Effect of multislice scanners on patient dose from routine CT examinations in East Anglia

Evaluation of Radiation Doses from Computed Tomography Conducted in Al Jouf Region (Saudi Arabia)

A safe radiation dose from computed tomography (CT) is normally specified through the Computed Tomography Dose Index (CTDI) as an “effective dose.” Radiation exposure from CT is relatively high in comparison with other radiological tests. In this paper, we evaluate doses used on adult patients during typical CT scans, in Al Jouf, the northern region of Saudi Arabia. Scanning processes were taken place in different parts of the body; including the pelvis, head, abdomen, and chest. The dose indices were calculated using the CT-expo v2.5 computer software. A comparison of the results with similar investigations, regionally and globally, was made. Other comparisons between displayed and calculated dose indices were also performed. The main values of CT volume are the dose index (CTDIvol) and dose-length product (DLP). The effectiveness results for head CTs were 45.0 mGy, 488 mGy.cm, and 5.2 mSv; while for pelvic CTs they were 16.4 mGy, 391 mGy.cm, and 4.0 mSv; whereas for abdominal CTs they were 22.2 mGy, 613 mGy.cm, and 6.5 mSv; finally they were 17.5 mGy, 380 mGy.cm, and 3.9 mSv for chest CTs. It is confirmed that the values obtained are within the internationally accepted values, except for the values of the head examination, in which the effective dose value of 5.2 mSv was higher than the recommended value. This work gives an overview of the doses received by adult patients during regular CT examination. It is the first regional CT dose survey and provides a baseline for improvement and quality control in the region of Al Jouf.

Knowledge and Associated Factors of Medical Students Regarding Radiation Exposure from Common Diagnostic Imaging Procedures at the University of Gondar, Ethiopia

Background

Physicians’ knowledge about radiation exposure and risks was previously reported as inadequate. Therefore, the aim of this study was to assess knowledge and associated factors regarding radiation exposure among medical students from common diagnostic imaging procedures at the University of Gondar.

Methods

A cross-sectional study was conducted to assess knowledge and associated factors regarding radiation exposure among medical students. A total of 473 medical students (first through sixth years of study) completed a structured questionnaire. Univariate and multi-variable binary logistic regression was used to see the factors associated with knowledge of medical students on radiation sources, exposure and risks. Variables with p-value <0.2 during the bivariable binary logistic regression were tested in the multivariable binary logistic regression. P-value<0.05 was used to declare significant association at the final model.

Result

Response rate was 100%. Two hundred fifteen (45.5% 95% confidence interval (CI )(41.0%–50.3%)) participants had good knowledge regarding radiation exposure from diagnostic imaging procedures. Only 177(37.4%) participants correctly knew that Computer Tomography (CT) use X-ray. However, subjects incorrectly named magnetic resonance imaging (MRI) as if it used x-ray (12.1%) and source of ionizing radiation (19.5%). Being female [Adjusted-odds-ratio (AOR)=1.57,95% CI(1.05,2.36)], 18-20 years of age [AOR=2.18, 95% CI(1.26, 3.76)], and 1^st to 3^rd year of study [AOR=3.64, 95% CI(2.23,5.95)] were predictors of knowledge identified.

Conclusion

The results highlight that medical students need to be trained well with sufficient radiological education that enable them later to adhere to safe practices.

Effective and organ doses from common CT examinations in one general hospital in Tehran, Iran

Purpose: It is well known that the main portion of artificial sources of ionizing radiation to human results from X-ray imaging techniques. However, reports carried out in various countries have indicated that most of their cumulative doses from artificial sources are due to CT examinations. Hence assessing doses resulted from CT examinations is highly recommended by national and international radiation protection agencies. The aim of this research has been to estimate the effective and organ doses in an average human according to 103 and 60 ICRP tissue weighting factor for six common protocols of Multi-Detector CT (MDCT) machine in a comprehensive training general hospital in Tehran/Iran.

Methods: To calculate the patients' effective dose, the CT-Expo2.2 software was used. Organs/tissues and effective doses were determined for about 20 patients (totally 122 patients) for every one of six typical CT protocols of the head, neck, chest, abdomen-pelvis, pelvis and spine exams. In addition, the CT dosimetry index (CTDI) was measured in the standard 16 and 32 cm phantoms by using a calibrated pencil ionization chamber for the six protocols and by taking the average value of CT scan parameters used in the hospital compared with the CTDI values displayed on the console device of the machine.

Results: The values of the effective dose based on the ICRP 103 tissue weighting factor were: 0.6, 2.0, 3.2, 4.2, 2.8, and 3.9 mSv and based on the ICRP 60 tissue weighting factor were: 0.9, 1.4, 3, 7.9, 4.8 and 5.1 mSv for the head, neck, chest, abdomen-pelvis, pelvis, spine CT exams respectively. Relative differences between those values were -22, 21, 23, -6, -31 and 16 percent for the head, neck, chest, abdomen-pelvis, pelvis, spine CT exams, respectively. The average value of CTDIv calculated for each protocol was: 27.32 ± 0.9, 18.08 ± 2.0, 7.36 ± 2.6, 8.84 ± 1.7, 9.13 ± 1.5, 10.42 ± 0.8 mGy for the head, neck, chest, abdomen-pelvis and spine CT exams, respectively.

