Managing patient dose in multi-detector computed tomography(MDCT). ICRP Publication 102

Correlation of iodine uptake and perfusion parameters between dual-energy CT imaging and first-pass dual-input perfusion CT in lung cancer

To investigate the potential relationship between perfusion parameters from first-pass dual-input perfusion computed tomography (DI-PCT) and iodine uptake levels estimated from dual-energy CT (DE-CT).The pre-experimental part of this study included a dynamic DE-CT protocol in 15 patients to evaluate peak arterial enhancement of lung cancer based on time-attenuation curves, and the scan time of DE-CT was determined. In the prospective part of the study, 28 lung cancer patients underwent whole-volume perfusion CT and single-source DE-CT using 320-row CT. Pulmonary flow (PF, mL/min/100 mL), aortic flow (AF, mL/min/100 mL), and a perfusion index (PI = PF/[PF + AF]) were automatically generated by in-house commercial software using the dual-input maximum slope method for DI-PCT. For the dual-energy CT data, iodine uptake was estimated by the difference (λ) and the slope (λHU). λ was defined as the difference of CT values between 40 and 70 KeV monochromatic images in lung lesions. λHU was calculated by the following equation: λHU = |λ/(70 - 40)|. The DI-PCT and DE-CT parameters were analyzed by Pearson/Spearman correlation analysis, respectively.All subjects were pathologically proved as lung cancer patients (including 16 squamous cell carcinoma, 8 adenocarcinoma, and 4 small cell lung cancer) by surgery or CT-guided biopsy. Interobserver reproducibility in DI-PCT (PF, AF, PI) and DE-CT (λ, λHU) were relatively good to excellent (intraclass correlation coefficient [ICC]Inter = 0.8726-0.9255, ICCInter = 0.8179-0.8842; ICCInter = 0.8881-0.9177, ICCInter = 0.9820-0.9970, ICCInter = 0.9780-0.9971, respectively). Correlation coefficient between λ and AF, and PF were as follows: 0.589 (P < .01) and 0.383 (P < .05). Correlation coefficient between λHU and AF, and PF were as follows: 0.564 (P < .01) and 0.388 (P < .05).Both the single-source DE-CT and dual-input CT perfusion analysis method can be applied to assess blood supply of lung cancer patients. Preliminary results demonstrated that the iodine uptake relevant parameters derived from DE-CT significantly correlated with perfusion parameters derived from DI-PCT.

Relative atherosclerotic plaque volume by CT coronary angiography trumps conventional stenosis assessment for identifying flow-limiting lesions

The new methods for diagnosing the ischemia with coronary computed tomographic angiography (CTA) as a noninvasive test have been investigated. To compare the relative plaque volume to quantitative CTA and quantitative coronary angiography (QCA) for detecting flow-limiting coronary artery stenoses. We studied 49 patients with 55 intermediate lesions (30-69% diameter stenosis) who underwent CTA, coronary angiography (CAG), and FFR. CTA and QCA measures included lesion length, percent diameter stenosis (%DS), minimal lumen diameter (MLD), target main vessel percent plaque volume (%PV), lesion %PV, target main vessel percent lumen volume (%LV), and lesion %LV. FFR ≤0.80 was considered diagnostic of a flow-limiting lesion. The area under the receiver-operating characteristic curve (AUC) was used to determine the accuracy of detecting flow-limiting lesions. We also investigated the AUC of discrimination of flow-limiting lesion according to calcium score. Eighteen of 55 lesions (32.7%) had an FFR ≤0.80. Only vessel %PV differentiated between lesions with and without flow obstruction (67.6 vs. 62.7%, p = 0.018). The AUC for vessel %PV was greatest (0.76; 95% CI 0.61-0.87). The AUC for the discrimination of the flow-limiting lesions according to low calcium score (≤400) improved to 0.82 (95% CI 0.57-0.94). In intermediate coronary artery stenoses, vessel %PV is more accurate than conventional stenosis assessment for detecting flow-limiting lesions. In low calcium score, vessel %PV is more useful for diagnosis of ischemic heart disease compared with conventional quantitative measures.

Intra-observer and inter-observer agreements for the measurement of dual-input whole tumor computed tomography perfusion in patients with lung cancer: Influences of the size and inner-air density of tumors

Background

This study was conducted to assess intra‐observer and inter‐observer agreements for the measurement of dual‐input whole tumor computed tomography perfusion (DCTP) in patients with lung cancer.

Methods

A total of 88 patients who had undergone DCTP, which had proved a diagnosis of primary lung cancer, were divided into two groups: (i) nodules (diameter ≤3 cm) and masses (diameter >3 cm) by size, and (ii) tumors with and without air density. Pulmonary flow, bronchial flow, and pulmonary index were measured in each group. Intra‐observer and inter‐observer agreements for measurement were assessed using intraclass correlation coefficient, within‐subject coefficient of variation, and Bland–Altman analysis.

Results

In all lung cancers, the reproducibility coefficient for intra‐observer agreement (range 26.1–38.3%) was superior to inter‐observer agreement (range 38.1–81.2%). Further analysis revealed lower agreements for nodules compared to masses. Additionally, inner‐air density reduced both agreements for lung cancer.

Conclusion

The intra‐observer agreement for measuring lung cancer DCTP was satisfied, while the inter‐observer agreement was limited. The effects of tumoral size and inner‐air density to agreements, especially between two observers, should be emphasized. In future, an automatic computer‐aided segment of perfusion value of the tumor should be developed.

Radiation Doses to Patients in Interventional Coronary Procedures-Estimation of Updated National Reference Levels by Dose Audit

The objective of this study was to estimate the French national updated reference levels (RLs) for coronary angiography (CA) and percutaneous coronary intervention (PCI) by a dose audit from a large data set of unselected procedures and in standard-sized patients. Kerma-area product (PKA), air kerma at interventional point (Ka,r), fluoroscopy time (FT), and the number of registered frames (NFs) and runs (NRs) were collected from 51 229 CAs and 42 222 PCIs performed over a 12-month period at 61 French hospitals. RLs estimated by the 75th percentile in CAs and PCIs performed in unselected patients were 36 and 78 Gy.cm² for PKA, 498 and 1285 mGy for Ka,r, 6 and 15 min for FT, and 566 and 960 for NF, respectively. These values were consistent with the RLs calculated in standard-sized patients. The large difference in dose between sexes leads us to propose specific RLs in males and females. The results suggest a trend for a time-course reduction in RLs for interventional coronary procedures.

Germain J, Pandit-Taskar N, Xu XG, Bolch WE, Dauer LT. A comparison of pediatric and adult CT organ dose estimation methods

BACKGROUND

Computed Tomography (CT) contributes up to 50% of the medical exposure to the United States population. Children are considered to be at higher risk of developing radiation-induced tumors due to the young age of exposure and increased tissue radiosensitivity. Organ dose estimation is essential for pediatric and adult patient cancer risk assessment. The objective of this study is to validate the VirtualDose software in comparison to currently available software and methods for pediatric and adult CT organ dose estimation.

METHODS

Five age groups of pediatric patients and adult patients were simulated by three organ dose estimators. Head, chest, abdomen-pelvis, and chest-abdomen-pelvis CT scans were simulated, and doses to organs both inside and outside the scan range were compared. For adults, VirtualDose was compared against ImPACT and CT-Expo. For pediatric patients, VirtualDose was compared to CT-Expo and compared to size-based methods from literature. Pediatric to adult effective dose ratios were also calculated with VirtualDose, and were compared with the ranges of effective dose ratios provided in ImPACT.

RESULTS

In-field organs see less than 60% difference in dose between dose estimators. For organs outside scan range or distributed organs, a five times' difference can occur. VirtualDose agrees with the size-based methods within 20% difference for the organs investigated. Between VirtualDose and ImPACT, the pediatric to adult ratios for effective dose are compared, and less than 21% difference is observed for chest scan while more than 40% difference is observed for head-neck scan and abdomen-pelvis scan. For pediatric patients, 2 cm scan range change can lead to a five times dose difference in partially scanned organs.

CONCLUSIONS

VirtualDose is validated against CT-Expo and ImPACT with relatively small discrepancies in dose for organs inside scan range, while large discrepancies in dose are observed for organs outside scan range. Patient-specific organ dose estimation is possible using the size-based methods, and VirtualDose agrees with size-based method for the organs investigated. Careful range selection for CT protocols is necessary for organ dose optimization for pediatric and adult patients.

