose without contributing to the diagnostic image. We considered that this unnecessary exposure could be reduced by the addition of an air gap between the couch and the patient. Because it is physically impossible to place an air gap on top of the couch and under the patient, we devised a new process in which an expanded polystyrene (EPS; rho = 0.0125 g cm(-3)) board is used as a substitute for the air gap. The results show that the EPS board played an effective role in reducing the skin dose to the patient. Using an EPS board 6 cm thick as an air gap substitute resulted in skin dose savings of approximately 9%. This method is easy to set up in clinical circumstances and is inexpensive. We recommend that this simple method of skin dose reduction be used for all IVR procedures.     

Dose and image quality in the comparison of analogue and digital techniques in paediatric urology examinations

In paediatric radiology it has been recognised that children have a higher risk of developing cancer from the irradiation than adults (two to three times); therefore, increased attention has been directed towards the dose to the patient. In this study the effect on patient dose and image quality in replacing the exposure in micturating cystourethrography (MCUG) examinations with the stored fluoroscopy image has been investigated. In the intravenous urography (IVU) examination we compared analogue and digital image quality, but the dose measurements were performed on a phantom. Standard clinical X-ray equipment was used. Sixty-eight patients in each of two centres were studied for the MCUG. Doses were measured with a dose-area product (DAP) meter and the image quality was scored. A non-parametric statistical analysis was performed. For the IVU, a phantom was used in the dose measurements but clinical images were scored in the comparison between analogue and digital images. For the MCUG, replacing the exposure with stored fluoroscopy images lowered the DAP value from 0.77 to 0.50 Gy cm². The image quality did not show any difference between the techniques; however, if reflux was to be graded, exposure was needed. For the IVU, the doses could be lowered by a factor of 3 using digital techniques. The image quality showed no statistical difference between the two techniques. There is a potential for a substantial dose reduction in both MUCG and IVU examinations using digital techniques.     

The radiation dose to the lens in radiology of the orbit

This paper describes research into measurement and reduction of the radiation dose to the lens during various examinations, namely skull and orbit, optic canal and optic strut, superior and inferior orbital fissure, localisation of foreign bodies in the eye, calcifications, orbital fractures, macrodacryography and orbital venography. Using rare-earth screens and high-sensitivity films, without an antiscattering grid, and with an added filtration of 0.5 mm Cu, it is possible to reduce the radiological risk during all investigations involving skull, orbit and eyeballs, while maintaining a good image quality. Particularly in those examinations with direct magnification (macrodacryography and venography, foreign bodies in the eye, orbital fractures), the dose to the lens is very low: less than 0.2 mGy/radiograph.     

Radiation dose in abdominal computed tomography: the role of patient size and the selection of tube current.

OBJECTIVE: To develop an algorithm for selecting tube current for computed tomography (CT), based on patient weight, that produces abdominal CT images of consistent image quality. METHODS: We recorded body weight and radiation exposure parameters for 37 patients undergoing abdominal CT. Two radiologists blind to the CT technique independently graded 11 measures of image quality, using a 5-point (5 = excellent, 4 = good, 3 = acceptable, 2 = poor, and 1 = unacceptable) scale. These scores were averaged to generate an overall image quality score. Using linear regression, we found a target image noise level that corresponded to an overall image quality score of 4.5. We measured CT image noise in 9 uniformly attenuating regions of interest in the liver and abdominal aorta. We used linear regression to assess the relation between tube current and image noise. A prediction equation was developed to set the tube current in different-sized patients to produce images at the target noise level. Finally, we calculated the dose savings that would have resulted with this tube-current selection technique. RESULTS: Image noise was correlated with patient weight (r2 = 0.81). At an overall image quality score of 4.5, the noise was 16 HU. Using this target noise value, we determined the required tube current for each patient weight and found that the use of this technique would have reduced radiation exposure for all patients weighing less than 70 kg. The dose reduction for the smallest patient (35.4 kg) was 72%. CONCLUSION: To produce CT scans of similar quality, a simple prediction equation can be developed for any scanner to optimize radiation dose for patients of all body weights.     

Chest radiography with a flat-panel detector: image quality with dose reduction after copper filtration

PURPOSE: To compare image quality and estimated dose for chest radiographs obtained by using a cesium iodide-amorphous silicon flat-panel detector at fixed tube voltage and detector entrance dose with and without additional 0.3-mm copper filtration. MATERIALS AND METHODS: The study was approved by the institutional ethics committee. All prospectively enrolled patients signed the written consent form. Chest radiographs in two projections were acquired at 125-kVp tube voltage and 2.5-microGy detector entrance dose. The experimental group (38 patients) was imaged with 0.3-mm copper filtration; the control group (38 patients) was imaged without copper filtration. An additional 12 patients were imaged with and without copper filtration and served as paired subject-controls. Three readers blinded to group and clinical data independently evaluated the radiographs for image quality on a digital display system. Twelve variables (six for each radiographic projection) were assigned scores on a seven-point ordinal scale. Scores between experimental and control groups were compared: Logistic regression analysis and Mann-Whitney U test were used for unpaired patients; and Wilcoxon and McNemar test, for paired patients. In all, 72 comparisons were determined (36 [12 variables x three readers] for unpaired patients and 36 for paired patients). In a phantom study, radiation burden of experimental protocol was compared with that of control protocol by using Monte Carlo calculations. RESULTS: For 70 of 72 comparisons, digital radiographs obtained with copper filtration were of similar image quality as radiographs obtained without copper filtration (P = .123 to P > .99). For two of 72 comparisons, one observer judged the experimental protocol superior to the control protocol (P = .043, P = .046). Patient dose reduction estimated with Monte Carlo calculations was 31%. Use of copper filtration increased exposure times by 48% for posteroanterior views and by 34% for lateral views. CONCLUSION: Subjectively equivalent chest radiographic image quality was found with estimated 30% dose reduction after addition of 0.3-mm copper filtration with flat-panel cesium iodide-amorphous silicon technology.