Conclusions: The highest organ doses delivered by various CT exams were received by brain (15.5 mSv), thyroid (19.00 mSv), lungs (9.3 mSv) and bladder (9.9 mSv), bladder (10.4 mSv), stomach (10.9 mSv) in the head, neck, chest, and the abdomen-pelvis, pelvis, and spine respectively. Except the neck and spine CT exams showing a higher effective dose compared to that reported in Netherlands, other exams indicated lower values compared to those reported by any other country.

Single-energy pediatric chest computed tomography with spectral filtration at 100 kVp: effects on radiation parameters and image quality

BACKGROUND

Most of the applied radiation dose at CT is in the lower photon energy range, which is of limited diagnostic importance.

OBJECTIVE

To investigate image quality and effects on radiation parameters of 100-kVp spectral filtration single-energy chest CT using a tin-filter at third-generation dual-source CT in comparison to standard 100-kVp chest CT.

MATERIALS AND METHODS

Thirty-three children referred for a non-contrast chest CT performed on a third-generation dual-source CT scanner were examined at 100 kVp with a dedicated tin filter with a tube current-time product resulting in standard protocol dose. We compared resulting images with images from children examined using standard single-source chest CT at 100 kVp. We assessed objective and subjective image quality and compared radiation dose parameters.

RESULTS

Radiation dose was comparable for children 5 years old and younger, and it was moderately decreased for older children when using spectral filtration (P=0.006). Effective tube current increased significantly (P=0.0001) with spectral filtration, up to a factor of 10. Signal-to-noise ratio and image noise were similar for both examination techniques (P≥0.06). Subjective image quality showed no significant differences (P≥0.2).

CONCLUSION

Using 100-kVp spectral filtration chest CT in children by means of a tube-based tin-filter on a third-generation dual-source CT scanner increases effective tube current up to a factor of 10 to provide similar image quality at equivalent dose compared to standard single-source CT without spectral filtration.

National diagnostic reference level initiative for computed tomography examinations in Kenya

The purpose of this study was to estimate the computed tomography (CT) examination frequency, patient radiation exposure, effective doses and national diagnostic reference levels (NDRLs) associated with CT examinations in clinical practice. A structured questionnaire-type form was developed for recording examination frequency, scanning protocols and patient radiation exposure during CT procedures in fully equipped medical facilities across the country. The national annual number of CT examinations per 1000 people was estimated to be 3 procedures. The volume-weighted CT dose index, dose length product, effective dose and NDRLs were determined for 20 types of adult and paediatric CT examinations. Additionally, the CT annual collective effective dose and effective dose per capita were approximated. The radiation exposure during CT examinations was broadly distributed between the facilities that took part in the study. This calls for a need to develop and implement diagnostic reference levels as a standardisation and optimisation tool for the radiological protection of patients at all the CT facilities nationwide.

Computed tomography dose index for head CT in northern Nigeria

Computed tomography dose index w and dose length product were recorded for the purpose of developing diagnostic reference levels (DRLs) for radiation dose optimisation. The study was conducted in three radiology departments with CT centres in Northern Nigeria. Data were collected from 54 consenting adult participants (weighing 70 kg ± 3) that had head CT scans. Analysis was done using SPSS version statistical software. A combined dose for the three centres was calculated and compared with the reported data from the international communities where there are established DRLs. Third quartile values of CTDIw and DLP were determined as 77 mGy and 985 mGy cm, respectively. Local DRLs that are significantly higher than most of the reported data in the literature have been established.

Automated Tube Potential Selection as a Method of Dose Reduction for CT of the Neck: First Clinical Results

OBJECTIVE

The objective of our study was to investigate whether the use of a software-based automated tube potential selection (ATPS) CT neck protocol can result in radiation dose reduction as compared with a set 120-kV protocol without a statistically significant reduction in image quality.

MATERIALS AND METHODS

Three hundred sixty-four patients (median age, 52 years) underwent CT of the neck. Group 1 (n = 320) underwent CT with ATPS with 80, 100, or 120 kV. Group 2 (n = 44) was examined with the standard CT protocol at 120 kV. Attenuation, image background noise, signal-to-noise ratio (SNR), dose-length product (DLP), volume CT dose index (CTDIvol), body mass index (BMI [weight in kilograms divided by the square of height in meters]), and subjective image quality (5-point Likert scale, two readers in consensus) were analyzed.

RESULTS

A tube potential of 100 kV was selected in 279 patients, 120 kV in 40 patients, and 80 kV in one patient of the ATPS group. A significant correlation was found for selected tube potential and BMI (80 kV, BMI = 20.4; 100 kV, mean BMI = 24.2; 120 kV, BMI = 28.6; r = 0.28, p < 0.01). The average radiation dose was significantly lower with ATPS activated than with the standard protocol (mean DLP, 259 vs 350 mGy × cm, respectively). Background noise did not differ between groups 1 and 2 at the levels of the mandibular angle and the upper mediastinum; however, attenuation and SNR increased significantly with lower tube potential settings. Subjective image quality did not suffer (mean image quality score: ATPS protocol vs standard protocol, 4.56 vs 4.61, respectively; p > 0.05) with good interobserver agreement (κ > 0.56).

CONCLUSION

ATPS allows significant dose savings for CT of the neck compared with a standard protocol that uses a fixed 120-kV setting without a statistically significant reduction in image quality.