PATIENT DOSE DURING THERAPEUTIC ENDOSCOPIC RETROGRADE CHOLANGIOPANCREATOGRAPHY PROCEDURE

Endoscopic retrograde cholangiopancreatography (ERCP) is a standard technique for the diagnosis and treatment of disorders of the pancreas or bile ducts. The aim of this study was the measurement of the radiation dose to patients during therapeutic ERCP procedures, in order to estimate the patient effective dose (ED). Fifteen patients were studied using a fluoroscopy system equipped with automatic brightness control and pulse fluoroscopy mode. Fluoroscopy time (FT), cumulative dose (Ka,r) and air kerma-area product (PKA) were collected for ERCP procedures. The ED was calculated from PKA values. The FT was ranged from 0.68 to 5.57 min, with the mean value of 2.50 min; the Ka,r was ranged from 2.22 to 19.10 mGy, with the mean value of 7.71 mGy; and the PKA was ranged between 0.59 and 5.10 Gycm2, with the mean value of 2.03 Gycm2. The ED ranged from 0.11 to 0.97 mSv, whilst the mean and median ED values were 0.39 and 0.32 mSv, respectively. FT and radiation dose to the patients were either comparative or significantly lower than those previously reported.

A measurement-based generalized source model for Monte Carlo dose simulations of CT scans

The goal of this study is to develop a generalized source model for accurate Monte Carlo dose simulations of CT scans based solely on the measurement data without a priori knowledge of scanner specifications. The proposed generalized source model consists of an extended circular source located at x-ray target level with its energy spectrum, source distribution and fluence distribution derived from a set of measurement data conveniently available in the clinic. Specifically, the central axis percent depth dose (PDD) curves measured in water and the cone output factors measured in air were used to derive the energy spectrum and the source distribution respectively with a Levenberg-Marquardt algorithm. The in-air film measurement of fan-beam dose profiles at fixed gantry was back-projected to generate the fluence distribution of the source model. A benchmarked Monte Carlo user code was used to simulate the dose distributions in water with the developed source model as beam input. The feasibility and accuracy of the proposed source model was tested on a GE LightSpeed and a Philips Brilliance Big Bore multi-detector CT (MDCT) scanners available in our clinic. In general, the Monte Carlo simulations of the PDDs in water and dose profiles along lateral and longitudinal directions agreed with the measurements within 4%/1 mm for both CT scanners. The absolute dose comparison using two CTDI phantoms (16 cm and 32 cm in diameters) indicated a better than 5% agreement between the Monte Carlo-simulated and the ion chamber-measured doses at a variety of locations for the two scanners. Overall, this study demonstrated that a generalized source model can be constructed based only on a set of measurement data and used for accurate Monte Carlo dose simulations of patients' CT scans, which would facilitate patient-specific CT organ dose estimation and cancer risk management in the diagnostic and therapeutic radiology.

Comprehensive survey of household radon gas levels and risk factors in southern Alberta

BACKGROUND

The inhalation of naturally occurring radon (222Rn) gas from indoor air exposes lung tissue to α-particle bombardment, a highly mutagenic form of ionizing radiation that damages DNA and increases the lifetime risk of lung cancer. We analyzed household radon concentrations and risk factors in southern Alberta, including Calgary, the third-largest Canadian metropolis.

METHODS

A total of 2382 residential homes (2018 in Calgary and 364 in surrounding townships) from an area encompassing 82% of the southern Alberta population were tested for radon, per Health Canada guidelines, for at least 90 days (median 103 d) between 2013 and 2016. Participants also provided home metrics (construction year, build type, foundation type, and floor and room of deployment of the radon detector) via an online survey. Homes that were subsequently remediated were retested to determine the efficacy of radon reduction techniques in the region.

RESULTS

The average indoor air radon level was 126 Bq/m3, which equates to an effective absorbed radiation dose of 3.2 mSv/yr. A total of 1135 homes (47.6%) had levels of 100 Bq/m3 or higher, and 295 homes (12.4%) had levels of 200 Bq/m3 or higher; the range was less than 15 Bq/m3 to 3441 Bq/m3. Homes built in 1992 or later had radon levels 31.5% higher, on average, than older homes (mean 142 Bq/m3 v. 108 Bq/m3). For 90 homes with an average radon level of 575 Bq/m3 before mitigation, radon suppression successfully reduced levels to an average of 32.5 Bq/m3.

INTERPRETATION

Our findings show that radon exposure is a genuine public health concern in southern Alberta, suggest that modern building practices are associated with increased indoor air radon accumulation, legitimatize efforts to understand the consequences of radon exposure to the public, and suggest that radon testing and mitigation are likely to be impactful cancer prevention strategies.

A NEW SEMI-EMPIRICAL AMBIENT TO EFFECTIVE DOSE CONVERSION MODEL FOR THE PREDICTIVE CODE FOR AIRCREW RADIATION EXPOSURE (PCAIRE)

The Predictive Code for Aircrew Radiation Exposure (PCAIRE) is a semi-empirical code that estimates both ambient dose equivalent, based on years of on-board measurements, and effective dose to aircrew. Currently, PCAIRE estimates effective dose by converting the ambient dose equivalent to effective dose (E/H) using a model that is based on radiation transport calculations and on the radiation weighting factors recommended in International Commission on Radiological Protection (ICRP) 60. In this study, a new semi-empirical E/H model is proposed to replace the existing transport calculation models. The new model is based on flight data measured using a tissue-equivalent proportional counter (TEPC). The measured flight TEPC data are separated into a low- and a high-lineal-energy spectrum using an amplitude-weighted ¹³⁷Cs TEPC spectrum. The high-lineal-energy spectrum is determined by subtracting the low-lineal-energy spectrum from the measured flight TEPC spectrum. With knowledge of E/H for the low- and high-lineal-energy spectra, the total E/H is estimated for a given flight altitude and geographic location. The semi-empirical E/H model also uses new radiation weighting factors to align the model with the most recent ICRP 103 recommendations. The ICRP 103-based semi-empirical effective dose model predicts that there is a ∼30 % reduction in dose in comparison with the ICRP 60-based model. Furthermore, the ambient dose equivalent is now a more conservative dose estimate for jet aircraft altitudes in the range of 7-13 km (FL230-430). This new semi-empirical E/H model is validated against E/H predicted from a Monte Carlo N-Particle transport code simulation of cosmic ray propagation through the Earth's atmosphere. Its implementation allows PCAIRE to provide an accurate semi-empirical estimate of the effective dose.

EYE LENS EXPOSURE TO MEDICAL STAFF PERFORMING ELECTROPHYSIOLOGY PROCEDURES: DOSE ASSESSMENT AND CORRELATION TO PATIENT DOSE

The purpose of this study was to assess the patient exposure and staff eye dose levels during implantation procedures for all types of pacemaker therapy devices performed under fluoroscopic guidance and to investigate potential correlation between patients and staff dose levels. The mean eye dose during pacemaker/defibrillator implementation was 12 µSv for the first operator, 8.7 µSv for the second operator/nurse and 0.50 µSv for radiographer. Corresponding values for cardiac resynchronisation therapy procedures were 30, 26 and 2.0 µSv, respectively. Significant (p < 0.01) correlation between the eye dose and the kerma-area product was found for the first operator and radiographers, but not for other staff categories. The study revealed eye dose per procedure and eye dose normalised to patient dose indices for different staff categories and provided an input for radiation protection in electrophysiology procedures.

Optimal slice thickness for object detection with longitudinal partial volume effects in computed tomography

Longitudinal partial volume effects (z‐axial PVE), which occur when an object partly occupies a slice, degrade image resolution and contrast in computed tomography (CT). Z‐axial PVE is unavoidable for subslice objects and reduces their contrast according to their fraction contained within the slice. This effect can be countered using a smaller slice thickness, but at the cost of an increased image noise or radiation dose. The aim of this study is to offer a tool for optimizing the reconstruction parameters (slice thickness and slice spacing) in CT protocols in the case of partial volume effects. This optimization is based on the tradeoff between axial resolution and noise. For that purpose, we developed a simplified analytical model investigating the average statistical effect of z‐axial PVE on contrast and contrast‐to‐noise ratio (CNR). A Catphan 500 phantom was scanned with various pitches and CTDI and reconstructed with different slice thicknesses to assess the visibility of subslice targets that simulate low contrast anatomical features present in CT exams. The detectability score of human observers was used to rank the perceptual image quality against the CNR. Contrast and CNR reduction due to z‐axial PVE measured on experimental data were first compared to numerical calculations and then to the analytical model. Compared to numerical calculations, the simplified algebraic model slightly overestimated the contrast but the differences remained below 5%. It could determine the optimal reconstruction parameters that maximize the objects visibility for a given dose in the case of z‐axial PVE. An optimal slice thickness equal to three‐fourth of the object width was correctly proposed by the model for nonoverlapping slices. The tradeoff between detectability and dose is maximized for a slice spacing of half the slice thickness associated with a slice width equal to the characteristic object width.

