Strategies for Reducing Radiation Exposure from Multidetector Computed Tomography in the Acute Care Setting

Ultra-low-dose computed tomography and its utility in wrist trauma in the emergency department

BACKGROUND

The use and frequency of computed tomography (CT) are increasing day by day in emergency departments (ED). This increases the amount of radiation exposed.

PURPOSE

To evaluate the image quality obtained by ultra-low-dose CT (ULDCT) in patients with suspected wrist fractures in the ED and to investigate whether it is an alternative to standard-dose CT (SDCT).

MATERIAL AND METHODS

This is a study prospectively examining 336 patients who consulted the ED for wrist trauma. After exclusion criteria were applied, the patients were divided into the study and control groups. Then, SDCT (120 kVp and 100 mAs) and ULDCT (80 kVp and 5 mAs) wrist protocols were applied simultaneously. The images obtained were evaluated for image quality and fracture independently by a radiologist and an emergency medical specialist using a 5-point scale.

RESULTS

The effective radiation dose calculated for the control group scans was 41.1 ± 2.1 µSv, whereas the effective radiation dose calculated for the study group scans was 0.5 ± 0.0 µSv. The effective radiation dose of the study group was significantly lower than that of the control group (P < 0.01). The CT images in the study group showed no significant differences in the mean image quality score between observer 1 and observer 2 (3.4 and 4.3, respectively; P = 0.58). Both observers could detect all fractures using the ULDCT images.

CONCLUSION

ULDCT provides high-quality images in wrist traumas while reducing the radiation dose by approximately 98% compared to SDCT without any changes in diagnostic accuracy.

Quantitative 3D imaging parameters improve prediction of hip osteoarthritis outcome

Osteoarthritis is an increasingly important health problem for which the main treatment remains joint replacement. Therapy developments have been hampered by a lack of biomarkers that can reliably predict disease, while 2D radiographs interpreted by human observers are still the gold standard for clinical trial imaging assessment. We propose a 3D approach using computed tomography—a fast, readily available clinical technique—that can be applied in the assessment of osteoarthritis using a new quantitative 3D analysis technique called joint space mapping (JSM). We demonstrate the application of JSM at the hip in 263 healthy older adults from the AGES-Reykjavík cohort, examining relationships between 3D joint space width, 3D joint shape, and future joint replacement. Using JSM, statistical shape modelling, and statistical parametric mapping, we show an 18% improvement in prediction of joint replacement using 3D metrics combined with radiographic Kellgren & Lawrence grade (AUC 0.86) over the existing 2D FDA-approved gold standard of minimum 2D joint space width (AUC 0.73). We also show that assessment of joint asymmetry can reveal significant differences between individuals destined for joint replacement versus controls at regions of the joint that are not captured by radiographs. This technique is immediately implementable with standard imaging technologies.

A new quantitative 3D approach to imaging of structural joint disease

Imaging of joints with 2D radiography has not been able to detect therapeutic success in research trials while 3D imaging, used regularly in the clinic, has not been approved for this purpose. We present a new 3D approach to this challenge called joint space mapping (JSM) that measures joint space width in 3D from standard clinical computed tomography (CT) data, demonstrating its analysis steps, technical validation, and reproducibility. Using high resolution peripheral quantitative CT as gold standard, we show a marginal over-estimation in accuracy of +0.13 mm and precision of ±0.32 mm. Inter-operator reproducibility bias was near-zero at −0.03 mm with limits of agreement ±0.29 mm and a root mean square coefficient of variation 7.5%. In a technical advance, we present results from across the hip joint in 3D with optimum validation and reproducibility metrics shown at inner joint regions. We also show JSM versatility using different imaging data sets and discuss potential applications. This 3D mapping approach provides information with greater sensitivity than reported for current radiographic methods that could result in improved patient stratification and treatment monitoring.

Quantitative 3D analysis of bone in hip osteoarthritis using clinical computed tomography

Objective

To assess the relationship between proximal femoral cortical bone thickness and radiological hip osteoarthritis using quantitative 3D analysis of clinical computed tomography (CT) data.

Methods

Image analysis was performed on clinical CT imaging data from 203 female volunteers with a technique called cortical bone mapping (CBM). Colour thickness maps were created for each proximal femur. Statistical parametric mapping was performed to identify statistically significant differences in cortical bone thickness that corresponded with the severity of radiological hip osteoarthritis. Kellgren and Lawrence (K&L) grade, minimum joint space width (JSW) and a novel CT-based osteophyte score were also blindly assessed from the CT data.

Results

For each increase in K&L grade, cortical thickness increased by up to 25 % in distinct areas of the superolateral femoral head–neck junction and superior subchondral bone plate. For increasing severity of CT osteophytes, the increase in cortical thickness was more circumferential, involving a wider portion of the head–neck junction, with up to a 7 % increase in cortical thickness per increment in score. Results were not significant for minimum JSW.