Patient dose for computed tomography examination: dose reference levels and effective doses based on a national survey of 2013 in Korea

14,620 sets of patient dose data were obtained for 31 different models of computed tomography (CT) equipment (total 73) with 18 types of CT examination in Korea. Specific diagnostic reference levels (DRLs) for this study in terms of third quartile volumetric CT dose index in mGy [and dose-length product (DLP) in mGy.cm] are as follows: head, 53 (910); neck, 20 (770); chest, 14 (710); abdomen, 14 (1000); stomach, 14 (1000); liver, 14 (1700); pancreas, 14 (1700); kidney, 14 (2100); cervical spine, 30 (600); lumbar spine, 25 (760); hip, 17 (600); cardiac CT angiography, 45 (1250); head CT angiography, 43 (1900); liver CT angiography, 14 (1400) and thoraco-abdominal CT angiography, 16 (2000). In the present study, DRLs in terms of volumetric CT dose index were below previously published reference levels, partly because the newer CT equipments have improved technology that facilitates lower patient dose. Meanwhile, DRLs in terms of DLP were higher, because multi-phase scanning protocols with prolonged scan coverage have been widely used.

Acute intracranial hemorrhage in CT: benefits of sinogram-affirmed iterative reconstruction techniques

BACKGROUND AND PURPOSE

Acute intracranial hemorrhage represents a severe and time critical pathology that requires precise and quick diagnosis, mainly by performing a CT scan. The purpose of this study was to compare image quality and intracranial hemorrhage conspicuity in brain CT with sinogram-affirmed iterative reconstruction and filtered back-projection reconstruction techniques at standard (340 mAs) and low-dose tube current levels (260 mAs).

MATERIALS AND METHODS

A total of 94 consecutive patients with intracranial hemorrhage received CT scans either with standard or low-dose protocol by random assignment. Group 1 (n=54; mean age, 64 ± 20 years) received CT at 340 mAs, and group 2 (n=40; mean age, 57 ± 23 years) received CT at 260 mAs. Images of both groups were reconstructed with filtered back-projection reconstruction and 5 iterative strengths (S1-S5) and ranked blind by 2 radiologists for image quality and intracranial hemorrhage on a 5-point scale. Image noise, SNR, dose-length product (mGycm), and mean effective dose (mSv) were calculated.

RESULTS

In both groups, image quality and intracranial hemorrhage conspicuity were rated subjectively with an excellent/good image quality. A higher strength of sinogram-affirmed iterative reconstruction showed an increase in image quality with a difference to filtered back-projection reconstruction (P < .05). Subjective rating showed the best score of image quality and intracranial hemorrhage conspicuity achieved through S3/S4-5. Objective analysis of image quality showed in an increase of SNR with a higher strength of sinogram-affirmed iterative reconstruction. Patients in group 2 (mean: 744 mGycm/1.71 mSv) were exposed to a significantly lower dose than those in group 1 (mean: 1045 mGycm/2.40 mSv, P < .01).

CONCLUSIONS

S3 provides better image quality and visualization of intracranial hemorrhage in brain CT at 260 mAs. Dose reduction by almost one-third is possible without significant loss in diagnostic quality.

[State of the art and future trends in technology for computed tomography dose reduction]

The introduction of helical and multislice acquisitions in CT scanners together with decreased image reconstruction times has had a tremendous impact on radiological practice. Technological developments in the last 10 to 12 years have enabled very high quality images to be obtained in a very short time. Improved image quality has led to an increase in the number of indications for CT. In parallel to this development, radiation exposure in patients has increased considerably. Concern about the potential health risks posed by CT imaging, reflected in diverse initiatives and actions by official organs and scientific societies, has prompted the search for ways to reduce radiation exposure in patients without compromising diagnostic efficacy. To this end, good practice guidelines have been established, special applications have been developed for scanners, and research has been undertaken to optimize the clinical use of CT. Noteworthy technical developments incorporated in scanners include the different modes of X-ray tube current modulation, automatic selection of voltage settings, selective organ protection, adaptive collimation, and iterative reconstruction. The appropriate use of these tools to reduce radiation doses requires thorough knowledge of how they work.

Radiation exposure in multidetector CT: dose comparison between late 1990s and early 2010s in Korea

The effective dose under ordinary clinical computed tomography (CT) protocols using three kinds of 64-channel and a 40-channel CT ranged from 0.6 to 15.5 mSv in early 2010s. And the organ dose ranged from 1.6 to 130.4 mGy: orbital and brain doses for brain stroke CT were the highest. For the comparison of the effective dose between late 1990s and early 2010s, multidetector CT (MDCT) for high-resolution lung CT was 2.4 times higher than that of single-detector CT (SDCT) and the ratio was the highest. However, the effective dose at MDCT was 20 % lower than that of SDCT in chest CT due to applying dose-saving techniques. In organ dose comparisons, high-resolution lung CT at MDCT was 3.5-4.5 times higher than that of SDCT, and showed 1.1-1.5 times higher than that of SDCT in the head and chest CT. For the abdomen CT, the primary organ dose at MDCT was ∼30 % lower than that of SDCT.

Dose and image quality of high-pitch dual source computed tomography for the evaluation of cervical lymph node status - comparison to regular 128-slice single source computed tomography

PURPOSE

A high-pitch dual-source CT (DSCT) was compared to a standard single-source CT protocol in terms of dose and image quality for malignant lymphoma staging.