Preclinical Pharmacokinetics and Biodistribution Studies of 89Zr-Labeled Pembrolizumab

Pembrolizumab is a humanized monoclonal antibody targeting programmed cell death protein 1 (PD-1) found on T and pro-B cells. Pembrolizumab prevents PD-1 ligation by both PD-L1 and PD-L2, preventing the immune dysregulation that otherwise occurs when T-cells encounter cells expressing these ligands. Clinically, PD-1 blockade elicits potent antitumor immune responses, and antibodies blocking PD-1 ligation, including pembrolizumab, have recently received Food and Drug Administration approval for the treatment of advanced melanoma, renal cell cancer, and non-small cell lung cancer.

METHODS

In this study, we evaluated the pharmacokinetics, biodistribution, and dosimetry of pembrolizumab in vivo, accomplished through radiolabeling with the positron emitter ⁸⁹Zr. PET imaging was used to evaluate the whole-body distribution of ⁸⁹Zr-deferoxamine (Df)-pembrolizumab in two rodent models (mice and rats). Data obtained from PET scans and biodistribution studies were extrapolated to humans to estimate the dosimetry of the tracer. As a proof of concept, the biodistribution of ⁸⁹Zr-Df-pembrolizumab was further investigated in a humanized murine model.

RESULTS

The tracer remained stable in blood circulation throughout the study and accumulated the greatest in liver and spleen tissues. Both mice and rats showed similar biodistribution and pharmacokinetics of ⁸⁹Zr-Df-pembrolizumab. In the humanized mouse model, T-cell infiltration into the salivary and lacrimal glands could be successfully visualized.

CONCLUSION

These data will augment our understanding of the pharmacokinetics and biodistribution of radiolabeled pembrolizumab in vivo, while providing detailed dosimetry data that may lead to better dosing strategies in the future. These findings further demonstrate the utility of noninvasive in vivo PET imaging to dynamically track T-cell checkpoint receptor expression and localization in a humanized mouse model.

Clinical Translation of a Click-Labeled 18F-Octreotate Radioligand for Imaging Neuroendocrine Tumors

We conducted the first-in-human study of (18)F-fluoroethyl triazole [Tyr(3)] octreotate ((18)F-FET-βAG-TOCA) in patients with neuroendocrine tumors (NETs) to evaluate biodistribution, dosimetry, and safety. Despite advances in clinical imaging, detection and quantification of NET activity remains a challenge, with no universally accepted imaging standard.

METHODS

Nine patients were enrolled. Eight patients had sporadic NETs, and 1 had multiple endocrine neoplasia type 1 syndrome. Patients received 137-163 MBq (mean ± SD, 155.7 ± 8 MBq) of (18)F-FET-βAG-TOCA. Safety data were obtained during and 24 h after radioligand administration. Patients underwent detailed whole-body PET/CT multibed scanning over 4 h with sampling of venous bloods for radioactivity and radioactive metabolite quantification. Regions of interest were defined to derive individual and mean organ residence times; effective dose was calculated with OLINDA 1.1.

RESULTS

All patients tolerated (18)F-FET-βAG-TOCA with no adverse events. Over 60% parent radioligand was present in plasma at 60 min. High tumor (primary and metastases)-to-background contrast images were observed. Physiologic distribution was seen in the pituitary, salivary glands, thyroid, and spleen, with low background distribution in the liver, an organ in which metastases commonly occur. The organs receiving highest absorbed dose were the gallbladder, spleen, stomach, liver, kidneys, and bladder. The calculated effective dose over all subjects (mean ± SD) was 0.029 ± 0.004 mSv/MBq.

CONCLUSION

The favorable safety, imaging, and dosimetric profile makes (18)F-FET-βAG-TOCA a promising candidate radioligand for staging and management of NETs. Clinical studies in an expanded cohort are ongoing to clinically qualify this agent.

Clinical evaluation of a dose monitoring software tool based on Monte Carlo Simulation in assessment of eye lens doses for cranial CT scans

INTRODUCTION

The aim of this study was to verify the results of a dose monitoring software tool based on Monte Carlo Simulation (MCS) in assessment of eye lens doses for cranial CT scans.

METHODS

In cooperation with the Federal Office for Radiation Protection (Neuherberg, Germany), phantom measurements were performed with thermoluminescence dosimeters (TLD LiF:Mg,Ti) using cranial CT protocols: (I) CT angiography; (II) unenhanced, cranial CT scans with gantry angulation at a single and (III) without gantry angulation at a dual source CT scanner. Eye lens doses calculated by the dose monitoring tool based on MCS and assessed with TLDs were compared.

RESULTS

Eye lens doses are summarized as follows: (I) CT angiography (a) MCS 7 mSv, (b) TLD 5 mSv; (II) unenhanced, cranial CT scan with gantry angulation, (c) MCS 45 mSv, (d) TLD 5 mSv; (III) unenhanced, cranial CT scan without gantry angulation (e) MCS 38 mSv, (f) TLD 35 mSv. Intermodality comparison shows an inaccurate calculation of eye lens doses in unenhanced cranial CT protocols at the single source CT scanner due to the disregard of gantry angulation. On the contrary, the dose monitoring tool showed an accurate calculation of eye lens doses at the dual source CT scanner without gantry angulation and for CT angiography examinations.

CONCLUSION

The dose monitoring software tool based on MCS gave accurate estimates of eye lens doses in cranial CT protocols. However, knowledge of protocol and software specific influences is crucial for correct assessment of eye lens doses in routine clinical use.

Follow-up CT pulmonary angiograms in patients with acute pulmonary embolism

Computed tomographic (CT) angiography is associated with a non-negligible lifetime attributable risk of cancer. The risk is considerably greater for women and younger patients. Recognizing that there are risks from radiation, the purpose of this investigation was to assess the frequency of follow-up CT angiograms in patients with acute pulmonary embolism. This was a retrospective cohort study of patients aged ≥18 years with acute pulmonary embolism seen in three emergency departments from January 2013 to December 2014. Records of all patients were reviewed for at least 14 months. Pulmonary embolism was diagnosed by CT angiography in 600 patients. At least one follow-up CT angiogram in 1 year was obtained in 141 of 600 (23.5 %). Two follow-ups in 1 year were obtained in 40 patients (6.7 %), 3 follow-ups were obtained in 15 patients (2.5 %), and 4 follow-ups were obtained in 3 patients (0.5 %). Among young women (aged ≤29 years) with pulmonary embolism, 10 of 21 (47.6 %) had at least 1 follow-up and 4 of 21 (19.0 %) had 2 or more follow-ups in 1 year. Among all patients, recurrent pulmonary embolism was diagnosed in 15 of 141 (10.6 %) on the first follow-up CT angiogram and in 6 of 40 (15.0 %) on the second follow-up. Follow-up CT angiograms were obtained in a significant proportion of patients with pulmonary embolism, including young women, the group with the highest risk. Alternative options might be considered to reduce the hazard of radiation-induced cancer, particularly in young women.

Electrocardiogram-gated coronary CT angiography dose estimates using ImPACT

The primary study objective was to assess radiation doses using a modified form of the Imaging Performance Assessment of Computed Tomography (CT) scanner (ImPACT) patient dosimetry for cardiac applications on an Aquilion ONE ViSION Edition scanner, including the Ca score, target computed tomography angiography (CTA), prospective CTA, continuous CTA/cardiac function analysis (CFA), and CTA/CFA modulation. Accordingly, we clarified the CT dose index (CTDI) to determine the relationship between heart rate (HR) and X-ray exposure. As a secondary objective, we compared radiation doses using modified ImPACT, a whole-body dosimetry phantom study, and the k-factor method to verify the validity of the dose results obtained with modified ImPACT. The effective dose determined for the reference person (4.66 mSv at 60 beats per minute (bpm) and 33.43 mSv at 90bpm) were approximately 10% less than those determined for the phantom study (5.28 mSv and 36.68 mSv). The effective doses according to the k-factor (0.014 mSv•mGy-1•cm-1; 2.57 mSv and 17.10 mSv) were significantly lower than those obtained with the other two methods. In the present study, we have shown that ImPACT, when modified for cardiac applications, can assess both absorbed and effective doses. The results of our dose comparison indicate that modified ImPACT dose assessment is a promising and practical method for evaluating coronary CTA.

