Do metallic endoprostheses increase radiation dose associated with automatic tube-current modulation in abdominal-pelvic MDCT? A phantom and patient study

Factors affecting dose-length product of computed tomography component in whole-body positron emission tomography/computed tomography

In whole-body positron emission tomography (PET)/computed tomography (CT), it is important to optimise the CT radiation dose. We have investigated factors affecting the dose-length product (DLP) of the CT component of whole-body PET/CT and derived equations to predict the DLP. In this retrospective study, 1596 whole-body oncology PET/CT examinations with¹⁸F-fluorodeoxyglucose were analysed. Automatic exposure control was used to modulate radiation dose in CT. Considering age, weight, sex, arm position (up, down, one arm up), scan range (up to the mid-thigh or feet), scan mode (spiral or respiratory-triggered nonspiral) and the presence of a metal prosthesis as potential factors, multivariate analysis was performed to identify independent predictors of DLP and to determine equations to predict DLP. DLP values were predicted using the obtained equations, and compared with actual values. Among body size indices, weight best correlated with DLP in examinations performed under the standard imaging conditions (arms: up; scan range: up to the mid-thigh; scan mode: spiral; and no metal prosthesis). Multivariate analysis indicated that weight, arm position, scan range and scan mode were substantial independent predictors; lowering the arms, extending the scan range and using respiratory-triggered imaging, as well as increasing weight, increased DLP. The degree of the DLP increase tended to increase with increasing weight. The DLP values were predicted using equations that considered these parameters were in excellent agreement with the actual values. The DLP for the CT component of whole-body PET/CT is affected by weight, arm position, scan range and scan mode, and can be predicted with excellent accuracy using these factors.

An assessment of Sri Lankan radiographer's knowledge and awareness of radiation protection and imaging parameters related to patient dose and image quality in computed tomography (CT)

INTRODUCTION

As computed tomography (CT) examinations have considerably risen, safe operation is essential to reduce the patients' dose. The main objective of this study was to evaluate the level of knowledge and awareness regarding the CT exposure parameters and radiation protection in CT imaging among Sri Lankan radiographers.

METHODS

An online survey-based study was devised and distributed among the Sri Lankan CT radiographers working in 63 CT units. Questions were divided into three subsections that collected data on the participants' demographic features, knowledge of the radiation protection, and imaging parameters.

RESULTS

Eighty-eight radiographers from 32 CT units (out of 63 CT units) distributed across 11 districts (out of 27 districts) participated in this survey.The percentages of correct responses for the questions related to radiation protection, imaging parameters, noise, Diagnostic Reference Level (DRL), and CT dosimetric parameters were 71%, 79%, 87%, 50%, and 66%, respectively. Although the years of experience did not influence any of above aspects, the level of education significantly impacted the knowledge about radiation protection, exposure parameters, and noise.

CONCLUSION

The radiographer's knowledge of radiation protection and most imaging parameters associated with patient safety and image quality is satisfactory. However, findings also show that participants should fill the knowledge gap in radiation-related risks, CT exposure parameters, dosimetric parameters, and DRL.

IMPLICATIONS FOR PRACTICE

The study suggests the necessity of initiating continuous education programs for radiographers in line with national radiation protection legislation requirements that can be linked with code of practice.

Impact of Overlying Personal Items on CT Dose with Use of Automated Tube Current Modulation-Pilot Investigation

PURPOSE

To determine the incidence and impact of overlying radiopaque personal items (e.g., cellular phones, zippers) on CT dose and image quality with use of automated tube current modulation.

METHODS

Topogram images from 100 consecutive adult outpatient CT abdomen pelvis studies were retrospectively reviewed, and the number and type of overlying radiopaque personal items were recorded. Additionally, an anthropomorphic phantom was imaged with overlying personal items 1) present in topogram and axial images; 2) present in topogram but removed prior to axial acquisition; and 3) present in topogram positioned outside the field of view of the axial acquisition. dose length product (DLP) and CT dose index volume (CTDIvol) were compared to acquisitions performed without overlying personal items. Image noise was evaluated by assessing the standard deviation of Hounsfield units at the level of the overlying personal item.

RESULTS

Overlying personal items were visible in topogram images for 55% of CT exams and included underwires (38% of exams), zippers (7%), and cellular phones (1%). DLP increased when a cellular phone was present in the topogram whether or not it was removed before axial image acquisition (3.7% p = 0.002, combined AutomA and SmartmA), and image noise increased (144%, p = 0.002; AutomA). No increase in dose or image noise was observed with overlying zippers or underwires or when any object was visible in the topogram outside the field of view of the axial images.

CONCLUSIONS

Overlying personal items were observed in the majority of abdominopelvic CT scans. Large overlying radiopaque personal items resulted in increased dose and increased image noise. Removal of all overlying personal items will result in optimized dose and image quality.

