Affect Patient Dose Research Articles

Patient radiation dose during angiography and embolization for abdominal hemorrhage: the influence of CT angiography, fluoroscopy system, patient and procedural variables

BackgroundAngiography and embolization (AE) is a lifesaving, high radiation dose procedure for treatment of abdominal arterial hemorrhage (AAH). Interventional radiologists have utilized pre-procedure CT angiography (CTA) and newer fluoroscopic systems in an attempt to reduce radiation dose and procedure time.PurposeTo study the factors contributing to the radiation dose of AE for AAH and to compare to the reference standard.Materials and methodsThis retrospective single-centre observational cohort study identified 154 consecutive AE procedures in 138 patients (median age 65 years; interquartile range 54–77; 103 men) performed with a C-arm fluoroscopic system (Axiom Artis DTA or Axiom Artis Q (Siemens Healthineers)), between January 2010 and December 2017. Parameters analysed included: demographics, fluoroscopy system, bleeding location, body mass index (BMI), preprocedural CT, air kerma-area product (PKA), reference air kerma (Ka,r), fluoroscopy time (FT) and the number of digital subtraction angiography (DSA) runs. Factors affecting dose were assessed using Mann–Whitney U, Kruskal–Wallis one-way ANOVA and linear regression.ResultsPatients treated with the new angiographic system (NS) had a median PKA, median Ka,r, Q3 PKA and Q3 Ka,r that were 74% (p < 0.0005), 66%(p < 0.0005), 55% and 52% lower respectively than those treated with the old system (OS). This dose reduction was consistent for each bleeding location (upper GI, Lower GI and extraluminal). There was no difference in PKA (p = 0.452), Ka,r (p = 0.974) or FT (p = 0.179), between those who did (n = 137) or did not (n = 17) undergo pre-procedure CTA. Other factors significantly influencing radiation dose were: patient BMI and number of DSA runs. A multivariate model containing these variables accounts for 15.2% of the variance in Ka,r (p < 0.005) and 45.9% of the variance of PKA (p < 0.005).ConclusionRadiation dose for AE in AAH is significantly reduced by new fluoroscopic technology. Higher patient body mass index is an independent key parameter affecting patient dose. Radiation dose was not influenced by haemorrhage site or performance of pre-procedure CTA.

Assessment of the professional practice knowledge of computed tomography preceptors

ObjectivesThis study aimed to assess the knowledge and practice of computed tomography (CT) clinical practice preceptors in terms of CT parameters affecting patient dose and image quality. Material and methodsA self-administered questionnaire that surveyed the participants’ demographic information and knowledge about CT parameters and radiation doses was distributed to 60 CT preceptors. ResultsThe response rate of the invited technologists was 92 %. 38 (69 %) males and 17 (31 %) females aged between 24 and 59 years, with a mean age of 37.8. The participants’ experience ranged between 2 and 24 years, with a mean of 15.5 years. The average knowledge score was 72.2 %, with a range of correct answers of 9–18 and a mean (±SD) of 13.1 ± 2.1. The participants showed a low awareness of diagnostic reference levels (DRLs). However, they demonstrated good overall knowledge, with a potential for improvement and confidence in practice. ConclusionsContinuous medical education and professional development are a priority for improvement to ensure reliable delivery of health care and best practice. The findings of this study can be used by education institutes and health organizations when designing educational programs to ensure the highest training and performance of their technologists.

Advancing Safety: Role of Equipment Design and Configuration Change in Pediatric Fluoroscopy.