Radiation Dosimetry of Whole-Body Dual-Tracer 18F-FDG and 11C-Acetate PET/CT for Hepatocellular Carcinoma

Combined whole-body dual-tracer ((18)F-FDG and (11)C-acetate) PET/CT is increasingly used for staging hepatocellular carcinoma, with only limited studies investigating the radiation dosimetry data of these scans. The aim of the study was to characterize the radiation dosimetry of combined whole-body dual-tracer PET/CT protocols.

METHODS

Consecutive adult patients with hepatocellular carcinoma who underwent whole-body dual-tracer PET/CT scans were retrospectively reviewed with institutional review board approval. OLINDA/EXM 1.1 was used to estimate patient-specific internal dose exposure in each organ. Biokinetic models for (18)F-FDG and (11)C-acetate as provided by ICRP (International Commission on Radiological Protection) publication 106 were used. Standard reference phantoms were modified to more closely represent patient-specific organ mass. With patient-specific parameters, organ equivalent doses from each CT series were estimated using VirtualDose. Dosimetry capabilities for tube current modulation protocols were applied by integrating with the latest anatomic realistic models. Effective dose was calculated using ICRP publication 103 tissue-weighting coefficients for adult male and female, respectively.

RESULTS

Fourteen scans were evaluated (12 men, 2 women; mean age ± SD, 60 ± 19.48 y). The patient-specific effective dose from (18)F-FDG and (11)C-acetate was 6.08 ± 1.49 and 1.56 ± 0.47 mSv, respectively, for male patients and 6.62 ± 1.38 and 1.79 ± 0.12 mSV, respectively, for female patients. The patient-specific effective dose of the CT component, which comprised 2 noncontrast whole-body scans, to male and female patients was 21.20 ± 8.94 and 14.79 ± 3.35 mSv, respectively. Thus, the total effective doses of the combined whole-body dual-tracer PET/CT studies for male and female patients were 28.84 ± 10.18 and 23.19 ± 4.61 mSv, respectively.

CONCLUSION

Patient-specific parameters allow for more accurate estimation of organ equivalent doses. Considering the substantial radiation dose incurred, judicious medical justification is required with every whole-body dual-tracer PET/CT referral. Although radiation risks may have less impact for the population with cancer because of their reduced life expectancy, the information is of interest and relevant for both justification, to evaluate risk/benefit, and protocol optimization.

Surgical decision-making in aortic prosthetic valve endocarditis: the influence of electrocardiogram-gated computed tomography

OBJECTIVES

The aim of this study was to investigate the value of electrocardiogram (ECG)-gated computed tomography (CT) in the surgical decision-making and preoperative evaluation in patients with aortic prosthetic valve endocarditis (PVE).

METHODS

Sixty-eight prosthetic valves in 67 patients with aortic PVE were prospectively evaluated with ECG-gated CT and transoesophageal echocardiography (TEE). Imaging findings considered indications for surgery were as follows: (i) abscess/pseudoaneurysm formation; (ii) prosthetic valve dehiscence; (iii) valve destruction with valvular regurgitation; (iv) large vegetations (>1.5 cm). The coronary arteries were evaluated with ECG-gated CT. Clinical data including surgical reports and mortality data were collected.

RESULTS

Fifty-eight of 68 cases had indication for surgery based on imaging findings (ECG-gated CT/TEE). In 8 of these cases (14%), there was indication for surgery based on CT but not on TEE findings (all had perivalvular pseudoaneurysms). In 11 cases (19%), there was indication for surgery based on TEE but not on CT findings [non-drained abscess (n = 5), prosthetic valve dehiscence (n = 4), large vegetation (n = 1), valve destruction (n = 1)]. In 31 of 32 patients with indication for preoperative coronary angiography, ECG-gated CT coronary angiography was diagnostic. In 1 patient, ECG-gated CT coronary angiography was inconclusive and invasive coronary angiography was performed.

CONCLUSIONS

In patients with aortic PVE, ECG-gated CT provides additional information over TEE regarding perivalvular extension of infection, which can influence surgical decision-making. Furthermore, ECG-gated CT provides a non-invasive coronary angiogram and can in most cases replace invasive coronary angiography in the preoperative evaluation.

Correlation between effective dose and radiological risk: general concepts

The present review aims to offer an educational approach related to the limitations in the use of the effective dose mgnitude as a tool for the quantification of doses resulting from diagnostic applications of ionizing radiation. We present a critical analysis of the quantities accepted and currently used for dosimetric evaluation in diagnostic imaging procedures, based on studies published in the literature. It is highlighted the use of these quantities to evaluate the risk attributed to the procedure and to calculate the effective dose, as well as to determine its correct use and interpretation.

Whole-Body Distribution and Radiation Dosimetry of 11C-Elacridar and 11C-Tariquidar in Humans

(11)C-elacridar and (11)C-tariquidar are new PET tracers to assess the transport activity of P-glycoprotein (adenosine triphosphate-binding cassette subfamily B, member 1 [ABCB1]) and breast cancer resistance protein (adenosine triphosphate-binding cassette subfamily G, member 2 [ABCG2]). This study investigated the whole-body distribution and radiation dosimetry of both radiotracers in humans.

METHODS

Twelve healthy volunteers (6 women, 6 men) underwent whole-body PET/CT imaging over the 90 min after injection of either (11)C-elacridar or (11)C-tariquidar. Radiation doses were calculated with OLINDA/EXM software using adult reference phantoms.

RESULTS

Biodistribution was consistent with a major elimination route of hepatobiliary excretion, which may be mediated by ABCB1 and ABCG2. High radioactivity uptake was seen in liver, followed by spleen and kidneys, whereas brain uptake was lowest. Effective doses were 3.41 ± 0.06 μSv/MBq for (11)C-elacidar and 3.62 ± 0.11 μSv/MBq for (11)C-tariquidar.

CONCLUSION

Our data indicate that both (11)C-elacridar and (11)C-tariquidar are safe radiotracers, for which an injected activity of 400 MBq corresponds to a total effective dose of approximately 1.5 mSv.

Age-related differences in image quality of prospectively ECG-triggered axial and helical scans for coronary CT angiography

We investigated the underlying reasons for the occurrence of misalignment artifacts in prospectively ECG-triggered axial coronary CT angiography scans. In this study we analyzed 56 consecutive patients scanned in axial mode and 66 consecutive patients scanned in helical mode. Predictors for the occurrence of misalignment artifacts were evaluated by multivariable logistic regression analysis for those patients scanned in the axial mode; advanced age was identified as the sole independent predictor (odds ratio: 1.088; 95 % CI: 1.012-1.170; p = 0.0228). In a comparison with the patients scanned in the helical mode, the image quality score for patients aged 65 years or older was significantly higher in helical mode than in axial mode (2.6 ± 0.5 and 2.4 ± 0.7, respectively; p = 0.0313). Misalignment artifacts in the image are more common in the elderly than in younger. Helical mode should be preferred in this older patient population to allow for good diagnostic image quality.

Doses metrics and patient age in CT

The aim of this study was to investigate how effective dose and size-specific dose estimate (SSDE) change with patient age (size) for routine head and abdominal/pelvic CT examinations. Heads and abdomens of patients were modelled as a mass-equivalent cylinder of water corresponding to the patient 'effective diameter'. Head CT scans were performed at CTDIvol(S) of 40 mGy, and abdominal CT scans were performed at CTDIvol(L) of 10 mGy. Values of SSDE were obtained using conversion factors in AAPM Task Group Report 204. Age-specific scan lengths for head and abdominal CT scans obtained from the authors' clinical practice were used to estimate the dose-length product for each CT examination. Effective doses were calculated from previously published age- and sex-specific E/DLP conversion factors, based on ICRP 103 organ-weighting factors. For head CT examinations, the scan length increased from 15 cm in a newborn to 20 cm in adults, and for an abdominal/pelvic CT, the scan length increased from 20 cm in a newborn to 45 cm in adults. For head CT scans, SSDE ranged from 37.2 mGy in adults to 48.8 mGy in a newborn, an increase of 31 %. The corresponding head CT effective doses range from 1.4 mSv in adults to 5.2 mSv in a newborn, an increase of 270 %. For abdomen CT scans, SSDE ranged from 13.7 mGy in adults to 23.0 mGy in a newborn, an increase of 68 %. The corresponding abdominal CT effective doses ranged from 6.3 mSv in adults to 15.4 mSv in a newborn, an increase of 140 %. SSDE increases much less than effective dose in paediatric patients compared with adults because it does not account for scan length or scattered radiation. Size- and age-specific effective doses better quantify the total radiation received by patients in CT by explicitly accounting for all organ doses, as well as their relative radio sensitivity.

