Importance in optimization of multi-slice computed tomography scan protocols

Effects of the Use of Automatic Tube Current Modulation on Patient Dose and Image Quality in Computed Tomography

Objectives:

The frequency of abdominal computed tomography examinations is increasing, leading to a significant level of patient dose. This study aims to quantify and evaluate the effects of automatic tube current modulation (ATCM) technique on patient dose and image quality in contrast-enhanced biphasic abdominal examinations.

Methods:

Two different scan protocols, based on constant tube current and ATCM technique, were used on 64 patients who visited our radiology department periodically. For three patient groups with different patient size, results from two protocols were compared with respect to patient dose and image quality. Dosimetric evaluations were based on the Computed Tomography Dose Index, dose length product, and effective dose. For the comparison of image qualities between two protocols, Noise Index (NI) and Contrast to Noise Ratio (CNR) values were determined for each image. Additionally, the quality of each image was evaluated subjectively by an experienced radiologist, and the results were compared between the two protocols.

Results:

Dose reductions of 31% and 21% were achieved by the ATCM protocol in the arterial and portal phases, respectively. On the other hand, NI exhibited an increase between 9% and 46% for liver, fat and aorta. CNR values were observed to decrease between 5% and 19%. All images were evaluated by a radiologist, and no obstacle limiting a reliable diagnostic evaluation was found in any image obtained by either technique.

Conclusion:

These results showed that the ATCM technique reduces patient dose significantly while maintaining a certain level of image quality.

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

Purpose

Use of computed tomography (CT) has increased considerably all over the world. In addition, there has been an increased demand for utilisation of CT scanning in Iran over the past decade, especially after introducing multi-detector computed tomography (MDCT). It should be considered that making a mistake in the selection of scan parameters leads to patients receiving higher doses and having increased risk of cancer. All of these facts prompted us to compare six routine CT protocols in three hospitals in the city of Shiraz, and to compare the results with American College of Radiology (ACR) practice parameters and European Commission (EC) guidelines for dual- and multi-detector CT.

Material and methods

In the studied hospitals, 10 adult patients were chosen randomly for every six protocols, taken by different technologists. Seven and 11 scan factors in sequential and spiral scans, respectively, were compared with ACR (2014) and EC guidelines (EC16262 & EC2004).

Results

The majority of scan factors in sequential and the spiral protocols that were scrutinised met the guidelines. The CTDIvol and DLPs for sequential and spiral scans were lower than the dose reference level (DRL) pronounced by ACR in three CT departments, and they were compatible with the recommended dose by EC (16262) in a private hospital.

Conclusions

Based on accordance of CTDIvol with ACR measurements and incompatibility with EC (2004) in teaching hospitals, we concluded that the recorded doses should be compared with different criteria. A regular review of protocols, using special protocols for different pathologic circumstances and continual education for technologists in the three CT departments, are recommended.

Optimised paediatric CT dose at a tertiary children's hospital in Japan: a 4-y single-centre analysis

Since diagnostic reference levels (DRLs) for children are not currently established in Japan, the authors determined local DRLs for the full range of paediatric CT examinations in a single tertiary care children's hospital. A retrospective review of 4801 CT performance records for paediatric patients (<15 y old) who had undergone CT examinations from 2008 to 2011 was conducted. The most frequent examinations were of the head (52 %), followed by cardiac (15 %), temporal bone (9 %), abdomen (7 %), chest (6 %) and others (11 %). Approximately one-third of children received two or more CT scans. The authors' investigation showed that mean CTDIvol and DLP for head, chest and abdomen increased as a function of age. Benchmarking of the results showed that CTDIvol, DLP and effective dose for chest and abdomen examinations in this hospital were below average, whereas those for the head tended to be at or slightly above average of established DRL values from five countries. The results suggest that CT examinations as performed in a tertiary children's hospital in Japan are well optimised.

Reducing emergency CT radiation doses with simple techniques: A quality initiative project

INTRODUCTION

Use of indication-specific CT protocols and adjustment of scan parameters to decrease radiation exposure may result in significant dose reduction. We implemented these strategies and compare pre- and post-implementation radiation dose in emergency department (ED) patients.