MATERIALS AND METHODS

Data from 43 patients who underwent DSCT (group 1) of the neck for staging of malignant lymphoma and 40 patients who underwent regular single source CT (group 2) were investigated retrospectively. Volume CT dose index (CTDIvol), dose length product (DLP), background noise (BN), attenuation values, signal-to-noise-ratio (SNR), scan time, effective tube current-time product (eff. mAs), subjective diagnostic image quality and artifact burden were compared.

RESULTS

CTDIvol (5.5 ± 0.8 mGy vs. 12.4 ± 1.4 mGy), DLP (172 ± 27 mGycm vs. 344 ± 60 mGycm, p<0.0001), eff. mAs (98 ± 15 mAs vs. 183 ± 20 mAs, p<0.0001) and scan time (0.64 ± 0.05 s vs. 8.21 ± 0.72 s) were lower for group 1. BN was higher (p<0.001) for group 1 with a mean difference of 2.6 HU. SNR for sternocleidomastoid and pectoral muscle was lower (6.6-12.3 vs. 7.8-19.1) for group 1. Subjective image quality (1.55 ± 0.6 vs. 1.42 ± 0.5) and artifact burden (1.62 ± 1.0 vs. 1.57 ± 0.9) were not rated significantly different (p=0.47 and p=0.80) with a good inter-observer agreement (κ=0.59-0.90).

CONCLUSION

High-pitch DSCT allows reduction of patient dose for cervical lymphoma staging while diagnostic image quality is preserved.

A review of patient dose and optimisation methods in adult and paediatric CT scanning

An increasing number of publications and international reports on computed tomography (CT) have addressed important issues on optimised imaging practice and patient dose. This is partially due to recent technological developments as well as to the striking rise in the number of CT scans being requested. CT imaging has extended its role to newer applications, such as cardiac CT, CT colonography, angiography and urology. The proportion of paediatric patients undergoing CT scans has also increased. The published scientific literature was reviewed to collect information regarding effective dose levels during the most common CT examinations in adults and paediatrics. Large dose variations were observed (up to 32-fold) with some individual sites exceeding the recommended dose reference levels, indicating a large potential to reduce dose. Current estimates on radiation-related cancer risks are alarming. CT doses account for about 70% of collective dose in the UK and are amongst the highest in diagnostic radiology, however the majority of physicians underestimate the risk, demonstrating a decreased level of awareness. Exposure parameters are not always adjusted appropriately to the clinical question or to patient size, especially for children. Dose reduction techniques, such as tube-current modulation, low-tube voltage protocols, prospective echocardiography-triggered coronary angiography and iterative reconstruction algorithms can substantially decrease doses. An overview of optimisation studies is provided. The justification principle is discussed along with tools that assist clinicians in the decision-making process. There is the potential to eliminate clinically non-indicated CT scans by replacing them with alternative examinations especially for children or patients receiving multiple CT scans.

Adult patient radiation doses from non-cardiac CT examinations: a review of published results

OBJECTIVES

CT is a valuable tool in diagnostic radiology but it is also associated with higher patient radiation doses compared with planar radiography. The aim of this article is to review patient dose for the most common types of CT examinations reported during the past 19 years.

METHODS

Reported dosimetric quantities were compared with the European diagnostic reference levels (DRLs). Effective doses were assessed with respect to the publication year and scanner technology (i.e. single-slice vs multislice).

RESULTS

Considerable variation of reported values among studies was attributed to variations in both examination protocol and scanner design. Median weighted CT dose index (CTDI(w)) and dose length product (DLP) are below the proposed DRLs; however, for individual studies the DRLs are exceeded. Median reported effective doses for the most frequent CT examinations were: head, 1.9 mSv (0.3-8.2 mSv); chest, 7.5 mSv (0.3-26.0 mSv); abdomen, 7.9 mSv (1.4-31.2 mSv); and pelvis, 7.6 mSv (2.5-36.5 mSv).

CONCLUSION

The introduction of mechanisms for dose reduction resulted in significantly lower patient effective doses for CT examinations of the head, chest and abdomen reported by studies published after 1995. Owing to the limited number of studies reporting patient doses for multislice CT examinations the statistical power to detect differences with single-slice scanners is not yet adequate.

Patient dose considerations in computed tomography examinations

Ionizing radiation is extensively used in medicine and its contribution to both diagnosis and therapy is undisputable. However, the use of ionizing radiation also involves a certain risk since it may cause damage to tissues and organs and trigger carcinogenesis. Computed tomography (CT) is currently one of the major contributors to the collective population radiation dose both because it is a relatively high dose examination and an increasing number of people are subjected to CT examinations many times during their lifetime. The evolution of CT scanner technology has greatly increased the clinical applications of CT and its availability throughout the world and made it a routine rather than a specialized examination. With the modern multislice CT scanners, fast volume scanning of the whole human body within less than 1 min is now feasible. Two dimensional images of superb quality can be reconstructed in every possible plane with respect to the patient axis (e.g. axial, sagital and coronal). Furthermore, three-dimensional images of all anatomic structures and organs can be produced with only minimal additional effort (e.g. skeleton, tracheobronchial tree, gastrointestinal system and cardiovascular system). All these applications, which are diagnostically valuable, also involve a significant radiation risk. Therefore, all medical professionals involved with CT, either as referring or examining medical doctors must be aware of the risks involved before they decide to prescribe or perform CT examinations. Ultimately, the final decision concerning justification for a prescribed CT examination lies upon the radiologist. In this paper, we summarize the basic information concerning the detrimental effects of ionizing radiation, as well as the CT dosimetry background. Furthermore, after a brief summary of the evolution of CT scanning, the current CT scanner technology and its special features with respect to patient doses are given in detail. Some numerical data is also given in order to comprehend the magnitude of the potential radiation risk involved in comparison with risk from exposure to natural background radiation levels.