Patient radiation biological risk in computed tomography angiography procedure

Computed tomography angiography (CTA) has become the most valuable imaging modality for the diagnosis of blood vessel diseases; however, patients are exposed to high radiation doses and the probability of cancer and other biological effects is increased. The objectives of this study were to measure the patient radiation dose during a CTA procedure and to estimate the radiation dose and biological effects. The study was conducted in two radiology departments equipped with 64-slice CT machines (Aquilion) calibrated according to international protocols. A total of 152 patients underwent brain, lower limb, chest, abdomen, and pelvis examinations. The effective radiation dose was estimated using ImPACT scan software. Cancer and biological risks were estimated using the International Commission on Radiological Protection (ICRP) conversion factors. The mean patient dose value per procedure (dose length product [DLP], mGy·cm) for all examinations was 437.8 ± 166, 568.8 ± 194, 516.0 ± 228, 581.8 ± 175, and 1082.9 ± 290 for the lower limbs, pelvis, abdomen, chest, and cerebral, respectively. The lens of the eye, uterus, and ovaries received high radiation doses compared to thyroid and testis. The overall patient risk per CTA procedure ranged between 15 and 36 cancer risks per 1 million procedures. Patient risk from CTA procedures is high during neck and abdomen procedures. Special concern should be provided to the lens of the eye and thyroid during brain CTA procedures. Patient dose reduction is an important consideration; thus, staff should optimize the radiation dose during CTA procedures.

Radiation dose of cone-beam computed tomography compared to conventional radiographs in orthodontics

OBJECTIVES

The aim of this study was to determine radiation doses of different cone-beam computed tomography (CBCT) scan modes in comparison to a conventional set of orthodontic radiographs (COR) by means of phantom dosimetry.

MATERIALS AND METHODS

Thermoluminescent dosimeter (TLD) chips (3 × 1 × 1 mm) were used on an adult male tissue-equivalent phantom to record the distribution of the absorbed radiation dose. Three different scanning modes (i.e., portrait, normal landscape, and fast scan landscape) were compared to CORs [i.e., conventional lateral (LC) and posteroanterior (PA) cephalograms and digital panoramic radiograph (OPG)].

RESULTS

The following radiation levels were measured: 131.7, 91, and 77 μSv in the portrait, normal landscape, and fast landscape modes, respectively. The overall effective dose for a COR was 35.81 μSv (PA: 8.90 μSv; OPG: 21.87 μSv; LC: 5.03 μSv).

DISCUSSION

Although one CBCT scan may replace all CORs, one set of CORs still entails 2-4 times less radiation than one CBCT. Depending on the scan mode, the radiation dose of a CBCT is about 3-6 times an OPG, 8-14 times a PA, and 15-26 times a lateral LC. Finally, in order to fully reconstruct cephalograms including the cranial base and other important structures, the CBCT portrait mode must be chosen, rendering the difference in radiation exposure even clearer (131.7 vs. 35.81 μSv). Shielding radiation-sensitive organs can reduce the effective dose considerably.

CONCLUSION

CBCT should not be recommended for use in all orthodontic patients as a substitute for a conventional set of radiographs. In CBCT, reducing the height of the field of view and shielding the thyroid are advisable methods and must be implemented to lower the exposure dose.

Effective radiation doses of CT examinations in Japan: a nationwide questionnaire-based study

OBJECTIVE

The aims of this study were to estimate the effective radiation doses from CT examinations of both adults and children in Japan and to study the impact of various scan parameters on the effective doses.

METHODS

A questionnaire, which contained detailed questions on the CT scan parameters employed, was distributed to 3000 facilities throughout Japan. For each scanner protocol, the effective doses for head (non-helical and helical), chest and upper abdomen acquisitions were estimated using ImPACT CT Patient Dosimetry Calculator software v. 1.0.4 (St George's Hospital, London, UK).

RESULTS

The mean effective doses for chest and abdominal examinations using 80-110 kV were significantly lower than those using 120 kV. However, there was no statistically significant difference in the mean effective doses for head scans between facilities employing 80-110 kV and 120 kV. In chest and abdominal examinations, the mean effective doses using CT scanners from Western manufacturers [Siemens (Forchheim, Germany), Philips (Eindhoven, Netherlands) and GE Medical Systems (Milwaukee, WI)] were significantly lower than those of examinations using Japanese scanners [Hitachi (Kashiwa, Japan) and Toshiba (Otawara, Tochigi, Japan)], except for in paediatric chest examinations.

CONCLUSION

The mean effective doses for adult head, chest and abdominal CT examinations were 2.9, 7.7 and 10.0 mSv, respectively, whereas the corresponding mean effective doses for paediatric examinations were 2.6, 7.1 and 7.7 mSv, respectively.

ADVANCES IN KNOWLEDGE

Facilities using CT scanners by Western manufacturers commonly adopt low-tube-voltage techniques, and low-tube-voltage CT may be useful for reducing the radiation doses to the patients, particularly for the body region.

Updated estimates of typical effective doses for common CT examinations in the UK following the 2011 national review

OBJECTIVE

To investigate the impact of evolving International Commission on Radiological Protection (ICRP) recommendations concerning calculation of effective dose (E) and compare updated typical UK values for common CT examinations with previous data.

METHODS

Monte Carlo simulations have provided normalized organ doses relating to 15 CT scanner models and 5 virtual reference adults. Series of representative E/dose-length product (DLP) coefficients were derived for common examinations on the separate bases of not only older stylized mathematical phantoms and voxel phantoms presently recommended by ICRP, but also the 1977, 1990 and 2007 formulations for E. Updated E/DLP coefficients were applied to typical values of DLP from the 2011 UK survey.

RESULTS

Changes in ICRP recommendations that have arisen from improving evidence on stochastic risk, influence values of E by up to a factor two for CT examinations of the head and neck, although differences for the trunk typically amount to ±10%. Adoption of the voxel rather than the mathematical phantoms used previously can lead to further changes in E by a few tens of percent. Updated typical values of E for UK CT examinations range from 2 to 20 mSv. Increases by 20-400% since 2003 arise not only from increases by 30-160% in typical values of DLP, but also increases by 30-90% in relation to E/DLP coefficients for examinations of the trunk.

CONCLUSION

Values of E, including updated typical data for UK CT, should be compared with caution in relation to their purpose and underlying factors concerning their calculation.

ADVANCES IN KNOWLEDGE

Updated E/DLP coefficients and typical values of E for UK CT, and an appreciation of factors influencing these data.

Clinical Translation of an Albumin-Binding PET Radiotracer 68Ga-NEB

Suitably labeled Evans blue dye has been successfully applied to evaluate cardiac function, vascular permeability, and lymphatic imaging in preclinical settings. This study documented the first-in-human application of 68Ga-1,4,7-triazacyclononane-N,N',N″-triacetic acid (NOTA)-NEB.

METHODS

The NOTA-conjugated truncated form of Evans blue, NEB, was labeled with 68Ga and tested in BALB/C mice for dynamic PET and ex vivo biodistribution studies. Three healthy volunteers (2 men and 1 woman) underwent 90-min whole-body dynamic PET. The absorbed doses for major organs and whole body were calculated using OLINDA/EXM software. Eleven patients with focal hepatic lesions diagnosed by enhanced CT or MR imaging were subjected to whole-body PET/CT acquisitions at 30 min after intravenous injection of 111-148 MBq (3-4 mCi) of 68Ga-NEB.

RESULTS

NEB dye was labeled with 68Ga (half-time, 68 min) with high yield and purity. After intravenous injection, 68Ga-NEB formed a complex with serum albumin, thus most of the radioactivity was retained in blood circulation. The tracer was demonstrated to be safe in both healthy volunteers and recruited patients without side effects or allergies. Among the 11 patients, hemangiomas showed much higher 68Ga-NEB signal intensity than the surrounding normal hepatic tissues, whereas no apparent difference between lesions and hepatic tissues was identified on 18F-FDG PET. All other focal hepatic lesions including hepatocellular carcinoma, hepatic cysts, and neuroendocrine tumor liver metastases showed negative 68Ga-NEB contrast to hepatic tissues.