Diagnostic x-ray exams irradiate the patient to produce an x-ray pattern in space, which is captured and processed into a visible image, followed by clinical interpretation. Diagnostic-quality images at a well-managed radiation dose are required. Improvements to image receptors and image processing algorithms have resulted in improved images at reduced dose levels. However, careful management of x-ray production via design or configuration changes of the imaging device also affect patient dose. This initial dose management step is the focus of this discussion. Imaging equipment vendors, in general, have produced quality images of adults at reasonably managed patient doses. This achievement required teamwork between leading adult hospital staff members and representatives of the imaging equipment vendor within the adult hospital. Most manufacturers have had less opportunity to develop similar optimized configurations for pediatric imaging, the imaging of patients ranging from 2-200 kg between 0-21 y of age. Challenges: The wider dynamic range of patient thicknesses in the pediatric size range compared to the adult range of only 45-140 kg challenges automatic control features. In recent years reduction of patient dose as opposed to proper management has been stressed. The principal objectives of end users and vendors, respectively, are patient care and the bottom line. This too often hampers (if not prevents) a productive working relationship between the vendor and the end user. Too many end users rely too heavily on their equipment vendor to solve imaging/dose concerns. The vendors have an important role to play in this challenge but should not be the sole solution. Qualified medical physicists need an understanding of the design of the imaging device, an understanding that many vendors do not support out of proprietary concerns. The performance of the equipment should be judged based on data acquired with better tools. Solutions: Multiple equipment configurations are needed-each designed to excel at a reduced size of patients. Dose reductions that significantly impact image quality must be rejected. Radiologists and their qualified medical physicists should develop target patient doses (size based) for their unique imaging equipment and preferred level of quantum mottle. Once target doses are established as a function of patient size, vendor application specialists and design engineers should leverage the equipment's strengths and weaknesses to best achieve desired results. The qualified medical physicist should function as an interpreter between the end user and the vendor's design engineers. Are the radiologists' and technologists' expectations of the vendor reasonable and vice versa? While better tools are being developed, vendors may hesitate to make them available or charge excessive dollars for these new features to further slow their adoption. Conclusion: The challenges and solutions require the radiologist, technologist, qualified medical physicist, and vendor representatives to work as a team to manage patient dose and maintain image quality. The installed imaging device will be only as successful as the working relationship between the parties. These challenges and conflicts must continually be overcome to provide the best patient care.

Dose reference levels and clinical determinants in stroke neuroradiology interventions.

To establish dose reference levels (RLs) for stroke interventions while carefully analysing the impact of clinical and technical parameters on patient exposure. The study retrospectively analysed data from 377 stroke patients prospectively collected between 15 October 2015 and 30 March 2017 at a single, level-3 stroke centre equipped with Philips Allura Clarity systems. Local dose RLs were first derived as the 75th percentile of the dose area product (DAP), cumulative air kerma (Ka,r), fluoroscopy time (FT) and the number of images (NI). Univariate and multivariate negative binomial regressions were considered for the statistical analysis to investigate the dose variability with clinical and technical parameters such as patient's age and sex, occlusion removal technique, number of passages, single-plane or biplane equipment, etc. RESULTS: Local stroke dose RLs were derived in terms of total DAP (162 Gy cm2), Ka,r (854 mGy), FT (42 min) and NI (559). Gender (relative dose multiplier (RDM) 1.31; 95% CI 1.12-1.45), number of passages (RDM 1.22 per passage; 95% CI 1.10-1.22) and procedure success (RDM 0.52, 95% CI 0.55-0.80) proved to be key parameters affecting patient dose. Meanwhile the statistical analysis did not find any difference in relative dose received by patients owing to age, baseline NIHSS score, occlusion removal technique, posterior circulation, support of an anaesthesiologist or use of biplane equipment. Stroke dose RLs introduced in this work promote the optimisation of patient doses. Male gender, number of passages and success of recanalisation are independent key parameters affecting patient dose. • Stroke dose RLs derived in terms of total DAP (162 Gy cm 2 ), K a,r (854 mGy), FT (42 min) and NI (559) will help optimise the radiation safety of patients treated with mechanical thrombectomy. • Male gender (relative dose multiplier 1.31; 95% CI 1.12-1.45), number of passages (RDM 1.22 per passage; 95% CI 1.10-1.22) and success of recanalisation TICI score > 2b (RDM 0.52, 95% CI 0.55-0.80) are independent key parameters affecting patient dose. • Stent retriever or aspiration technique showed no significant difference in terms of the dose delivered to the patient; neither technique should be favoured for dosimetric reasons provided that there is no difference regarding clinical outcomes.

Retrieval, visualization, and mining of large radiation dosage data

Radiation dose monitoring has become an essential service that hospitals must perform. Depending on the system in place, this can result in the collection of large quantities of data, ripe for analysis. These data should include a wide variety of variables for each study because assessment of the propriety of the patient's dose is dependent on many factors, including patient age and size, as well as the body section that is being scanned. Moreover, the scanners themselves have many properties that affect patient dose, such as model, pitch and kVp. In this paper, we propose an engine that seamlessly integrated with a clinical PACS to retrieve radiation dosage data. We devised several schemes to analyze these data through visualization and mining techniques that examine it at different scopes. We demonstrate the utility of such visual methods at examining large, noisy, and multi-dimensional data, which is embodied in the collected radiation data.

An Analysis of 3 Common CardioGen-82 82Rb Infusion System Injection Methods and Their Impact on Clinical Volume and Image Counts.

