Andrew Tootell

Clinical evaluation of the computed tomography attenuation correction map for myocardial perfusion imaging: the potential for incidental pathology detection.

The benefits of hybrid imaging in nuclear medicine have been proven to increase the diagnostic accuracy and sensitivity of many procedures by localizing or characterizing lesions or by correcting emission data to more accurately represent radiopharmaceutical distribution. Single-photon emission computed tomography/computed tomography (SPECT/CT) has a significant role in the diagnosis and follow-up of ischaemic heart disease with attenuation correction data being obtained on an integrated CT scanner. Initially, the CT component of hybrid SPECT/CT systems was what could be described as low specification utilizing fixed output parameters. As technology has progressed, the CT component of newer systems has specifications that are identical to that of stand-alone diagnostic systems. Irrespective of the type of scanner used, the computed tomography attenuation correction (CTAC) for myocardial perfusion imaging produces low-quality, limited-range CT images of the chest that include the mediastinum, lung fields and surrounding soft tissues. The diagnostic potential of this data set is unclear; yet, examples exist whereby significant pathology can be identified and investigated further. Despite guidance from a number of professional bodies suggesting that evaluation of the resulting images for every medical exposure be carried out, there is no indication as to whether this should include the evaluation of CTAC images. This review aims to initiate discussion by examining the ethical, legal, financial and practical issues (e.g. CT specification and image quality) surrounding the clinical evaluation of the CTAC for myocardial perfusion imaging images. Reference to discussions that have taken place, and continue to take place, in other modalities, current European and UK legislations, and guidelines and research in the field will be made.

Effective lifetime radiation risk for a number of national mammography screening programmes

BACKGROUND AND PURPOSE The performance of mammography screening programmes is focussed mainly on breast cancer detection rates. However, when the benefits and risks of mammography are considered, the risk of radiation-induced cancer is calculated for only the examined breast using Mean Glandular Dose (MGD). The risk from radiation during mammography is often described as low or minimal. This study aims to evaluate the effective lifetime risk from full field digital mammography (FFDM) for a number of national screening programmes. MATERIAL AND METHODS Using an ATOM phantom, radiation doses to multiple organs were measured during standard screening mammography. Sixteen FFDM machines were used and the effective lifetime risk was calculated across the female lifespan for each machine. Once the risks were calculated using the phantom, the total effective lifetime risk across 48 national screening programmes was then calculated; this assumed that all these programmes use FFDM for screening. RESULTS Large differences exist in effective lifetime risk, varying from 42.21 [39.12-45.30] cases/106 (mean [95% CI]) in the Maltese screening programme to 1099.67 [1019.25-1180.09] cases/106 for high breast cancer risk women in the United States of America. These differences are mainly attributed to the commencement age of screening mammography and the time interval between successive screens. CONCLUSIONS Effective risk should be considered as an additional parameter for the assessment of screening mammography programme performance, especially for those programmes which recommend an early onset and more frequent screening mammography.

Effect of reconstruction methods and x-ray tube current-time product on nodule detection in an anthropomorphic thorax phantom: A crossed-modality JAFROC observer study.

Purpose: To evaluate nodule detection in an anthropomorphic chest phantom in computed tomography (CT) images reconstructed with adaptive iterative dose reduction 3D (AIDR3D) and filtered back projection (FBP) over a range of tube current–time product (mAs). Methods: Two phantoms were used in this study: (i) an anthropomorphic chest phantom was loaded with spherical simulated nodules of 5, 8, 10, and 12 mm in diameter and +100, −630, and −800 Hounsfield units electron density; this would generate CT images for the observer study; (ii) a whole-body dosimetry verification phantom was used to ultimately estimate effective dose and risk according to the model of the BEIR VII committee. Both phantoms were scanned over a mAs range (10, 20, 30, and 40), while all other acquisition parameters remained constant. Images were reconstructed with both AIDR3D and FBP. For the observer study, 34 normal cases (no nodules) and 34 abnormal cases (containing 1–3 nodules, mean 1.35 ± 0.54) were chosen. Eleven observers evaluated images from all mAs and reconstruction methods under the free-response paradigm. A crossed-modality jackknife alternative free-response operating characteristic (JAFROC) analysis method was developed for data analysis, averaging data over the two factors influencing nodule detection in this study: mAs and image reconstruction (AIDR3D or FBP). A Bonferroni correction was applied and the threshold for declaring significance was set at 0.025 to maintain the overall probability of Type I error at α = 0.05. Contrast-to-noise (CNR) was also measured for all nodules and evaluated by a linear least squares analysis. Results: For random-reader fixed-case crossed-modality JAFROC analysis, there was no significant difference in nodule detection between AIDR3D and FBP when data were averaged over mAs [F(1, 10) = 0.08, p = 0.789]. However, when data were averaged over reconstruction methods, a significant difference was seen between multiple pairs of mAs settings [F(3, 30) = 15.96, p < 0.001]. Measurements of effective dose and effective risk showed the expected linear dependence on mAs. Nodule CNR was statistically higher for simulated nodules on images reconstructed with AIDR3D (p < 0.001). Conclusions: No significant difference in nodule detection performance was demonstrated between images reconstructed with FBP and AIDR3D. mAs was found to influence nodule detection, though further work is required for dose optimization.