Regional survey of CT dose indices in India

This study intends to evaluate the current level of computed tomography (CT) scanner doses installed in a region in India. In-site CT dose measurement was performed for 127 CT scanners in a region in India. CT dose index (CTDI) was measured using a 10 cm3 pencil ion chamber and 32-cm polymethyl methacrylate body phantom. The CT numbers and image noise were measured for the phantom using software available on each CT scanner. Of the 127 CT scanners, 13 were conventional, 53 helical single-section, 44 multidetector row CT (MDCT) and 17 refurbished machines. The mean-weighted CTDI (CTDI(w)) values calculated using standard exposure parameters for conventional, conventional refurbished, single-section helical scanner (SSHS), refurbished SSHS and MDCT scanners were 7.5, 6.53, 6.8, 6.6 and 7.04 mGy. Twenty-seven CT scanners had deranged CT numbers. Periodic quality assurance and regional dose surveys would be beneficial to set up regional reference levels in India.

Analysis of Current Practice of CT examinations

BACKGROUND

The number of CT examinations performed in Denmark increased from 14,500 examinations in 1979 to 301,617 in 2005. This implies increased radiation dose to the population. On this background, an analysis of the practice for CT examinations including potential limitations of radiation exposure and the associated risk is needed.

PURPOSES

To analyse 1) the current use of CT in a university department compared to 1996, 2) the radiation dose and risk associated with the examinations and 3) the use of CT in Denmark since 1979.

MATERIAL AND METHODS

The administrative data of CT examinations performed in the Department of Radiology, Aarhus Sygehus, during 2005 and 1996, respectively, were obtained. Additionally national CT data were obtained from the database at the National Board of Health.

RESULTS

In 1996 1,840 patients obtained 5,538 CT examinations at Aarhus Sygehus. Their mean age was 46.7 years (0-88). The most frequent referring speciality was oncology followed by abdominal surgery and orthopaedic surgery. In 2005 3,769 patients obtained 11,216 CT examinations. They were generally older with a mean age of 56.9 years (0-97). The most frequent referring speciality was oncology followed by chest medicine and abdominal surgery. In 2005 the total effective dose was 71,043 mSv (mean 18.9 mSv/per patient). According to the BEIR VII model this radiation level corresponded to a risk for inducing a cancer in 7 patients, being fatal in half of them. The national data showed a gradual increase of the number of CT examinations from 1979 to 2005, most pronounced after year 2000 coinciding with the introduction of multi-slice CT (MSCT).

CONCLUSION

The number of CT examinations at Aarhus Sygehus doubled during a 9 year period. The increase occured especially in middle and high age groups.

On the use of Monte Carlo-derived dosimetric data in the estimation of patient dose from CT examinations

The purpose of this work was to investigate the applicability and appropriateness of Monte Carlo-derived normalized data to provide accurate estimations of patient dose from computed tomography (CT) exposures. Monte Carlo methodology and mathematical anthropomorphic phantoms were used to simulate standard patient CT examinations of the head, thorax, abdomen, and trunk performed on a multislice CT scanner. Phantoms were generated to simulate the average adult individual and two individuals with different body sizes. Normalized dose values for all radiosensitive organs and normalized effective dose values were calculated for standard axial and spiral CT examinations. Discrepancies in CT dosimetry using Monte Carlo-derived coefficients originating from the use of: (a) Conversion coefficients derived for axial CT exposures, (b) a mathematical anthropomorphic phantom of standard body size to derive conversion coefficients, and (c) data derived for a specific CT scanner to estimate patient dose from CT examinations performed on a different scanner, were separately evaluated. The percentage differences between the normalized organ dose values derived for contiguous axial scans and the corresponding values derived for spiral scans with pitch = 1 and the same total scanning length were up to 10%, while the corresponding percentage differences in normalized effective dose values were less than 0.7% for all standard CT examinations. The normalized organ dose values for standard spiral CT examinations with pitch 0.5-1.5 were found to differ from the corresponding values derived for contiguous axial scans divided by the pitch, by less than 14% while the corresponding percentage differences in normalized effective dose values were less than 1% for all standard CT examinations. Normalized effective dose values for the standard contiguous axial CT examinations derived by Monte Carlo simulation were found to considerably decrease with increasing body size of the mathematical phantom used. When the body-mass index was increased from 23.0 to 32.7 kg/m2 discrepancies in patient effective dose were up to 34%. The error in estimating effective dose from a CT exposure performed on a specific CT scanner using Monte Carlo data derived for a different CT scanner was estimated to be up to 25%. A simple method was proposed and validated for the determination of scanner-specific normalized dosimetric data from data derived from Monte Carlo simulation of a specific scanner. In conclusion, computed tomography dose index (CTDI) to effective dose conversion coefficients derived by Monte Carlo simulation of axial CT scans may provide a good approximation of corresponding coefficients applicable in helical scans. However, the use of Monte Carlo conversion coefficients for the estimation of patient dose from a CT examination involves a remarkable inaccuracy when the body size of the mathematical anthropomorphic phantom used in Monte Carlo simulation differs from the body of the patient. Therefore, separate sets of Monte Carlo dosimetric CT data shall be generated for different patient body sizes. Besides calculation of different sets of Monte Carlo data for each commercially available scanner is not necessary, since scanner specific data may be derived with acceptable accuracy from the Monte Carlo data calculated for a specific scanner appropriately modified for the different CTDI(W)/CTDI(air) ratio.