METHOD

This was a descriptive, retrospective study. Patients older than 15 years who had undergone emergency CT examinations of the head, chest, abdomen, pelvis and abdominopelvic region in periods before and after dose-reduction implementation were included. The primary outcome was volume CT dose index (CTDIvol ) and dose length products (DLP).

RESULTS

There were 786 studies in the pre-implementation (group 1) and 955 studies in the post-implementation (group 2) periods. Radiation dose from all CT types significantly reduced in the post-implementation period. Average CTDIvol for head, chest, abdomen, pelvis and abdominopelvic region (doses during pre-implementation period in parentheses) were 51.5 (109), 8.1 (30.4), 13.1 (41.8), 11 (38), 11.2 (41.8) mGy, respectively. Average DLP was also significantly lower (pre-implementation dose in parentheses) in all CT types, which were 943 (2232), 324 (2517), 944 (5605), 280 (4024), 809 (7118) mGy●cm, respectively. Patients' age, gender, body mass index and size were not significantly different between the two groups. Image quality decreased but almost all examinations received an acceptable diagnostic subjective image quality.

CONCLUSION

Simple methods could help significantly reduce CT radiation exposure in ED patients while maintaining an acceptable level of diagnostic image quality.

Capture and analysis of radiation dose reports for radiology

Radiographic imaging systems can produce records of exposure and dose parameters for each patient. A variety of file formats are in use including plain text, bit map images showing pictures of written text and radiation dose structured reports as text or extended markup language files. Whilst some of this information is available with image data on the hospital picture archive and communication system, access is restricted to individual patient records, thereby making it difficult to locate multiple records for the same scan protocol. This study considers the exposure records and dose reports from four modalities. Exposure records for mammography and general radiography are utilized for repeat analysis. Dose reports for fluoroscopy and computed tomography (CT) are utilized to study the distribution of patient doses for each protocol. Results for dosimetric quantities measured by General Radiography, Fluoroscopy and CT equipment are summarised and presented in the Appendix. Projection imaging uses the dose (in air) area product and derived quantities including the dose to the reference point as a measure of the air kerma reaching the skin, ignoring movement of the beam for fluoroscopy. CT uses the dose indices CTDIvol and dose length product as a measure of the dose per axial slice, and to the scanned volume. Suitable conversion factors are identified and used to estimate the effective dose to an average size patient (for CT and fluoroscopy) and the entrance skin dose for fluoroscopy.

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.

Paediatric CT imaging trends in Australia

INTRODUCTION

The use of CT has rapidly increased since its introduction. Although an important medical tool for diagnosis and treatment, CT is recognised as being among the highest contributors to population radiation exposure. As the risks associated with exposure are higher for children than for adults, this study assessed the impact of paediatric CT in Australia by analysing imaging trends.

METHODS

CT imaging trends were derived from Medicare data. Comparable data from a dedicated paediatric hospital (Royal Children's Hospital Melbourne (RCH)) were analysed to determine the validity of utilising Medicare statistics in the younger age groups. The resulting trends reflect the situation for paediatric CT imaging in Australia.

RESULTS

In 2009, 2.1 million CT services were billed to Medicare in Australia for children and adults. The average annual growth in the number of CT services provided since 1994 was 8.5%, compared with population growth of 1.4%. Comparison of RCH and Medicare data revealed that only one third of paediatric CT imaging is captured by Medicare. Combining the data sets showed that over the last 20 years, there has been an average annual increase of 5.1% in the CT imaging rate for 0 to 18-year-olds. However, in recent years, growth in the imaging rate for 11 to 18-year-olds has slowed, while for 5 to 10-year-olds the imaging rate has declined.

CONCLUSIONS

The significant growth in CT services is attributable to increased demand from the adult demographic. Conversely, increases in the imaging rate for paediatric patients have slowed overall. In fact, for some age groups the rate has fallen.

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.