In the wake of the Food and Drug Administration (FDA) recall, many clinics have had to reduce their examination volumes to meet the new generator volume usage requirements. This review tests 3 common infusion methods and how they affect patient dose, generator volume usage, image counts, and generator volume limits. Three common configurations of the (82)Rb infusion system settings--standard 50-mL, volume-limiting, and bolus methods--were tested to determine how they affect patient dose, generator volume, and image counts. Each injection configuration was tested daily for the duration of 3 consecutive generators by injection into separate vials. Each injection configuration was also infused into a beaker and imaged to determine the impact of image counts for each method. The total estimated volumes for multiple examination and quality assurance clinical situations were simulated to observe the use of each method relative to the new FDA volume alert and expiration limits. Vial tests confirmed that the bolus method used the least amount of volume per infusion and stayed the most consistent throughout the life of the generator. The bolus method also produced a lower patient dose after approximately 10 d of use. The beaker tests in the scanner showed that the standard 50-mL method produced the greatest number of total counts for the flow and uptake images. On the basis of the estimated total volume simulations, the bolus method allowed for the most examinations over the life of the generator while staying within the new FDA limits. All 3 methods for augmenting the (82)Rb infusion system produced different outcomes for patient dose, image counts, and total generator volume use. The standard 50-mL method ensured the maximum amount of counts available for imaging throughout the life of the generator. The bolus method provided a consistent and predictable amount of volume use. The volume-limiting method fell somewhere in the middle of volume predictability and count preservation.

Investigation of the influence of image reconstruction filter and scan parameters on operation of automatic tube current modulation systems for different CT scanners.

Variation in the user selected CT scanning parameters under automatic tube current modulation (ATCM) between hospitals has a substantial influence on the radiation doses and image quality for patients. The aim of this study was to investigate the effect of changing image reconstruction filter and scan parameter settings on tube current, dose and image quality for various CT scanners operating under ATCM. The scan parameters varied were pitch factor, rotation time, collimator configuration, kVp, image thickness and image filter convolution (FC) used for reconstruction. The Toshiba scanner varies the tube current to achieve a set target noise. Changes in the FC setting and image thickness for the first reconstruction were the major factors affecting patient dose. A two-step change in FC from smoother to sharper filters doubles the dose, but is counterbalanced by an improvement in spatial resolution. In contrast, Philips and Siemens scanners maintained tube current values similar to those for a reference image and patient, and the tube current only varied slightly for changes in individual CT scan parameters. The selection of a sharp filter increased the image noise, while use of iDose iterative reconstruction reduced the noise. Since the principles used by CT manufacturers for ATCM vary, it is important that parameters which affect patient dose and image quality for each scanner are made clear to operator to aid in optimisation.

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

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

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

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

Poster — Thur Eve — 51: An Investigation of Geometry Issues for EPID Dosimetry during Rotational IMRT

INTRODUCTION: Amorphous‐silicon electronic portal imaging devices (EPIDs) have been established as useful tools for dosimetry. To accurately reconstruct the patient dose delivered during rotational IMRT, one must acquire time‐resolved EPID images as a function of gantry‐angle. Dose reconstruction accuracy is directly impacted by the accuracy of the geometry of the imaging system, including the gantry‐angle readout (i.e. source geometry) and the EPID support‐arm sag (i.e. imager geometry). This work investigates these two factors. METHODS: The EPID support‐arm sag was investigated through measurements performed on Varian E‐arm and R‐arm models at two institutes and employing two different analysis methods. One method imaged an isocentric ball‐bearing whose position was tracked over all gantry‐angles. The second method involved analysing field edges to obtain the field centre location of all images. Gantry‐angle accuracy was examined by comparing the gantry‐angle indicated at the treatment console readout to the gantry‐angle written to the EPID DICOM header. We developed a method of measuring gantry‐angle directly from the gantry‐angle potentiometer. RESULTS: The E‐arm showed maximum displacement of roughly 0.6mm (cross‐plane) and 0.8mm (in‐plane). R‐arm results were significantly worse, estimated at 8.5mm (cross‐plane) and 5.0mm (in‐plane). Gantry‐angle analysis demonstrated approximately 2 degrees of uncertainty in the gantry‐angle contained in the EPID image. A direct measurement of the gantry angle potentiometer was demonstrated. CONCLUSIONS: Two main factors affecting patient dose reconstruction using EPID dosimetry have been investigated. EPID support‐arm sag can be measured (and corrected). Near real‐time gantry‐angle measurement can be performed through directly monitoring the potentiometer signal.