A survey of awareness of radiation dose among health professionals in Northern Ireland

Increasing concern has recently been expressed in the literature that the referring doctor's knowledge of radiation doses incurred during radiological procedures is inadequate. Such information may be particularly relevant when the expansion of imaging technology is considered. To assess this, a survey was conducted of the awareness of radiation dose and risk among health professionals in Northern Ireland. A questionnaire was circulated to 300 consultants and 200 junior doctors selected randomly from a range of specialties. Participants were asked about the radiation dose from a chest radiograph, the annual dose from background radiation, and to estimate the radiation dose and cancer risk from several common radiological procedures. In total, 153 questionnaires were returned. A mean score of 7.1 out of 18 was achieved (39%). 26% of doctors achieved a score of 50% or more, and 20% of respondents knew the effective dose of a chest radiograph. 52 doctors had received formal training about ionizing radiation, and these participants scored more highly than those with no previous training in this area (p = 0.003). Our survey confirmed that clinician awareness of radiation doses imparted during common radiological procedures, and the consequent risk to the individual patient, is poor. It identified that training does increase awareness about radiation dose. There is a need to educate clinicians about (i) ionizing radiation relevant to medical imaging, given their legal responsibility as referrers under the Ionizing Radiation (Medical Exposure) regulations in the UK, and (ii) their clinical role to provide accurate information to their patients.

Major trauma & cervical clearance radiation doses & cancer induction

AIM

To compare the radiation dose of cervical spine clearance and body CT in a cohort of unconscious, major trauma patients for three different protocols, comparing spiral to multislice CT. To quantify the radiation exposure effect of the protocols on the lifetime cancer risk.

METHOD

The hospital trauma database was used to find the unconscious (GCS<9), severely injured (Injury Severity Score >15) from 1 January 2001 to 31 December 2003, excluding isolated head injuries. The protocols used for imaging the brain and cervical spine were, including the radiographs performed as a mode: The exposure factors and field of view used were put into the Monte Carlo software, to estimate the CT and radiographic X-ray doses to the body as a whole and the dose to the thyroid associated with each region imaged. The associated nominal additional lifetime cancer risk was assessed.

RESULTS

Excluding inter hospital transfers, where data was incomplete, 87 patients survived to be admitted and fulfilled the criteria. In 30 cases, the CT films were missing, the exposure factors were not recorded or no imaging was performed. In a further 21 cases, the X-ray packets were missing. Three patients had brain and cervico-dorsal CT imaging only, leaving 33 cases for evaluation. The effective radiation dose for a spiral CT of the brain using the Toshiba Xpress GX CT scanner was 3.8 mSv. The total effective doses for imaging the brain and cervical spine using the three protocols with the same CT scanner were (S.D. as % of mean): (1) 4.4 mSv (5%), (2) 7.1 mSv (10%) and (3) 8.2 mSv (15%). The corresponding mean thyroid doses were: (1) 8.5 mGy (25%), (2) 48.9 mGy (20%) and (3) 66.5 mSv (20%). The resultant nominal lifetime cancer risks were: (1) 1:4500, (2) 1:2800 and (3) 1:2400. For the Siemens Sensation 16 multislice CT scanner, the total effective doses (S.D. as % of mean) were: (1) 2.3 mSv (10%), (2) 4.3 mSv (25%) and (3) 5.4 mSv (35%). The mean doses to the thyroid were: (1) 5.9 mGy (30%), (2) 36.1 mGy (50%) and (3) 52.4 mGy (40%). The lifetime cancer risks were: (1) 1:8700, (2) 1:4600 and (3) 1:3700. Using the Toshiba spiral CT scanner, the total dose and additional lifetime nominal cancer risk associated with CT of the chest, abdomen and pelvis (CAP) as 16 mSv and 1:1250, respectively. Using the Siemens multislice CT scanner, these were 11.8 mSv and 1:1700. The cancer risk for protocol 1 when combined with a CT scan of the chest, abdomen and pelvis was 1:1000 for the spiral CT scanner and 1:1500 for the multislice CT (MCT) scanner. The cancer risk for protocol 2 with CAP CT using the MCT was 1:1200. The cancer risk for protocol 3 when combined with a CT scan of the chest, abdomen and pelvis was 1:1100 for the multislice CT scanner. Prior to the introduction of the BTS guidelines for cervical clearance, 12% of cases had CT of the body, which increased to 16% post-guidelines.