CONCLUSION

As a blood-pool imaging agent, 68Ga-NEB is safe to use in the clinic, and our preliminary studies demonstrate the value of differentiating hepatic hemangioma from other benign or malignant focal hepatic lesions. Easy labeling with different positron emitters of various half-lives, excellent pharmacokinetics, and imaging quality warrant further clinical applications of NEB-based PET tracers.

Basis for standards: ICRP activities

The purpose of this chapter is to describe work achieved recently by the International Commission on Radiological Protection (ICRP) and especially by Committee 3 (Protection in Medicine) and its use for standards. In March 1960, the Board of Governors of the International Atomic Energy Agency approved the Agency's 'Health and Safety Measures', stating that the Agency's 'Basic Safety Standards' (BSS) would be based, to the extent possible, on the recommendations of the ICRP. In a similar way, the Council of the European Union took into account the new recommendations of the ICRP when adopting the new Directive 2013/59/EURATOM that laid down BSS for protection against the dangers arising from exposure to ionising radiation. The new limit for the lens of the eyes for occupational exposures has been incorporated into these international standards and several articles dealing with medical exposures: justification, optimisation, recording patient doses, the use of diagnostic reference levels, training, accidental and unintended exposures, etc. have also been included in agreement with the ICRP recommendations.

Effects of dose rates on radiation-induced replenishment of intestinal stem cells determined by Lgr5 lineage tracing

An understanding of the dynamics of intestinal Lgr5(+) stem cells is important for elucidating the mechanism of colonic cancer development. We previously established a method for evaluating Lgr5(+) stem cells by tamoxifen-dependent Lgr5-lineage tracing and showed that high-dose-rate radiation stimulated replenishment of colonic stem cells. In this study, we evaluated the effects of low-dose-rate radiation on stem cell maintenance. Tamoxifen (4OHT)-injected Lgr5-EGFP-IRES-Cre(ERT2) × ROSA-LSL-LacZ mice were used, LacZ-labeled colonic crypts were enumerated, and the loss of LacZ(+) crypts under low-dose-rate radiation was estimated. After 4OHT treatment, the number of LacZ-labeled Lgr5(+) stem cells was higher in the colon of infant mice than in adult mice. The percentage of LacZ-labeled crypts in infant mice rapidly decreased after 4OHT treatment. However, the percentage of labeled crypts plateaued at ∼2% at 4 weeks post-treatment and remained unchanged for up to 7 months. Thus, it will be advantageous to evaluate the long-term effects of low-dose-rate radiation. Next, we determined the percentages of LacZ-labeled crypts irradiated with 1 Gy administered at different dose rates. As reported in our previous study, mice exposed to high-dose-rate radiation (30 Gy/h) showed a marked replenishment (P = 0.04). However, mice exposed to low-dose-rate radiation (0.003 Gy/h) did not exhibit accelerated stem-cell replenishment (P = 0.47). These findings suggest the percentage of labeled crypts can serve as a useful indicator of the effects of dose rate on the stem cell pool.

Radiation environment at aviation altitudes and in space

On the Earth, protection from cosmic radiation is provided by the magnetosphere and the atmosphere, but the radiation exposure increases with increasing altitude. Aircrew and especially space crew members are therefore exposed to an increased level of ionising radiation. Dosimetry onboard aircraft and spacecraft is however complicated by the presence of neutrons and high linear energy transfer particles. Film and thermoluminescent dosimeters, routinely used for ground-based personnel, do not reliably cover the range of particle types and energies found in cosmic radiation. Further, the radiation field onboard aircraft and spacecraft is not constant; its intensity and composition change mainly with altitude, geomagnetic position and solar activity (marginally also with the aircraft/spacecraft type, number of people aboard, amount of fuel etc.). The European Union Council directive 96/29/Euroatom of 1996 specifies that aircrews that could receive dose of >1 mSv y(-1) must be evaluated. The dose evaluation is routinely performed by computer programs, e.g. CARI-6, EPCARD, SIEVERT, PCAire, JISCARD and AVIDOS. Such calculations should however be carefully verified and validated. Measurements of the radiation field in aircraft are thus of a great importance. A promising option is the long-term deployment of active detectors, e.g. silicon spectrometer Liulin, TEPC Hawk and pixel detector Timepix. Outside the Earth's protective atmosphere and magnetosphere, the environment is much harsher than at aviation altitudes. In addition to the exposure to high energetic ionising cosmic radiation, there are microgravity, lack of atmosphere, psychological and psychosocial components etc. The milieu is therefore very unfriendly for any living organism. In case of solar flares, exposures of spacecraft crews may even be lethal. In this paper, long-term measurements of the radiation environment onboard Czech aircraft performed with the Liulin since 2001, as well as measurements and simulations of dose rates on and outside the International Space Station were presented. The measured and simulated results are discussed in the context of health impact.

Optimal Scanning Protocols for Dual-Energy CT Angiography in Peripheral Arterial Stents: An in Vitro Phantom Study

OBJECTIVE

To identify the optimal dual-energy computed tomography (DECT) scanning protocol for peripheral arterial stents while achieving a low radiation dose, while still maintaining diagnostic image quality, as determined by an in vitro phantom study.

METHODS

Dual-energy scans in monochromatic spectral imaging mode were performed on a peripheral arterial phantom with use of three gemstone spectral imaging (GSI) protocols, three pitch values, and four kiloelectron volts (keV) ranges. A total of 15 stents of different sizes, materials, and designs were deployed in the phantom. Image noise, the signal-to-noise ratio (SNR), different levels of adaptive statistical iterative reconstruction (ASIR), and the four levels of monochromatic energy for DECT imaging of peripheral arterial stents were measured and compared to determine the optimal protocols.

RESULTS

A total of 36 scans with 180 datasets were reconstructed from a combination of different protocols. There was a significant reduction of image noise with a higher SNR from monochromatic energy images between 65 and 70 keV in all investigated preset GSI protocols (p < 0.05). In addition, significant effects were found from the main effect analysis for these factors: GSI, pitch, and keV (p = 0.001). In contrast, there was significant interaction on the unstented area between GSI and ASIR (p = 0.015) and a very high significant difference between keV and ASIR (p < 0.001). A radiation dose reduction of 50% was achieved.

CONCLUSIONS

The optimal scanning protocol and energy level in the phantom study were GSI-48, pitch value 0.984, and 65 keV, which resulted in lower image noise and a lower radiation dose, but with acceptable diagnostic images.

The primary study of low-dose pancreas perfusion by 640- slice helical CT: a whole-organ perfusion

To discuss the feasibility of low-dose whole-pancreas imaging utilizing 640-slice dynamic volume CT.80 patients (40 cases of normal pancreas and 40 patients supposed of having pancreatic carcinoma or focal pancreatic space-occupying lesions were mainly refered) referred for CT pancreas perfusion were enrolled in the study. 80 patients randomly assigned to 3 groups: Group ① (whole sequence). Group ② (odd number sequence). Group ③ (even number group)(Compared to ①, the scanning times and effective radiate dose of ② and ③ decreased about 50% respectively). The head, body, tail of each normal pancreas without any pancreatic disease, lesion and lesion-surrounding areas of each pancreatic cancer were selected as ROI, and tissue peak, blood flow are measured.According to pathology and clinical materials, 27 patients were diagnosed as pancreatic cancer; 40 patients were diagnosed as normal pancreas. The tissue peak and blood flow of the head, body, tail of normal pancreas without any pancreatic disease are 109.63 ± 16.60 and 131.90 ± 41.61, 104.38 ± 19.39 and 127.78 ± 42.52, 104.55 ± 15. 44 and 123.50 ± 33.44 respectively. The tissue peak and blood flow of pancreatic cancer is 59.59 ± 18.20 and 60.00 ± 15.36. For and between each group, there is no significant statistical difference for the tissue peak and blood flow of normal areas of the head, body, tail of normal pancreas. There is statistical difference for the tissue peak and blood flow of lesion and lesion-surrounding areas of pancreatic cancer in each group. However, there is no statistical difference for the tissue peak and blood flow of normal and diseasing areas between 3 groups.Low-dose whole-pancreas perfusion with 640-slice dynamic volume CT is feasible.

Diagnostic confidence of run-off CT-angiography as the primary diagnostic imaging modality in patients presenting with acute or chronic peripheral arterial disease

Objectives

To investigate the reliability of CT-angiography of the lower extremities (run-off CTA) to derive a treatment decision in patients with acute and chronic peripheral artery disease (PAD).