Metal implants influence CT scan parameters leading to increased local radiation exposure: A proposal for correction techniques

Metal implants not only deteriorate image quality, but also increase radiation exposure. The purpose of this study was to evaluate the effect of metal hip prosthesis on absorbed radiation dose and assess the efficacy of organ dose modulation (ODM) and metal artifact reduction (MAR) protocols on dose reduction. An anthropomorphic phantom was scanned with and without bilateral metal hip prostheses, and surface and deep level radiation doses were measured at the abdomen and pelvis. Finally, the absorbed radiation doses at pelvic and abdominal cavities in the reference, ODM, and two MAR scans (Gemstone spectral imaging, GE) were compared. The Mann Whitney-U test and Kruskal-Wallis test were performed to compare the volume CT dose index (CTDI_vol) and mean absorbed radiation doses. Unilateral and bilateral metal hip prostheses increased CTDI_VOL by 14.4% and 30.5%, respectively. MAR protocols decreased absorbed radiation doses in the pelvis. MAR showed the most significant dose reduction in the deep pelvic cavity followed by ODM. However, MAR protocols increased absorbed radiation doses in the upper abdomen. ODM significantly reduced absorbed radiation in the pelvis and abdomen. In conclusion, metal hip implants increased radiation doses in abdominopelvic CT scans. MAR and ODM techniques reduced absorbed radiation dose in abdominopelvic CT scans with metal hip prostheses.

Should the automatic exposure control system of CT be disabled when scanning patients with endoaortic stents or mechanical heart valves? A phantom study

OBJECTIVES

To estimate the impact of endoaortic stents/mechanical heart valves on the output of an automatic exposure control (AEC) system and CT radiation dose.

METHODS

In this phantom study, seven stents and two valves were scanned with varying tube voltage (80/100/120 kVp), AEC activation (enabled/disabled) and prosthesis (present/absent), for a total of 540 scans. For each prosthesis, the dose-length product (DLP) was compared between scans with the AEC enabled and disabled. Percentage confidence levels for differences due to the prosthesis were calculated.

RESULTS

Differences between results with the AEC enabled and disabled were not statistically significant (p ≥ 0.059). In the comparison with and without the prosthesis, DLP was unchanged at 80 kVp and 100 kVp, while a slight increase was observed at 120 kVp. The radiation dose varied from 1.8 mGy to 2.4 mGy without the prosthesis and from 1.8 mGy to 2.5 mGy with the prosthesis (confidence level 37-100%).

CONCLUSIONS

The effect of the prosthesis on the AEC system was negligible and not clinically relevant. Therefore, disabling the AEC system when scanning these patients is not likely to provide a benefit.

KEY POINTS

• CT-AEC system is not impaired in patients with endoaortic prostheses/heart valves. • Negligible differences may be observed only at 120 kVp. • Disabling the AEC system in these patients is not recommended.

OVERVIEW, PRACTICAL TIPS AND POTENTIAL PITFALLS OF USING AUTOMATIC EXPOSURE CONTROL IN CT: SIEMENS CARE DOSE 4D

Today, computed tomography (CT) systems routinely use automatic exposure control (AEC), which modulates the tube current. However, for optimal use, there are several aspects of an AEC system that need to be considered. The purpose of this study was to provide an overview of the Siemens CARE Dose 4D AEC system, discuss practical tips and demonstrate potential pitfalls. Two adult anthropomorphic phantoms were examined using two different Siemens CT systems. When optimising the CT radiation dose and image quality, the projection angle of the localiser, patient centring, protocol selection, scanning direction and the use of protective devices requires special attention.

Computed tomography dose optimisation in cystic fibrosis: A review

Cystic fibrosis (CF) is the most common autosomal recessive disease of the Caucasian population worldwide, with respiratory disease remaining the most relevant source of morbidity and mortality. Computed tomography (CT) is frequently used for monitoring disease complications and progression. Over the last fifteen years there has been a six-fold increase in the use of CT, which has lead to a growing concern in relation to cumulative radiation exposure. The challenge to the medical profession is to identify dose reduction strategies that meet acceptable image quality, but fulfil the requirements of a diagnostic quality CT. Dose-optimisation, particularly in CT, is essential as it reduces the chances of patients receiving cumulative radiation doses in excess of 100 mSv, a dose deemed significant by the United Nations Scientific Committee on the Effects of Atomic Radiation. This review article explores the current trends in imaging in CF with particular emphasis on new developments in dose optimisation.

Impact of an Infant Transport Mattress on CT Dose and Image Quality

RATIONALE AND OBJECTIVES

Neonates are at increased risk for cold stress and hypothermia in cool environments. An infant transport mattress (ITM) is commonly used to increase neonate temperature during transport and has been used during CT scanning. This study determined the impact of an ITM on radiation dose and image artifacts during CT scanning.