WE‐A‐210A‐01: Fluoroscopic Imaging Equipment: Guidelines for Detector Input Dose Settings and Image Optimization

Modern fluoroscopy imaging equipment is designed to simultaneously monitor x‐ray generator parameters, detector exposure rate, contrast‐to‐noise ratio, and x‐ray tube loading. Under programmed control, fluoroscopy systems automatically make adjustments to the parameters controlling x‐ray production, beam filtration, detector signal output, digital image processing, and image presentation. Any means intended to reduce patient dose should be implemented in a way that preserves image quality.For the clinical medical physicist, optimization of fluoroscopic equipment performance begins with an understanding of the variable system parameters, and the identification of the trigger points for changes in these parameters. Secondly, an understanding of how system parameters affect each other, affect image quality, and affect patient dose can lead to better choices in how the system should be set up for specific applications.A necessary requirement is an understanding of what detector input dose one should expect with an image intensifier fluoroscopy system, and how the detector dose should change when a flat panel detector is utilized. It is also necessary to understand how operational settings on the equipment can obviate superior detector performance as determined by detector type and metrics. This presentation will use imaging examples from installed systems to explore these issues. Also, a clear, concise guideline for determining the appropriate fluoroscopy detector input dose rate for both image intensifier and flat panel detectors will be presented.Learning Objectives:1. Provide an understanding of modern fluoroscopic imaging system component design and functionality2. Determine the appropriate fluoroscopy detector input dose rate for image intensifier and flat panel detectors3. Describe specific ways in which equipment settings can enhance or detract from optimum performance.

Poster - Thurs Eve-32: Dose errors related to the treatment couch.

Modern radiotherapy linacs often use carbon fibre for their couch tops due to its radio translucent properties. Beam attenuation by the couches is often ignored during planning and MU calculation. This work examines beam attenuation and loss of "skin sparing" (dose build up region) when various photon beams transit either the MedTec (Siemens) or Medical Intelligence (Elekta) couches. Additionally, measured doses were compared to CMS treatment planning system (XiO version 4.33.02) predictions. We found the two couches to have different structures, resulting in different attenuation signatures as a function of gantry angle. For normal beam incidence the Siemens and Elekta couches had radiological thicknesses of 4.5 mm and 6.0 mm, respectively. For a normal incidence 10×10 cm2 6MV beam the surface dose after couch transmission was 93% vs. 83% for Elekta and Siemens, respectively. Conversely, the increased mass on the lateral edge of the Siemens couch resulted in a maximum attenuation (6 MV 5×5 cm2 beams) of 8% compared to 5% by the Elekta couch. Incorporating the treatment couch as part of the patient planning CT allowed the CMS TPS model to calculate couch attenuation within 1% of measurement, except at the very edge of the Siemens couch, where the attenuation is strongly gantry angle dependent. The CMS beam model was also able to predict the loss of skin sparing within 1%. In conclusion, the two patient couches are different, but both can significantly affect patient dose which can be accounted for in the CMS TPS.

MO‐A‐352‐01: Fluoroscopic Imaging Equipment

Modern fluoroscopy imaging equipment is designed to simultaneously monitor x‐ray beam attenuation, detector exposure rate, contrast‐to‐noise ratio, x‐ray generator parameters, and x‐ray tube loading. Knowledge of system design is essential to understanding equipment operation; and understanding equipment operation can facilitate optimization of performance. Under pre‐programmed control, fluoroscopy systems automatically make adjustments to the parameters controlling x‐ray production, beam filtration, detector signal output, digital image processing, and image presentation. The result is that reduction of patient dose does not necessarily require a loss of image quality.Optimizing performance begins with the determination of which system parameters are dynamically controlled, and the identification of the trigger points for changes in these parameters. Secondly, an understanding of how system parameters affect each other, affect image quality, and affect patient dose can lead to better choices in how the system should be set up for specific applications. This presentation will systematically describe the functions of the major system components including automatic exposure rate control, variable pulse‐rate fluoroscopy, generator operating curves, spectral beam filtration, and other factors that affect the ability of the imaging system to deliver optimum diagnostic images at moderate patient dose.Educational Objectives:1. Provide an understanding of modern fluoroscopic imaging system component design and functionality.2. Describe specific ways in which equipment settings can enhance or detract from optimum performance.