CONCLUSIONS

CT of the trunk (chest, abdomen and pelvis) is associated with the greatest risk of inducing a fatal cancer in the severely injured patient with a GCS less than 9. In our institution the multislice CT protocols expose the patient to less radiation than single slice CT, which is contrary to much of the published work to date. CT scanning the thyroid (or whole cervical spine) still has a marked effect on the cancer risk in cervical clearance. Many centres will relax cervical spinal precautions in unconscious trauma patients if the cervical spine CT with reconstructions is normal. CT of the whole cervical spine may be justified in the unconscious, severely injured patient. In conscious trauma patients, the additional lifetime risk may not justify CT of the whole cervical spine as a routine practice.

Radiation dose estimates in dual-source computed tomography coronary angiography

The purpose of this study was to quantify radiation dose parameters of dual-source CT coronary angiography. Eighty patients underwent contrast-enhanced, retrospectively ECG-gated dual-source CT coronary angiography with heart rate-adapted ECG pulsing using two algorithms: In 40 patients, the tube current was reduced to 20% (A(min1)) of the normal tube current (A(max)) outside the pulsing window; in 40 patients tube current was reduced to 4% (A(min2)) of A(max). Mean CTDI(vol) in the A(min1) group was 45.1 +/- 3.6 mGy; the mean CTDI(vol) in the A(min2) group was 39.1 +/- 3.2 mGy, with CTDI(vol) in the A(min2) group being significantly reduced when compared to the A(min1) group (P < 0.001). A significant negative correlation was found between CTDI(vol) and heart rate in group A(min1) (r = -0.82, P < 0.001), whereas no correlation was found between CTDI(vol) and heart rate in group A(min2) (r = -0.066). Using the conversion coefficient for the chest, dual-source CT coronary angiography resulted in an estimated mean effective dose of 8.8 mSv in the A(min1) group and 7.8 mSv in the A(min2). Radiation exposure of dual-source CT coronary angiography using an ECG-pulsing protocol reducing the tube current to 20% significantly decreases with increasing heart rates, despite using wider pulsing windows at higher heart rates. When using a protocol with reduced tube current of 4%, the radiation dose is significantly lower, irrespective of the heart rate.

Imaging in local staging of gastric cancer: a systematic review

PURPOSE

Endoscopic ultrasound (EUS) has been established as the diagnostic modality of choice in local (T) staging of gastric cancer. Multidetector row computed tomography (MDCT) and magnetic resonance imaging (MRI) are promising alternatives. The aim of this study was to systematically review the literature regarding the performance of each of these imaging modalities.

METHODS

A systematic search for relevant studies was performed in the PubMed/MEDLINE and EMBASE databases. Two reviewers independently assessed the methodological quality of each study. Local staging performance of included studies was calculated.

RESULTS

Twenty-two EUS studies, five MDCT studies, one combined EUS and MDCT study, and three MRI studies met the inclusion criteria. The studies were of moderate methodological quality. Diagnostic accuracy of overall T staging for EUS, MDCT, and MRI varied between 65% to 92.1%, 77.1% to 88.9%, and 71.4% to 82.6%, respectively. Sensitivity for assessing serosal involvement for EUS, MDCT, and MRI varied between 77.8% to 100%, 82.8% to 100%, and 89.5% to 93.1%, respectively. Specificity for assessing serosal involvement for EUS, MDCT, and MRI varied between 67.9% to 100%, 80% to 96.8%, and 91.4% to 100%, respectively.

CONCLUSION

EUS, MDCT, and MRI achieve similar results in terms of diagnostic accuracy in T staging and in assessing serosal involvement. Most experience has been gained with EUS. Few MDCT studies and even fewer MRI studies are available. Thus, EUS remains the first-choice imaging modality in preoperative T staging of gastric cancer.

National survey of doses from CT in the UK: 2003

A review of patient doses from CT examinations in the UK for 2003 has been conducted on the basis of data received from over a quarter of all UK scanners, of which 37% had multislice capability. Questionnaires were employed to collect scan details both for the standard protocols established at each scanner for 12 common types of CT examination on adults and children, and for samples of individual patients. This information was combined with published scanner-specific CT dose index (CTDI) coefficients to estimate values of the standard dose indices CTDI(w) and CTDI(vol) for each scan sequence. Knowledge of each scan length allowed assessment of the dose-length product (DLP) for each examination, from which effective doses were then estimated. When compared with a previous UK survey for 1991, wide variations were still apparent between CT centres in the doses for standard protocols. The mean UK doses for adult patients were in general lower by up to 50% than those for 1991, although doses were slightly higher for multislice (4+) (MSCT) relative to single slice (SSCT) scanners. Values of CTDI(vol) for MSCT were broadly similar to European survey data for 2001. The third quartile values of these dose distributions have been used to derive UK national reference doses for examinations on adults (separately for SSCT and MSCT) and children as initial tools for promoting patient protection. The survey has established the PREDICT (Patient Radiation Exposure and Dose in CT) database as a sustainable national resource for monitoring dose trends in CT through the ongoing collation of further survey data.

