ASSESSMENT OF EFFECTIVE DOSE FROM CONE BEAM CT IMAGING IN SPECT/CT EXAMINATION IN COMPARISON WITH OTHER MODALITIES

A systematic review and meta-analysis on the radiation dose of computed tomography in hybrid nuclear medicine imaging

BACKGROUND

While diagnostic reference levels (DRLs) are well-established for the radiopharmaceutical part, published DRLs for the CT component of positron emission tomography/computed tomography (PET/CT) and single photon emission computed tomography/computed tomography (SPECT/CT) are limited. This systematic review and meta-analysis provides an overview of the different objectives of CT in hybrid imaging and summarizes reported CT dose values for the most common PET/CT and SPECT/CT examinations. Also, an overview of already proposed national DRLs is given.

METHODS

A systematic literature search was performed to identify original articles reporting CT dose index volume (CTDIvol), dose-length product (DLP) and/or national DRLs for the most frequently performed PET/CT and/or SPECT/CT examinations. Data were grouped according to the clinical objective: diagnostic (D-CT), anatomical localisation (AL-CT) or attenuation correction (AC-CT) CT. Random-effects meta-analyses were conducted.

RESULTS

Twenty-seven articles were identified of which twelve reported national DRLs. For brain and tumour PET/CT imaging, CTDIvol and DLP values were higher for a D-CT (brain: 26.7 mGy, 483 mGy cm; tumour: 8.8 mGy, 697 mGy cm) than for an AC/AL-CT (brain: 11.3 mGy, 216 mGy cm; tumour: 4.3 mGy, 419 mGy cm). Similar conclusions were found for bone and parathyroid SPECT/CT studies: D-CT (bone: 6.5 mGy, 339 mGy cm; parathyroid: 15.1 mGy, 347 mGy cm) results in higher doses than AL-CT (bone: 3.8 mGy, 156 mGy cm; parathyroid: 4.9 mGy, 166 mGy cm). For cardiac (AC-CT), mIBG/octreotide, thyroid and post-thyroid ablation (AC/AL-CT) SPECT/CT pooled mean CTDIvol (DLP) values were 1.8 mGy (33 mGy cm), 4.6 mGy (208 mGy cm), 3.1 mGy (105 mGy cm) and 4.6 mGy (145 mGy cm), respectively. For all examinations, high variability in nuclear medicine practice was observed.

CONCLUSION

The large variation in CT dose values and national DRLs highlights the need for optimisation in hybrid imaging and justifies the clinical implementation for nuclear medicine specific DRLs.

Dose Optimization of Hybrid Imaging

Hybrid imaging combines the functional and molecular imaging of positron emission computed tomography and single-photon emission computed tomography with the anatomical information available from computed tomography and magnetic resonance imaging. As a result, the clinical utility of positron emission computed tomography/computed tomography and single-photon emission computed tomography/computed tomography has been clearly established in the past 17 y. In addition, the use of positron emission computed tomography/magnetic resonance, which was introduced to the clinic in the past decade, has continued to grow. These multimodality approaches to medical imaging have substantial dosimetric aspects associated with their practice in both adults and children. For positron emission computed tomography/computed tomography and single-photon emission computed tomography/computed tomography, one must consider the radiation dose delivered from both the radiopharmaceutical and the computed tomography portion of the hybrid scan. Whether the computed tomography is to be used solely for attenuation correction, anatomical correlation of patient, or full diagnosis must be taken into account when deciding on the computed tomography acquisition parameters. Even after 17 y, the most appropriate approach to the acquisition of these modalities is not fully established. When appropriately used, positron emission computed tomography/magnetic resonance provides the opportunity for notable dose reduction. In addition to the elimination of the radiation dose from the computed tomography, one may consider the higher sensitivity of the positron emission computed tomography component relative to that used in positron emission computed tomography/computed tomography and the longer acquisition time to reduce the amount of administered activity of the radiopharmaceutical. However, one must realize that magnetic resonance presents a different set of safety concerns outside of those associated with ionizing radiation. As with all medical procedures, the benefits as well as the potential risks of the procedure need to be evaluated in the context of choosing the most appropriate procedure to be performed and the optimization of acquisition protocol to assure high-quality clinical information with the least potential for risk possible.

A national survey of computed tomography doses in hybrid PET-CT and SPECT-CT examinations in the UK

OBJECTIVES

The aim of this study was to conduct a nationwide survey of computed tomography (CT) doses for a wide range of PET-CT and single photon emission computed tomography-computed tomography (SPECT-CT) imaging procedures, with the aim of generating proposed UK national diagnostic reference levels (NDRLs).

METHODS

CT protocol and dosimetry data for three PET-CT and seven SPECT-CT examinations were gathered from centres across the UK. Data were divided according to CT purpose (attenuation correction, localization or diagnostic) and third quartile values of scanner average dose metrics were used to generate suggested NDRLs for a range of examination and CT purpose combinations. Achievable doses were also established from the median of the dose distributions.

RESULTS

Data were obtained from 47 centres, allowing suggested NDRLs to be produced for fluorine-18-fluorodeoxyglucose half-body PET-CT, and parathyroid, post-thyroid ablation, meta-iodobenzylguanidine/octreotide, cardiac and bone SPECT-CT examinations.Variations in dose of up to a factor of 35 were observed for a given examination/CT purpose combination. For fluorine-18-fluorodeoxyglucose half-body PET-CT examination dose levels for the three CT purposes overlapped, which highlights the variability in the way in which CT purposes are interpreted across the UK. This lack of standardization is believed to be the largest contributor to the dose variations that were observed. The survey highlighted the need for targeted optimization work in many centres.

CONCLUSION

Suggested UK NDRLs and achievable doses for six common PET-CT and SPECT-CT examinations have been established as a result of this study.

Digital tomosynthesis with metal artifact reduction for assessing cementless hip arthroplasty: a diagnostic cohort study of 48 patients

OBJECTIVES

For postoperative imaging assessment of cementless hip arthroplasty, radiography and computed tomography (CT) were restricted by overlapping structures and metal artifacts, respectively. A new tomosynthesis with metal artifact reduction (TMAR) is introduced by using metal extraction and ordered subset-expectation maximization (OS-EM) reconstruction. This study investigated the effectiveness of TMAR in assessing fixation stability of cementless hip arthroplasty components.

MATERIALS AND METHODS

We prospectively included 48 consecutive patients scheduled for revision hip arthroplasty in our hospital, with 41 femoral and 35 acetabular cementless components available for evaluation. All patients took the three examinations of radiography, CT, and TMAR preoperatively, with intraoperative mechanical tests, and absence or presence of osteointegration on retrieved prosthesis as reference standards. Three senior surgeons and four junior surgeons evaluated these images independently with uniform criteria.

RESULTS

For TMAR, 82 % diagnoses on the femoral side and 84 % diagnoses on the acetabular side were accurate. The corresponding values were 44 and 67 % for radiography, and 39 % and 74 % for CT. Senior surgeons had significantly higher accuracy than junior surgeons by radiography (p < 0.05), but not by TMAR or CT.

CONCLUSIONS

By minimizing metal artifacts in the bone-implant interface and clearly depicting peri-implant trabecular structures, the TMAR technique improved the diagnostic accuracy of assessing fixation stability of cementless hip arthroplasty, and shortened the learning curve of less experienced surgeons.

LEVEL OF EVIDENCE

Level II, diagnostic cohort study.