Materials and Methods

314 patients referred for run-off CTA were includ-ed in this retrospective study. First, diagnostic confidence of run-off CTA to derive a treat-ment decision was assessed in an interdisciplinary vascular conference using a 2 point scale (sufficient or not sufficient diagnostic confidence) and compared with the image quality eval-uated by two readers in consensus in four different levels (abdominopelvic, thigh, calf, foot arteries). Second, reliability of treatment decision was verified in all patients undergoing re-vascularization therapy.

Results

Diagnostic confidence of run-off CTA to derive a treatment deci-sion was sufficient in all patients with acute and in 97% of patients (215/221) with chronic PAD, whereas the rate of run-off CTA with non-diagnostic image quality was considerably higher in the calf and foot level (acute vs. chronic; calf: 28% vs.17%; foot: 52% vs. 20%). Reliability of treatment decision was superior for patients with chronic (123/133 = 92%) than for patients with acute PAD (64/78 = 82%, P = 0.02).

Conclusion

Run-off CTA is a reliable imaging modality for primary diag-nostic work-up of patients with acute and chronic PAD.

Standardization of administered activities in pediatric nuclear medicine: a report of the first nuclear medicine global initiative project, part 1-statement of the issue and a review of available resources

The Nuclear Medicine Global Initiative (NMGI) was formed in 2012 and consists of 13 international organizations with direct involvement in nuclear medicine. The underlying objectives of the NMGI were to promote human health by advancing the field of nuclear medicine and molecular imaging, encourage global collaboration in education, and harmonize procedure guidelines and other policies that ultimately lead to improvements in quality and safety in the field throughout the world. For its first project, the NMGI decided to consider the issues involved in the standardization of administered activities in pediatric nuclear medicine. This article presents part 1 of the final report of this initial project of the NMGI. It provides a review of the value of pediatric nuclear medicine, the current understanding of the carcinogenic risk of radiation as it pertains to the administration of radiopharmaceuticals in children, and the application of dosimetric models in children. A listing of pertinent educational and reference resources available in print and online is also provided. The forthcoming part 2 report will discuss current standards for administered activities in children and adolescents that have been developed by various organizations and an evaluation of the current practice of pediatric nuclear medicine specifically with regard to administered activities as determined by an international survey of nuclear medicine clinics and centers. Lastly, the part 2 report will recommend a path forward toward global standardization of the administration of radiopharmaceuticals in children.

Evaluation of a chest circumference-adapted protocol for low-dose 128-slice coronary CT angiography with prospective electrocardiogram triggering

Objective

To assess the effect of chest circumference-adapted scanning protocol on radiation exposure and image quality in patients undergoing prospective electrocardiogram (ECG)-triggered coronary CT angiography (CCTA).

Materials and Methods

One hundred-eighty-five consecutive patients, who had undergone prospective ECG triggering CCTA with a 128-slice CT, were included in the present study. Nipple-level chest circumference, body weight and height were measured before CT examinations. Patients were divided into four groups based on kV/ref·mAs = 100/200, 100/250, 120/200, and 120/250, when patient's chest circumference was ≤ 85.0 (n = 56), 85.0-90.0 (n = 53), 90.0-95.0 (n = 44), and > 95.0 (n = 32), respectively. Image quality per-segment was independently assessed by two experienced observers. Image noise and attenuation were also measured. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. The effective radiation dose was calculated using CT dose volume index and the dose-length product.

Results

A significant correlation was observed between patients' chest circumference and body mass index (r = 0.762, p < 0.001). Chest circumference ranged from 74 to 105 cm, and the mean effective radiation dose was 1.9-3.8 mSv. Diagnostic image quality was obtained in 98.5% (2440/2478) of all evaluated coronary segments without any significant differences among the four groups (p = 0.650). No significant difference in image noise was observed among the four groups (p = 0.439), thus supporting the validity of the chest circumference-adapted scanning protocol. However, vessel attenuation, SNR and CNR were significantly higher in the 100 kV groups than in the 120 kV groups (p < 0.05).

Conclusion

A measure of chest circumference can be used to adapt tube voltage and current for individualized radiation dose control, with resultant similar image noise and sustained diagnostic image quality.

Internal dose assessment of (-)-18F-flubatine, comparing animal model datasets of mice and piglets with first-in-human results

(-)-(18)F-flubatine is a promising tracer for neuroimaging of nicotinic acetylcholine receptors (nAChRs), subtype α4β2, using PET. Radiation doses after intravenous administration of the tracer in mice and piglets were assessed to determine the organ doses (ODs) and the effective dose (ED) to humans. The results were compared with subsequent clinical investigations in human volunteers.

METHODS

Twenty-seven female CD1 mice (weight ± SD, 28.2 ± 2.1 g) received intravenous injection of 0.75 ± 0.33 MBq of (-)-(18)F-flubatine. Up to 240 min after injection, 3 animals per time point were sacrificed and the organs harvested, weighed, and counted in a γ counter to determine mass and activity, respectively. Furthermore, whole-body PET scans of 5 female piglets (age ± SD, 44 ± 3 d; weight ± SD, 13.7 ± 1.7 kg) and 3 humans (2 men and 1 woman; age ± SD, 59.6 ± 3.9 y; weight ± SD, 74.3 ± 3.1 kg) were obtained up to 236 min (piglets) and 355 min (humans) after injection of 186.6 ± 7.4 and 353.7 ± 10.2 MBq of (-)-(18)F-flubatine, respectively, using a PET/CT scanner. The CT was used for delineation of the organs. Exponential curves were fitted to the time-activity-data, and time and mass scales were adapted to the human anatomy. The ODs were calculated using OLINDA/EXM (version 1.0); EDs were calculated with the tissue-weighting factors of ICRP103.

RESULTS

After the injection of (-)-(18)F-flubatine, there were no adverse or clinically detectable pharmacologic effects in any of the subjects. The highest activities after injection were found in the kidneys, urinary bladder, and liver. The urinary bladder receives the highest OD in all investigated species, followed by the kidneys and the liver for animals and humans, respectively. On the basis of mouse, piglet, and human kinetic data, the projected human ED of (-)-(18)F-flubatine was estimated to be 12.5 μSv/MBq in mice, 14.7 ± 0.7 μSv/MBq in piglets, and 23.4 ± 0.4 μSv/MBq in humans.

CONCLUSION

As has been demonstrated for other PET radiotracers, preclinical (i.e., animal-derived) dosimetry underestimates the ED to humans, in the current case of (-)-(18)F-flubatine by 34%-44%.

Evaluation of organ doses and effective dose according to the ICRP Publication 110 reference male/female phantom and the modified ImPACT CT patient dosimetry

We modified the Imaging Performance Assessment of CT scanners (ImPACT) to evaluate the organ doses and the effective dose based on the International Commission on Radiological Protection (ICRP) Publication 110 reference male/female phantom with the Aquilion ONE ViSION Edition scanner. To select the new CT scanner, the measurement results of the CTDI100,c and CTDI100,p for the 160 (head) and the 320 (body) mm polymethylmethacrylate phantoms, respectively, were entered on the Excel worksheet. To compute the organ doses and effective dose of the ICRP reference male/female phantom, the conversion factors obtained by comparison between the organ doses of different types of phantom were applied. The organ doses and the effective dose were almost identical for the ICRP reference male/female and modified ImPACT. The results of this study showed that, with the dose assessment of the ImPACT, the difference in sex influences only testes and ovaries. Because the MIRD-5 phantom represents a partially hermaphrodite adult, the phantom has the dimensions of the male reference man including testes, ovaries, and uterus but no female breasts, whereas the ICRP male/female phantom includes whole-body male and female anatomies based on high-resolution anatomical datasets. The conversion factors can be used to estimate the doses of a male and a female accurately, and efficient dose assessment can be performed with the modified ImPACT.

What is the preferred strength setting of the sinogram-affirmed iterative reconstruction algorithm in abdominal CT imaging?

Our primary objective in this study was to determine the preferred strength setting for the sinogram-affirmed iterative reconstruction algorithm (SAFIRE) in abdominal computed tomography (CT) imaging. Sixteen consecutive clinical CT scans of the abdomen were reconstructed by use of traditional filtered back projection (FBP) and 5 SAFIRE strengths: S1-S5. Six readers of differing experience were asked to rank the images on preference for overall diagnostic quality. The contrast-to-noise ratio was not significantly different between SAFIRE S1 and FBP, but increased with increasing SAFIRE strength. For pooled data, S2 and S3 were preferred equally but both were preferred over all other reconstructions. S5 was the least preferred, with FBP the next least preferred. This represents a marked disparity between the image quality based on quantitative parameters and qualitative preference. Care should be taken to factor in qualitative in addition to quantitative aspects of image quality when one is optimizing iterative reconstruction images.