Low-dose spine CT: optimisation and clinical implementation

Spinal deformities affect young individuals predominantly girls who are usually subjected to regular and intensive radiological investigation especially before and after corrective surgery. Optimisation of spine computed tomography (CT) and the implementation of the low-dose CT in the work-up of spinal deformities were presented. The presented low-dose CT here means providing the operating surgeons with essential information about 15 vertebral bodies (almost 36-cm long region of the vertebral column). The mean effective dose of the low-dose CT was 0.37 mSv without any negative impact on image quality with regard to answering the clinical questions at issue. Tube current modulation (angular and longitudinal) has contributed to 19 % of the total dose reduction and soft tissue algorithm has helped to reduce the artefacts from the metal implants in the postoperative CTs.

Spine computed tomography doses and cancer induction

STUDY DESIGN

Computer modeling using patient computed tomography (CT) exposure data.

OBJECTIVE

To adequately consent patients, radiation dose needs to be converted into a relative risk of inducing a cancer. This article estimates different radiation doses and their relative risk of inducing a cancer from spine CT.

SUMMARY OF BACKGROUND DATA

There has been a marked increase in imaging, particularly CT, and medical exposures make up the majority of background radiation. There is little in the literature about radiation does form spine radiograph and CT imaging.

METHOD

Based on Monte Carlo simulations and the use of software designed for CT dosimetry, the anatomic region of the spine was mapped onto a mathematical phantom. The routine CT protocol was applied with corrections made to reflect the variation in radiation exposure along the length of the spine, resulting from automatic exposure control. The effective dose was calculated for each protocol and the relative risk of cancer induction calculated.

RESULTS

Risk ratio for inducing a cancer when CT scanning the whole lumbar spine was about 1 in 3200, which was much less than the risk of CTing the whole dorsal spine (about 1 in 1800) due to the longer coverage required and the anatomic implications of scanning in the region of the cervical dorsal junction. Quantitative CT of the lumbar spine is a low dose technique with estimated effective dose about 0.1 mSv with an estimated cancer risk of 1 in 200,000 compared to a typical chest radiograph estimated effective dose of 0.02 mSv, which gives a relative risk of causing cancer of about 1 in 1,000,000. Undertaking evaluation of the dorsal and lumbar markedly reduces the amount of radiation and therefore reduces the risk, for instance the estimated effective dose of CT from L3 to L5 is about 3.5 mSv, with an estimated cancer risk of 1 in 5200.

CONCLUSION

Precise CT technique of the spine, covering the smallest area necessary to answer the clinical question, has a dramatic effect on the estimated cancer risk for individual patient. Cancer risks are summative, so spine CT imaging needs to be considered in the light of the total radiation risk to the patient over their lifetime.

Radiation Dose Optimization in CT Planning of Corrective Scoliosis Surgery. A Phantom Study

The aim of the study was to explore the possibility of obtaining a helical CT scan of a long segment of vertebral column, optimally reduce the radiation dose, compare the radiation dose of the low dose helical CT with that of some of the CT protocols used in clinical practice and finally assess the impact of such a dose reduction on the image quality. A chest phantom was examined with a 16-slice CT scanner. Six scans were performed with different radiation doses. The lowest radiation dose which had no impact on image quality with regard to the information required for surgical planning of patients with scoliosis, was 20 times lower than that of routinely used protocol for CT examination of the spine in children (0.38 mSv vs 7.76 mSv). Patients with scoliosis planned for corrective spinal surgery can be examined with low dose helical CT scan. The dose reduction systems (DRS) available in modern CT scanners contribute to dose reduction and should be used.

Technical developments in radiology in Australasia dating from 1977

This article outlines the enormous technological advances that have taken place in the practice of radiology in Australasia in the 30 years since approximately 1977. These developments have led to significant improvements in image quality across all modalities, including even general radiography, which had as its genesis Roentgen's ground-breaking discovery of X-rays in 1895. However, nowhere has the development been more dramatic than in magnetic resonance imaging (MRI). This may be brought into stark reality by noting that the first MRI image of a human finger was produced in 1976 followed one year later by that of a human chest and the first MRI units were not installed in Australia and New Zealand until 1986 and 1991, respectively. The quality of these early images would be judged as laughable by today's standards where the impressive isotropic imaging that can be achieved at sub-millimetre level by both MRI and CT could not have been dreamed of 30 years ago. The review also highlights some challenges for the future of the medical physics profession.