MATERIALS AND METHODS

CT images from a single clinical patient scanned with an ITM were reviewed, and observations of image artifacts were recorded. A phantom was scanned with and without the ITM while varying tube-current modulation, reconstruction method, slice thickness, metal reduction algorithm, tube voltage, and tube current. The effects of the ITM on computed tomography dose index (CTDIvol), mean Hounsfield unit (HU), and HU standard deviation were recorded.

RESULTS

The clinical patient scan demonstrated significantly decreased mean HU and increased HU standard deviation. In the phantom, the ITM increased CTDIvol 27% and induced an artifact that decreased the mean HU by 3.5 HU and increased HU standard deviation by 4.6 HU. Angular tube-current modulation, strong iterative reconstruction, thick slices, metal artifact reduction, and high mA reduced the artifact.

CONCLUSIONS

Using ITM during CT scanning is not recommended given the relatively brief scanning time, increased dose, and induced image artifacts. Based on our results, several acquisition parameters may be altered to mitigate the image artifact if an ITM is required during scanning.

A questionnaire survey reviewing radiologists' and clinical specialist radiographers' knowledge of CT exposure parameters

Objective

To review knowledge of computed tomography (CT) parameters and their influence on patient dose and image quality amongst a cohort of clinical specialist radiographers (CSRs) and examining radiologists.

Methods

A questionnaire survey was devised and distributed to a cohort of 65 examining radiologists attending the American Board of Radiology exam in Kentucky in November 2011. The questionnaire was later distributed by post to a matching cohort of Irish CT CSRs. Each questionnaire contained 40 questions concerning CT parameters and their influence on both patient dose and image quality.

Results

A response rate of 22 % (radiologists) and 32 % (CSRs) was achieved. No difference in mean scores was detected between either group (27.8 ± 4 vs 28.1 ± 4, P = 0.87) although large ranges were noted (18–36). Considerable variations in understanding of CT parameters was identified, especially regarding operation of automatic exposure control and the influence of kilovoltage and tube current on patient dose and image quality. Radiologists were unaware of recommended diagnostic reference levels. Both cohorts were concerned regarding CT doses in their departments.

Conclusions

CT parameters were well understood by both groups. However, a number of deficiencies were noted which may have a considerable impact on patient doses and limit the potential for optimisation in clinical practice.

Key points

• CT users must adapt parameters to optimise patient dose and image quality.

• The influence of some parameters is not well understood.

• A need for ongoing education in dose optimisation is identified.

Positive enteric contrast material for abdominal and pelvic CT with automatic exposure control: what is the effect on patient radiation exposure?

OBJECTIVE

To assess the effect of positive enteric contrast administration on automatic exposure control (AEC) CT radiation exposure in (1) a CT phantom, and (2) a retrospective review of patients.

MATERIALS AND METHODS

We scanned a CT phantom containing simulated bowel that was sequentially filled with water and positive enteric contrast, and recorded the mean volume CT dose index (CTDIvol). We also identified 17 patients who had undergone 2 technically comparable CT scans of the abdomen and pelvis, one with positive enteric contrast and the other with oral water. Paired Student's t-tests were used to compare the mean CTDIvol between scans performed with and without positive enteric contrast. Both the phantom and patient CT scans were performed using AEC with a fixed noise index.

RESULTS

The mean CTDIvol for the phantom with simulated bowel containing water and positive enteric contrast were 8.2 ± 0.2 mGy, and 8.7 ± 0.1 mGy (6.1% higher than water, p=0.02), respectively. The mean CTDIvol for patients scanned with oral water and with positive enteric contrast were 11.8 mGy and 13.1 mGy, respectively (p=0.003). This corresponded to a mean CTDIvol which was 11.0% higher (range: 0.0-20.7% higher) in scans with positive enteric contrast than those with oral water in patients.

CONCLUSIONS

When automatic exposure control is utilized for abdominopelvic CT, the radiation exposure, as measured by CTDIvol, is higher for scans performed with positive enteric contrast than those with oral water.

Does the amount of tagged stool and fluid significantly affect the radiation exposure in low-dose CT colonography performed with an automatic exposure control?

OBJECTIVE

To determine whether the amount of tagged stool and fluid significantly affects the radiation exposure in low-dose screening CT colonography performed with an automatic tube-current modulation technique.

METHODS

The study included 311 patients. The tagging agent was barium (n = 271) or iodine (n = 40). Correlation was measured between mean volume CT dose index (CTDI (vol)) and the estimated x-ray attenuation of the tagged stool and fluid (ATT). Multiple linear regression analyses were performed to determine the effect of ATT on CTDI (vol ) and the effect of ATT on image noise while adjusting for other variables including abdominal circumference.