Automatic detection and quantification of the Agatston coronary artery calcium score on contrast computed tomography angiography

Potentially, Agatston coronary artery calcium (CAC) score could be calculated on contrast computed tomography coronary angiography (CTA). This will make a separate non-contrast CT scan superfluous. This study aims to assess the performance of a novel fully automatic algorithm to detect and quantify the Agatston CAC score in contrast CTA images. From a clinical registry, 20 patients were randomly selected for each CAC category (i.e. 0, 1-99, 100-399, 400-999, ≥1,000). The Agatston CAC score on non-contrast CT was calculated manually, while the novel algorithm was used to automatically detect and quantify Agatston CAC score in contrast CTA images. The resulting Agatston CAC scores were validated against the non-contrast images. A total of 100 patients (60 ± 11 years, 63 men) were included. The median CAC score on non-contrast CT was 145 (IQR 5-760), whereas the contrast CTA CAC score was 170 (IQR 23-594) (P = 0.004). The automatically computed CAC score showed a high correlation (R = 0.949; P < 0.001) and intra-class correlation (R = 0.863; P < 0.001) with non-contrast CT CAC score. Moreover, agreement within CAC categories was good (κ 0.588). Fully automatic detection of Agatston CAC score on contrast CTA is feasible and showed high correlation with non-contrast CT CAC score. This could imply a radiation dose reduction and time saving by omitting the non-contrast scan.

Fetal and maternal absorbed dose estimates for positron-emitting molecular imaging probes

PET and hybrid (PET/CT and PET/MR) imaging currently play a pivotal role in clinical diagnosis, staging and restaging, treatment, and surveillance of several diseases. As such, limiting the radiation exposure of special patients, such as pregnant women, from PET procedures is an important challenge that needs to be appropriately addressed because of the high sensitivity of the developing embryo/fetus to ionizing radiation. Therefore, accurate radiation dose calculation for the embryo/fetus and pregnant patient from common positron-emitting radiotracers is highly desired.

METHODS

To obtain representative estimates of radiation dose to the human body, realistic biologic and physical models should be used. In this work, we evaluate the S values of 9 positron-emitting radionuclides ((11)C, (13)N, (15)O, (18)F, (64)Cu, (68)Ga, (82)Rb, (86)Y, and (124)I) and the absorbed and effective doses for 21 positron-emitting labeled radiotracers using realistic anthropomorphic computational phantoms of early pregnancy and at 3-, 6-, and 9-mo of gestation and the most recent biokinetic data available. The Monte Carlo N-Particle eXtended general-purpose Monte Carlo code was used for radiation transport simulation.

RESULTS

The absorbed dose to the pregnant model is less influenced by the gestation for most organs or tissues, but the anatomic changes of the maternal body increases the effective dose for some radiotracers. For (18)F-FDG, the estimated absorbed doses to the embryo/fetus are 3.05E-02, 2.27E-02, 1.50E-02, and 1.33E-02 mGy/MBq at early pregnancy and 3-, 6-, and 9-mo gestation, respectively. The absorbed dose is nonuniformly distributed in the fetus and would be 1.03-2 times higher in the fetal brain than in other fetal soft tissues.

CONCLUSION

The generated S values can be exploited to estimate the radiation dose delivered to pregnant patients and the embryo/fetus from various PET radiotracers used in clinical and research settings. The generated dosimetric database of radiotracers using new-generation computational models can be used for the assessment of radiation risks to pregnant women and the embryo/fetus undergoing PET/CT imaging procedures. This work also contributes to a better understanding of the absorbed dose distribution in the fetus.

Comparison of image quality, myocardial perfusion, and left ventricular function between standard imaging and single-injection ultra-low-dose imaging using a high-efficiency SPECT camera: the MILLISIEVERT study

SPECT myocardial perfusion imaging plays a central role in coronary artery disease diagnosis, but concerns exist regarding its radiation burden. Compared with standard Anger SPECT (A-SPECT) cameras, new high-efficiency (HE) cameras with specialized collimators and solid-state cadmium-zinc-telluride detectors offer potential to maintain image quality (IQ), while reducing administered activity and thus radiation dose to patients. No previous study has compared IQ, interpretation, total perfusion deficit (TPD), or ejection fraction (EF) in patients receiving both ultra-low-dose (ULD) imaging on an HE SPECT camera and standard low-dose (SLD) A-SPECT imaging.

METHODS

We compared ULD HE SPECT with SLD A-SPECT imaging by dividing the rest dose in 101 patients at 3 sites scheduled to undergo clinical A-SPECT myocardial perfusion imaging using a same day rest-stress (99m)Tc protocol. Patients underwent HE SPECT imaging after an initial approximately 130-MBq (3.5 mCi) dose and SLD-A-SPECT imaging after the remainder of the planned dose. Images were scored visually by 2 masked readers for IQ and summed rest score. TPD and EF were assessed quantitatively.

RESULTS

Mean activity was 134 MBq (3.62 mCi) for ULD HE SPECT (effective dose, 1.15 mSv) and 278 MBq (7.50 mCi, 2.39 mSv) for SLD A-SPECT. Overall IQ was superior for ULD HE SPECT (P < 0.0001), with twice as many studies graded excellent quality. Extracardiac activity and overall perfusion assessment were similar. Between-method correlations were high for summed rest score (r = 0.87), TPD (r = 0.91), and EF (r = 0.88).

CONCLUSION

ULD HE SPECT rest imaging correlates highly with SLD A-SPECT. It has improved image quality, comparable extracardiac activity, and achieves radiation dose reduction to 1 mSv for a single injection.

The evolution and investigation of native coronary arteries in patients after coronary stent implantation: a study by 320-detector CT angiography

To study the role of 320-detector coronary computed tomography angiography (CTA) in assessing native coronary arteries in patients treated with coronary stents. 123 patients with coronary stenting received both CTA and conventional coronary angiography (CCA) within 1 day. The clinical parameters, coronary calcium scoring, CTA and CCA were analyzed to determine the prevalence of significant stenosis of native coronary arteries (SSNCA), the predictive value of CTA and the factors correlating with SSNCA and newly developed SSNCA after stenting (NDSSNCAS), with CCA as the standard of reference, using both vessel-based analysis (VBA) and patient-based analysis (PBA). Both the source and the reconstructed images were analyzed by CTA. All native coronary arteries were interpretable independent of cardiac motion. CTA showed a sensitivity/specificity of 93.5%/97.3% and 92.5%/92.5% in diagnosing SSNCA in VBA and PBA, respectively. The significant factors related to SSNCA were higher calcium scores (P = 0.003), a higher serum glucose level (P = 0.048), a greater number of vessels without previous stent placement (P = 0.003) and fewer stents implanted within the vessels (P = 0.003). The risk factors showed no significant correlation from PBA on SSNCA or from NDSSNCAS on either VBA or PBA. CTA demonstrates excellent correlation with CCA. The prevalence of SSNCA is significantly correlated with the presence of higher calcium scores in the arteries, a higher serum glucose level, a greater number of vessels without previous stent placement and fewer stents implanted within the vessels; PBA on SSNCA and NDSSNCAS on both VBA and PBA showed no significance.

Radial differential interior tomography and its image reconstruction with differentiated backprojection and projection onto convex sets

PURPOSE

Interior tomography has been recognized as one of the most effective approaches in computed tomography (CT) to reduce radiation dose rendered to patients. In this work, the authors propose and evaluate an imaging method of radial differential interior tomography.

METHODS

In interior tomography, an x-ray beam is collimated to only irradiate the region of interest (ROI) with suspected lesions while the surrounding area∕volume of normal tissues∕organs is spared. In the proposed imaging method of radial differential interior tomography, the outcome is a ROI image that has gone through a radial differential filtering. The image reconstruction algorithm for the radial differential interior tomography is kept in the fashion of differentiated backprojection and projection onto convex sets, but the required a priori knowledge in a small round area becomes zero and may be more readily available in practice.

RESULTS

Using the projection data simulated by computer and acquired by CT scanner, the authors evaluate and verify the performance of the proposed radial differential interior tomography method and its associated image reconstruction algorithm. The preliminary results show that the proposed imaging method can generate an image that is the radial differentiation of a conventional tomographic image and is robust over noise that inevitably exist in practice.

CONCLUSIONS

It is believed that the proposed imaging method may find its utility in advanced clinical applications wherein a ROI-based image processing and analysis is required for lesion visualization, characterization, and diagnosis.