A phantom-based JAFROC observer study of two CT reconstruction methods: the search for optimisation of lesion detection and effective dose

Purpose: To investigate the dose saving potential of iterative reconstruction (IR) in a computed tomography (CT) examination of the thorax. Materials and Methods: An anthropomorphic chest phantom containing various configurations of simulated lesions (5, 8, 10 and 12mm; +100, -630 and -800 Hounsfield Units, HU) was imaged on a modern CT system over a tube current range (20, 40, 60 and 80mA). Images were reconstructed with (IR) and filtered back projection (FBP). An ATOM 701D (CIRS, Norfolk, VA) dosimetry phantom was used to measure organ dose. Effective dose was calculated. Eleven observers (15.11±8.75 years of experience) completed a free response study, localizing lesions in 544 single CT image slices. A modified jackknife alternative free-response receiver operating characteristic (JAFROC) analysis was completed to look for a significant effect of two factors: reconstruction method and tube current. Alpha was set at 0.05 to control the Type I error in this study. Results: For modified JAFROC analysis of reconstruction method there was no statistically significant difference in lesion detection performance between FBP and IR when figures-of-merit were averaged over tube current (F(1,10)=0.08, p = 0.789). For tube current analysis, significant differences were revealed between multiple pairs of tube current settings (F(3,10) = 16.96, p<0.001) when averaged over image reconstruction method. Conclusion: The free-response study suggests that lesion detection can be optimized at 40mA in this phantom model, a measured effective dose of 0.97mSv. In high-contrast regions the diagnostic value of IR, compared to FBP, is less clear.

Calculating individual lifetime effective risk from initial mean glandular dose arising from the first screening mammogram

OBJECTIVES The objective of the study was to use the initial mean glandular dose (MGD) arising from the first screening mammogram to estimate the individual total screening lifetime effective risk. METHODS Organ doses from full-field digital mammography (FFDM) screening exposures (craniocaudal and mediolateral oblique for each breast) were measured using a simulated approach, with average breast thickness and adult ATOM phantoms, on 16 FFDM machines. Doses were measured using thermoluminescent dosimeters accommodated inside the ATOM phantom; examined breast MGD was calculated. Total effective risk during a clients lifetime was calculated for 150 screening scenarios of different screening commencement ages and frequencies. For each scenario, a set of conversion factors were obtained to convert MGD values into total effective risk. RESULTS For the 16 FFDM machines, MGD contributes approximately 98% of total effective risk. This contribution is approximately constant for different screening regimes of different screening commencement ages. MGD contribution remains constant, but the risk reduced because the radiosensitivity of all body tissues, including breast tissue, reduces with age. Three sets of conversion factors were obtained for three screening frequencies (annual, biennial, triennial). Three relationship graphs between screening commencement age and total effective risk, as percentages of MGD, were created. CONCLUSIONS Graphical representation of total risk could be an easy way to illustrate the total effective risk during a clients lifetime. Screening frequency, commencement age, and MGD are good predictors for total effective risk, generating more understandable data for clients than MGD.

Does collimation affect patient dose in antero-posterior thoraco-lumbar spine?

INTRODUCTION The purpose of this study is to determine the effect of collimation on the lifetime attributable risk (LAR) of cancer incidence in all body organs (effective risk) in patients undergoing antero-posterior (AP) examinations of the spine. This is of particular importance for patients suffering from scoliosis as in their case regular repeat examinations are required and also because such patients are usually young and more susceptible to the effects of ionising radiation than are older patients. METHODS High sensitivity thermo-luminescent dosimeters (TLDs) were used to measure radiation dose to all organs of an adult male dosimetry phantom, positioned for an AP projection of the thoraco-lumbar spine. Exposures were made, first applying tight collimation and then subsequently with loose collimation, using the same acquisition factors. In each case, the individual TLDs were measured to determine the local absorbed dose and those representing each organ averaged to calculate organ dose. This information was then used to calculate the effective risk of cancer incidence for each decade of life from 20 to 80, and to compare the likelihood of cancer incidence when using tight and loose collimation. RESULTS The calculated figures for effective risk of cancer incidence suggest that the risk when using loose collimation compared to the use of tight collimation is over three times as high and this is the case across all age decades from 20 to 80. CONCLUSION Tight collimation can greatly reduce radiation dose and risk of cancer incidence. However collimation in scoliotic patients can be necessarily limited.