RESULTS

CTDI (vol) varied from 0.88 to 2.54 mGy. There was no significant correlation between CTDI (vol) and ATT (p = 0.61). ATT did not significantly affect CTDI (vol) (p = 0.93), while abdominal circumference was the only factor significantly affecting CTDI (vol) (p < 0.001). Image noise ranged from 59.5 to 64.1 HU. The p value for the regression model explaining the noise was 0.38.

CONCLUSION

The amount of stool and fluid tagging does not significantly affect radiation exposure.

Minimal radiation dose computed tomography for measurement of cup orientation in total hip arthroplasty

We studied a computed tomography (CT) protocol with minimal radiation dose for measurements of cup orientation after total hip arthroplasty. Inclination and version angles were measured directly on cadaver pelvis fixed with an acetabular component. We performed the CT scanning on the phantom made of this model in 6 protocols as follows: tube current of 300, 100, 50, 30, 20, and 10 mA. The 30 mA protocol maintained good image quality for measurements with the smallest dose (1.1 millisievert), which corresponds to less than 2 times that of an anteroposterior radiograph of the pelvis. The differences of measured angles between direct and CT measurements on the phantom were less than 1 degrees. Measurements of cup orientation were possible by this protocol in 26 hips in 22 patients after total hip arthroplasty.

Tube current reduction in pediatric non-ECG-gated heart CT by combined tube current modulation

BACKGROUND

Dose reduction by combined tube current modulation has not been evaluated in pediatric low-dose CT.

OBJECTIVE

This study was performed to evaluate tube current reduction in non-ECG-gated heart CT angiography in children by combined tube current modulation, and to assess the effects of body weight, age, sex, and scan direction on tube current reduction.

MATERIALS AND METHODS

From September 2004 to January 2005, non-ECG-gated heart CT examinations were performed with combined tube current modulation in 50 children (median age 1 year, range 1 month to 16 years; M/F 29/21) with congenital heart disease. Sixteen-slice spiral CT studies were obtained using a weight-based low-dose protocol (80 kVp, 50-160 effective mA). CT scans were obtained in the craniocaudal direction when leg veins (n=36) were used for IV injection of contrast agent and in the caudocranial direction when arm veins (n=13) were used. In one child who underwent a Fontan operation, both arm and leg veins were used. We calculated tube current reduction by combined tube current modulation and evaluated the effects of body weight, age, sex, and scan technique on tube current reduction. The quality of CT angiography images was visually evaluated by an experienced pediatric radiologist.

RESULTS

Overall tube current reduction by combined tube current modulation was 15.8+/-11.1%. The reduction was variable among five body weight groups (9.3+/-7.9% for <4.9 kg, 14.3+/-9.3% for 5.0-9.9 kg, 16.4+/-12.5% for 10.0-19.9 kg, 25.8+/-9.8% for 20.0-39.9 kg, 15.9+/-12.7% for 40.0-59.9 kg) and was significantly different among the five groups (P=0.017). When eight children in the 40.0-59.9-kg group were excluded, age showed a significant positive correlation with tube current reduction (gamma=0.4, P=0.003). There was no significant difference in tube current reduction between boys and girls. Tube current reduction was significantly greater for the caudocranial scan (21.2+/-9.2%) than for the craniocaudal scan (14.2+/-11.3%) (P=0.049). All CT angiography images were of diagnostic quality.

CONCLUSIONS

Combined tube current modulation reduced tube current in pediatric non-ECG-gated heart CT by 15.8% without degradation of image quality. With our CT protocol, for body weights up to 39.9 kg, age showed a significant positive correlation with tube current reduction, but there was a lower dose-saving effect in children heavier than 40 kg. Tube current reduction was not affected by sex, but was affected by scan direction.

Metallic prosthesis: technique to avoid increase in CT radiation dose with automatic tube current modulation in a phantom and patients

The institutional review board approved this Health Insurance Portability and Accountability Act-compliant study protocol, with waiver of informed consent. The purpose of the study was to retrospectively evaluate the combined automatic tube current modulation technique in patients with orthopedic metallic prostheses. Five hundred abdominal-pelvic computed tomographic (CT) studies performed with combined modulation technique were reviewed to identify nine patients with metallic prostheses (mean age, 66 years; range, 35-86 years; male-female ratio, 5:4). On the basis of age and transverse abdominal images, these patients were matched with nine others with no metallic prostheses (mean age, 56 years; range, 36-72 years; male-female ratio, 4:5) who were control patients. Images were graded for extent and severity of streak artifacts (grade 1, streak artifact present but not substantially compromising evaluation of adjacent structures; grade 2, streak artifact present and slightly compromising evaluation of adjacent structures; and grade 3, streak artifact present and severely compromising evaluation of adjacent structures). Student t test was performed for statistical analysis. There was no difference in mean effective tube current-time product between study and control patients (P > .49). With automatic tube current modulation, an increase in CT dose caused by metallic prostheses can be successfully avoided.