Radiation Dose-Reduction Strategies for Neuroradiology CT Protocols

Within the past 2 decades, the number of CT examinations performed has increased almost 10-fold. This is in large part due to advances in multidetector-row CT technology, which now allows faster image acquisition and improved isotropic imaging. The increased use, along with multidetector technique, has led to a significantly increased radiation dose to the patient from CT studies. This places increased responsibility on the radiologist to ensure that CT examinations are indicated and that the "as low as reasonably achievable" concept is adhered to. Neuroradiologists are familiar with factors that affect patient dose such as pitch, milliamperes, kilovolt peak (kVp), collimation, but with increasing attention being given to dose reduction, they are looking for additional ways to further reduce the radiation associated with their CT protocols. In response to increasing concern, CT manufacturers have developed dose-reduction tools, such as dose modulation, in which the tube current is adjusted along with the CT acquisition, according to patient's attenuation. This review will describe the available techniques for reducing dose associated with neuroradiologic CT imaging protocols.

MO-B-330A-01: Patient Radiation Doses in Diagnostic Imaging

The main goal of this presentation is to discuss factors which affect patient radiationdose delivered during various diagnostic radiology imaging examinations and to relate these radiationdoses to potential biological risks. Measurement methods to estimate patient radiationdoses and some examples of dose reduction for radiography,mammography,fluoroscopy,angiography and CT will be reviewed. Applications of these measurements to patient dose estimation will be shown. Procedures to obtain quick computational estimates of patient doses for IRB submissions, patient inquiries and fetal dose estimations will be provided. Approaches to convert entrance skindoses,dose area products and dose length products to effective doses and risks will be discussed. Typical patient radiationdose values for common diagnosticimaging procedures will be given. Limitations, uncertainties and ranges for patient radiationdose estimates will be examined. The utilization of “reference values” for patient radiationdoses will be reviewed. Some guidelines to aid physicists with relating radiationdose issues to the public and informational media will also be included. The material is intended to provide a brief overview of one crucial aspect of the responsibilities with which diagnosticmedical physicists and medical health physicists must routinely handle in their jobs. Our expectation is to stimulate introspective assessments and to expand the manner in which patient radiationdose determinations are viewed and performed. Educational Objectives: 1. To review fundamental X‐ray dosimetry quantities. 2. To identify important factors that affect patient dose delivered by various X‐ray imaging modalities. 3. To describe common methods to measure patient dose and review strategies in developing patient dose charts for routine diagnosticimaging procedures. 4. To examine the limitations of some current dosimetry methodologies. 5. To present a practical guidance to physicists in providing day‐to‐day clinical support service such as IRB submissions, patient inquiries and fetal dose estimations.

Source to image receptor distance

CorrespondenceSource to image receptor distanceP C Brennan and D O'learyP C BrennanSchool of Medicine and Medical Sciences, University College Dublin, Belfield, Dublin 4, IrelandSearch for more papers by this author and D O'learySchool of Medicine and Medical Sciences, University College Dublin, Belfield, Dublin 4, IrelandSearch for more papers by this authorPublished Online:5 Mar 2014https://doi.org/10.1259/bjr/60546865SectionsPDF/EPUBFull Text ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail About"Source to image receptor distance." The British Journal of Radiology, 79(939), p. 266 References 1 Poletti JL, McLean D. The effect of source to image-receptor distance on effective dose for some common X-ray projections. Br J Radiol 2005;78:810–5. Link ISI, Google Scholar2 O'Leary D, McDonnell S, Brennan PC. Increasing film focus distance (FFD) reduces radiation dose for X-ray examinations. Radiat Prot Dosim 2004;108:263–8. Crossref Medline ISI, Google Scholar Previous article Next article FiguresReferencesRelatedDetailsCited byA comparison of effective dose and risk for different collimation options used in AP shoulder radiographyRadiography, Vol. 265Does collimation affect patient dose in antero-posterior thoraco-lumbar spine?Radiography, Vol. 23, No. 3 Volume 79, Issue 939March 2006Pages: 183-270 © The British Institute of Radiology History Published onlineMarch 05,2014 Metrics Download PDF

Dose and image quality. How does the choice of kilovoltage affect patient dose, scattered radiation, and image quality in CT examinations? Submitted by Glen Thomson, Middlemore Hospital, New Zealand.