Relationship between noise, dose, and pitch in cardiac multi-detector row CT

In spiral computed tomography (CT), dose is always inversely proportional to pitch. However, the relationship between noise and pitch (and hence noise and dose) depends on the scanner type (single vs multi-detector row) and reconstruction mode (cardiac vs noncardiac). In single detector row spiral CT, noise is independent of pitch. Conversely, in noncardiac multi-detector row CT, noise depends on pitch because the spiral interpolation algorithm makes use of redundant data from different detector rows to decrease noise for pitch values less than 1 (and increase noise for pitch values > 1). However, in cardiac spiral CT, redundant data cannot be used because such data averaging would degrade the temporal resolution. Therefore, the behavior of noise versus pitch returns to the single detector row paradigm, with noise being independent of pitch. Consequently, since faster rotation times require lower pitch values in cardiac multi-detector row CT, dose is increased without a commensurate decrease in noise. Thus, the use of faster rotation times will improve temporal resolution, not alter noise, and increase dose. For a particular application, the higher dose resulting from faster rotation speeds should be justified by the clinical benefits of the improved temporal resolution.

Pratique du scanner en Suisse : fréquence et évolution temporelle

PURPOSE

This study analyzes CT examinations in Switzerland.

MATERIALS AND METHODS

Using different sources (administrative data on the equipment, a 1998 nationwide inquiry into practices, and data provided by the Swiss University Hospitals of Basel, Zurich, and Lausanne), we determined the frequency of CT examinations (hospitals and private radiologists) in 1998 according to different descriptive variables and studied the progression in CT use over time.

RESULTS

CT scanners increased by 7% between 1998 and 2004. The average annual number of CT examinations in 1998 was 46.3/1000 population, 3.4% of all radiological examinations in Switzerland in 1997-1998. The most frequent examination was CT of the skull (24%), while private radiology institutes perform more CTs of the spine. More CT examinations were performed for men than for women (sex ratio M/F=1.17). The average annual increase in CT in Swiss hospitals varied from 8% for Basel to 18% for Lausanne. Finally, the proportion of pediatric examinations was 5%; their numbers appear to be stabilizing.

CONCLUSION

There is a significant increase in CT examinations. It is hoped that our study will heighten awareness among doctors of CT examinations in order to optimize their use.

Impact of the introduction of 16-row MDCT on image quality and patient dose: phantom study and multi-centre survey

The purpose was to compare the image quality and patient dose between 4- and 16-row MDCT units and to evaluate the dispersion of the dose delivered for common clinical examinations. Four 4- and 16-row MDCT units were used in the study. Image noise levels from images of a CatPhan phantom were compared for all units using a given CTDI(vol) of 15.0+/-1.0 mGy. Standard acquisition protocols from ten centres, shifted from 4- to 16-row MDCT (plus one additional centre for 16-row MDCT), were compared for cerebral angiography and standard chest and abdomen examinations. In addition, the protocols used with 16-row MDCT units for diagnosis of the unstable shoulder and for cardiac examinations were also compared. The introduction of 16-MSCT units did not reduce the performance of the detectors. Concerning the acquisition protocols, a wide range in practice was observed for standard examinations; DLP varied from 800 to 5,120 mGy x cm, 130 to 860 mGy x cm, 410 to 1,790 mGy x cm and 850 to 2,500 mGy x cm for cerebral angiography, standard chest, standard abdomen and heart examinations, respectively. The introduction of 16-row MDCT did not, on average, increase the patient dose for standard chest and abdominal examinations. However, a significant dose increase has been observed for cerebral angiography. There is a wide dispersion in the doses delivered, especially for cardiac imaging.

Patient doses in multi-slice CT and the importance of optimisation

Substantive surveys of patient doses arising from CT examinations have been conducted in our Hospital. In the first instance doses were measured on a single-slice Siemens Plus 4 scanner. A similar survey was conducted initially following commissioning of a Siemens multi-slice Sensation scanner and subsequently after some effort was made to optimise scanning protocols. Doses are reported in terms of dose-length products (DLPs) and as effective doses. The optimisation process on the multi-slice scanner resulted in a reduction in DLP values by between 14% and 58%. With two exceptions, significantly lower or comparable DLP values were obtained when meaningful comparisons were made with results previously obtained with the single-slice scanner. Specific results for the multi-slice scanner in terms of the median DLP in mGy.cm (and median effective dose in mSv) are: routine brain, 660 (1.5); routine chest, 195 (4.0); chest with portal liver phase, 370 (7.2); routine chest with high resolution component, 250 (5.1); chest/abdomen/pelvis with contrast, 560 (11.0); routine abdomen without contrast, 145 (2.4); routine abdomen with contrast 215 (3.6); routine abdomen/pelvis without contrast, 230 (4.4); routine abdomen/pelvis with contrast, 345 (6.3); abdomen/pelvis triple phase, 715 (13.3); renal scan, 260 (4.6); lumbar spine, 445 (7.2); cerebral angiography, 240 (0.58); pulmonary angiography, 165 (3.4); aortic angiography, 305 (5.7). Based on the survey findings possible values for CT examination local diagnostic reference levels (LDRLs) are suggested.

Multi-slice computed tomography (MSCT): the dose challenge of the new revolution

Multislice computed tomography (MSCT) has dramatically increased the flexibility and availability of computed tomography (CT), so that the technique is being used increasingly across a widening range of applications. However CT still remains a technique with high absorbed radiation dose, and contributes an increasingly greater proportion of the total collective dose from man-made sources of radiation. Many, but not all, new applications are supported by clinical benefit. Additionally, the examination technique parameters vary widely but not always with apparent justification. There is currently a weak evidence base for reducing the absorbed dose from CT to the threshold necessary to provide clinically relevant findings and research is needed urgently in this area. In the interim, advice from guidelines such as those published by the European Commission should be followed.