Response to letter by Faisal Alrehily

* the use of a female phantom with additional TLDs representing breasts and ovaries; * the use of the equivalent figures for females in the table produced by the National Academy of Sciences; * the use of a high kVp technique; * the use of a paediatric and/or adolescent phantom to represent younger ages; * lateral projections of the T-L spine area; each of which are likely to provide different findings compared to those in our paper.

Effective dose and Effective risk from post-SPECT imaging of the lumbar spine

Purpose Planar bone scans play an important role in the staging and monitoring of malignancy and metastases. Metastases in the lumbar spine are associated with significant morbidity, therefore accurate diagnosis is essential. Supplementary imaging after planar bone scans is often, required to characterise lesions, however, this is associated with additional radiation dose. This paper provides information on the comparative effective dose and effective risk from supplementary lumbar spine radiographs, low-dose CT (LDCT) and diagnostic CT (DCT). Method Organ dose was measured in a phantom using thermo-luminescent dosimeters. Effective dose and effective risk were calculated for radiographs, LDCT, and DCT imaging of the lumbar spine. Results Radiation dose was 0.56mSv for the antero-posterior and lateral lumbar spine radiographs, 0.80mSv for LDCT, and 3.78mSv for DCT. Additional imaging resulted in an increase in effective dose of 12.28%, 17.54% and 82.89%for radiographs, LDCT and DCT respectively. Risk of cancer induction decreased as age increased. The difference in risk between the modalities also decreased. Males had a statistically significant higher risk than female patients (p=0.023) attributed to the sensitive organs being closer to the exposed area. Conclusion Effective Dose for LDCT is comparable to radiographs of the lumbar spine. Due to the known benefits image fusion brings it is recommended that LDCT replace radiographs imaging for characterisation of lumbar spine lesions identified on planar bone scan. DCT is associated with significantly higher effective dose than LDCT. Effective risk is also higher and the difference is more marked in younger female patients.

Effective Dose and Effective Risk from Post–Single Photon Emission Computed Tomography Imaging of the Lumbar Spine

Purpose Planar bone scans play an important role in the staging and monitoring of malignancy and metastases. Metastases in the lumbar spine are associated with significant morbidity, therefore accurate diagnosis is essential. Supplementary imaging after planar bone scans is often, required to characterise lesions, however, this is associated with additional radiation dose. This paper provides information on the comparative effective dose and effective risk from supplementary lumbar spine radiographs, low-dose CT (LDCT) and diagnostic CT (DCT). Method Organ dose was measured in a phantom using thermo-luminescent dosimeters. Effective dose and effective risk were calculated for radiographs, LDCT, and DCT imaging of the lumbar spine. Results Radiation dose was 0.56mSv for the antero-posterior and lateral lumbar spine radiographs, 0.80mSv for LDCT, and 3.78mSv for DCT. Additional imaging resulted in an increase in effective dose of 12.28%, 17.54% and 82.89%for radiographs, LDCT and DCT respectively. Risk of cancer induction decreased as age increased. The difference in risk between the modalities also decreased. Males had a statistically significant higher risk than female patients (p=0.023) attributed to the sensitive organs being closer to the exposed area. Conclusion Effective Dose for LDCT is comparable to radiographs of the lumbar spine. Due to the known benefits image fusion brings it is recommended that LDCT replace radiographs imaging for characterisation of lumbar spine lesions identified on planar bone scan. DCT is associated with significantly higher effective dose than LDCT. Effective risk is also higher and the difference is more marked in younger female patients.

Research Article Effective Dose and Effective Risk from Post-Single Photon Emission Computed Tomography Imaging of the Lumbar Spine

Purpose Planar bone scans play an important role in the staging and monitoring of malignancy and metastases. Metastases in the lumbar spine are associated with significant morbidity, therefore accurate diagnosis is essential. Supplementary imaging after planar bone scans is often, required to characterise lesions, however, this is associated with additional radiation dose. This paper provides information on the comparative effective dose and effective risk from supplementary lumbar spine radiographs, low-dose CT (LDCT) and diagnostic CT (DCT). Method Organ dose was measured in a phantom using thermo-luminescent dosimeters. Effective dose and effective risk were calculated for radiographs, LDCT, and DCT imaging of the lumbar spine. Results Radiation dose was 0.56mSv for the antero-posterior and lateral lumbar spine radiographs, 0.80mSv for LDCT, and 3.78mSv for DCT. Additional imaging resulted in an increase in effective dose of 12.28%, 17.54% and 82.89%for radiographs, LDCT and DCT respectively. Risk of cancer induction decreased as age increased. The difference in risk between the modalities also decreased. Males had a statistically significant higher risk than female patients (p=0.023) attributed to the sensitive organs being closer to the exposed area. Conclusion Effective Dose for LDCT is comparable to radiographs of the lumbar spine. Due to the known benefits image fusion brings it is recommended that LDCT replace radiographs imaging for characterisation of lumbar spine lesions identified on planar bone scan. DCT is associated with significantly higher effective dose than LDCT. Effective risk is also higher and the difference is more marked in younger female patients.