Published online: 5 December 2003 Springer-Verlag 2003 How does the choice of KV affect patient dose, scattered radiation, and image quality in CT examinations? When the x-ray tube voltage (kV) in CT is reduced while keeping the mAs constant, the patient dose is decreased. Dropping the x-ray tube voltage from 120 to 80 kV at a constant current (mAs) typically reduces the patient dose by about 60% because of the large reduction in x-ray tube output. The choice of kV dose not affect the amount of ‘‘scatter’’—CT has negligible image scatter since the thin detector (up to 2–3 cm) and the data acquisition geometry ensure that most scattered photons miss the detector. The contrast of a lesion relative to the surrounding background generally increases as kV is reduced, but the noise (mottle) level also increases since there are fewer photons at the lower kV (hence the lower patient dose). The lesion contrast-tonoise ratio (CNR) generally gets worse as the kV is reduced at a constant mAs in CT—the increase in contrast is less than the corresponding increase in noise [1]. If one reduces the kV and increases the mAs, however, it may be possible to maintain image quality (CNR) while reducing patient doses. CT optimization with respect to x-ray tube voltage is being investigated by several researchers, with initial findings suggesting that the use of lower kV values is promising for CT performed using iodinated contrast material [2, 3]. To summarize, reducing the CT kV at a constant mAs will always reduce the patient dose, and would probably reduce the lesion CNR. When iodine is administered to a patient, reducing the kV is likely to reduce patient doses with no adverse effect on CNR.

Factors influencing fluoroscopy time and dose-area product values during ad hoc one-vessel percutaneous coronary angioplasty.

X-ray exposure during radiologically guided interventional procedures may have some deleterious effects. The aim of our study was to analyse the factors affecting patient dose during percutaneous coronary angioplasty (PTCA). We evaluated radiation dose during coronary angiography followed by one-vessel PTCA in 402 consecutive patients who were treated by three experienced physicians using both femoral and radial techniques. Fluoroscopy time (t) and patient dose measured by a dose-area product (DAP) meter were recorded. A good correlation was observed between t and the DAP (r=0.78, p<0.001). To assess the factors affecting radiation exposure, we studied the differences between operators, arterial catheterization access and stenting strategy. Median (25th to 75th percentiles) values for t were 19 (13 to 26) min and for DAP were 191 (145 to 256) Gy cm(2) for operator 3 compared with t=12 (9 to 18) min and DAP=137 (91 to 208) Gy cm(2) for operator 2 (p<0.005 versus operator 3) and t=13 (9 to 17) min, and DAP=134 (93 to 190) Gy cm(2) for operator 1 (p<0.001 versus operator 3). Differences between the radial and the femoral techniques were: t=17 (13 to 24) min versus 12 (8 to 17) min, (p<0.001) and DAP=175 (128 to 246) Gy cm(2) versus 138 (93 to 197) Gy cm(2), (p<0.001). In comparison with stenting without pre-dilation, direct stenting significantly reduced t and DAP [t=12 (9 to 16) min versus 16 (11 to 22) min, (p<0.001) and DAP=130 (95 to 186) Gy cm(2) versus 163 (119 to 230) Gy cm(2), respectively, (p<0.01)]. Radiation exposure to patients and staff are strongly dependent on operators, stenting strategy and the arterial access chosen for ad hoc one-vessel PTCA.

Radiation exposure and image quality in chest CT examinations.

The purpose of this study was to determine how changes in radiographic tube current affect patient dose and image quality in unenhanced chest CT examinations. Ten sets of CT images were obtained from patients undergoing CT-guided chest biopsies. For each patient, six images of the same region were obtained at settings between 40 and 280 mAs. CT data were used to reconstruct tomographic sections with a field of view limited to the normal contralateral lung. Images were printed using lung and mediastinal image display settings. Image quality was determined by asking radiologists to assess the perceived level of mottle in CT images. Five chest radiologists ranked the relative image quality of six images. Patient effective doses were computed for chest CT examinations performed at each milliampere-second setting. Radiologists indicated whether any perceived improvement of image quality at the higher radiation exposures was worth the additional radiation dose. The differences in quality of chest CT images generated at greater than or equal to 160 mAs were negligible. Reducing the radiographic technique factor below 160 mAs resulted in a perceptible reduction in image quality. Differences in CT image quality for radiographic techniques between 120 and 280 mAs were deemed to be insufficient to justify any additional patient exposure. However, the use of 40 mAs results in an inferior image quality that would justify increased patient exposure. Radiographic techniques for unenhanced chest CT examinations can be reduced from 280 to 120 mAs without compromising image quality.

01-4 How does the X-ray tube potential affect patient dose and image quality in abdominal CT?

01-4 How does the X-ray tube potential affect patient dose and image quality in abdominal CT?