Conclusions

These findings indicate that quantitative 3D analysis of the proximal femur can identify changes in cortical bone thickness relevant to structural hip osteoarthritis.

Key Points

• CT is being increasingly used to assess bony involvement in osteoarthritis

• CBM provides accurate and reliable quantitative analysis of cortical bone thickness

• Cortical bone is thicker at the superior femoral head–neck with worse osteoarthritis

• Regions of increased thickness co-locate with impingement and osteophyte formation

• Quantitative 3D bone analysis could enable clinical disease prediction and therapy development

Electronic supplementary material

The online version of this article (doi:10.1007/s00330-015-4048-x) contains supplementary material, which is available to authorized users.

Advances in CT imaging for urolithiasis

Urolithiasis is a common disease with increasing prevalence worldwide and a lifetime-estimated recurrence risk of over 50%. Imaging plays a critical role in the initial diagnosis, follow-up and urological management of urinary tract stone disease. Unenhanced helical computed tomography (CT) is highly sensitive (>95%) and specific (>96%) in the diagnosis of urolithiasis and is the imaging investigation of choice for the initial assessment of patients with suspected urolithiasis. The emergence of multi-detector CT (MDCT) and technological innovations in CT such as dual-energy CT (DECT) has widened the scope of MDCT in the stone disease management from initial diagnosis to encompass treatment planning and monitoring of treatment success. DECT has been shown to enhance pre-treatment characterization of stone composition in comparison with conventional MDCT and is being increasingly used. Although CT-related radiation dose exposure remains a valid concern, the use of low-dose MDCT protocols and integration of newer iterative reconstruction algorithms into routine CT practice has resulted in a substantial decrease in ionizing radiation exposure. In this review article, our intent is to discuss the role of MDCT in the diagnosis and post-treatment evaluation of urolithiasis and review the impact of emerging CT technologies such as dual energy in clinical practice.

Addressing requests for emergency ultrasonographic examinations when implementing teleradiology services

PURPOSE

To prospectively assess how to address requests for ultrasonographic examinations when setting up an on-call teleradiology service.

MATERIALS AND METHODS

An analytical prospective study was performed from January 2012 to December 2012 inclusively. All requests received for after-hours ultrasonographic examinations during this period were analyzed. Ultrasound requests were classified as being postponable until working hours, replaceable by an alternate cross-sectional imaging modality, or urgent and needing to be performed after hours.

RESULTS

A total of 176 requests for ultrasonographic examinations were analyzed. They predominantly included requests for abdominal and pelvic ultrasonographic examinations (63%). Thirty-nine requests (22.2%) were considered as postponable, 49 (27.8%) as replaceable and 64 (36.4%) as both postponable and replaceable. Twenty-four requests (13.6%) were considered as urgent; they consisted of 10 requests for venous duplex Doppler ultrasonographic examinations of the lower limbs, eight requests for testicular ultrasonographic examinations, five for pelvic ultrasonographic examinations and one for soft-tissue ultrasonographic examination. In these urgent cases, realistic options were either to transfer the patient to another institution or to train emergency department physicians in ultrasonography for local handling.

CONCLUSION

Although the need for addressing requests for ultrasonographic examinations should be taken into account when setting up an on-call teleradiology service, it should not impede such plans.

The use of model-based iterative reconstruction to decrease ED radiation exposure

INTRODUCTION

The radiation risk posed by diagnostic computed tomography (CT) is a growing concern. The use of model-based iterative reconstruction (MBIR) technology reduces radiation exposure but requires additional processing time. The goal of this study was to compare MBIR and a standard CT reconstructive protocols in terms of emergency department (ED) visit duration and reduction in radiation exposure.

METHODS

A retrospective, matched, case-control design was used to compare patients who received MBIR and standard protocol abdomen and pelvis CTs. ED length of stay (LOS) and radiation exposure were the 2 primary outcome variables.

RESULTS

During the study period, 121 patients met inclusion criteria and were matched to controls for a total of 242 subjects. Although the low-dose group LOS was slightly longer, there was no significant difference in LOS. Mean differences were 18 minutes overall (520 vs 502 minutes; P = .497), 11 minutes for admitted patients (587 vs 576 minutes; P = .839), and 22 minutes for discharged patients (490 vs 468 minutes; P = .482). The mean volume CT dose index for the standard-dose CT was 11.6 ± 8.3 and 7.7 ± 4.6 mGy for the reduced-dose CT, a 34% decrease (P < .001).

CONCLUSION

Use of MBIR in the ED may provide decreased radiation exposure while minimally impacting ED LOS.