A Primer on Computed Tomography Perfusion Imaging for the Emergency Physician

BACKGROUND

Brain noncontrast computed tomography (CT), CT angiography, and magnetic resonance imaging have been used clinically for decades, and emergency physicians have a good understanding of their indications, the meaning of their results, and some facility with the interpretation of CT. However, brain CT perfusion (CTP) is relatively new and emergency physicians are less familiar with its basic concepts, indications, and role in managing patients with neurological emergencies.

OBJECTIVE

We will review the parameters of clinical interest on a CTP report, and how to incorporate them into clinical decision-making.

DISCUSSION

Endovascular therapies paired with CTP have opened up a new frontier in stroke management for severely debilitated stroke patients. It is important for emergency physicians to have an understanding of CTP and how to use it clinically.

CONCLUSION

Taking care of patients with large-vessel occlusions is multidisciplinary, and emergency physicians need to understand CTP imaging and its clinical utility.

Size-Specific Dose Estimates Based on Water-Equivalent Diameter and Effective Diameter in Computed Tomography Coronary Angiography

BACKGROUND To determine the difference in size-specific dose estimates (SSDEs), separately based on effective diameter (deff) and water equivalent diameter (dw) of the central slice of the scan range in computed tomography coronary angiography (CTCA). MATERIAL AND METHODS There were 134 patients who underwent CTCA examination, were electronically retrieved. SSDEs (SSDEdeff and SSDEdw) were calculated using 2 approaches: deff and dw. The median SSDEs and mean absolute relative difference of SSDEs were calculated. Linear regression model was used to assess the absolute relative difference of SSDEs based on the ratio of deff to dw. RESULTS The median values of SSDEdeff and SSDEdw were 18.26 mGy and 20.56 mGy, respectively (P<0.01). The former was about 10.08% smaller than the latter. The mean absolute relative difference of SSDEs was 10.48%, ranging from 0.33% to 24.16%. A considerably positive correlation was found between the absolute relative difference of SSDEs and the ratio of deff to dw (R²=0.9561, r=0.979, P<0.01). CONCLUSIONS The value of SSDEdeff was smaller by an average of about 10.08% than SSDEdw in CTCA, and the absolute relative difference increased linearly with the ratio of effective diameter to water equivalent diameter.

3D imaging and stealth navigation instead of CT guidance for radiofrequency ablation of osteoid osteomas: a series of 52 patients

Background

Osteoid osteomas are benign bone neoplasms that may cause severe pain and limit function. They are commonly treated by radiofrequency ablation (RFA) through a needle inserted into the nidus of the lesion under CT guidance, which is associated with exposure of young patients to relatively high dose of radiation. The objective of this study was to investigate the amount of radiation, effectiveness and safety of an alternative imaging approach, the 3D image-guided (O-arm) technology and the Stealth navigation.

Methods

We retrospectively reviewed 52 electronic medical files of patients (mean age 24.7 years, range 8–59 years) who were treated with thermal ablation of benign osteoid osteomas guided by the navigated O-arm-assisted technique in our institution between 2015 and 2017. Data were extracted on the associated complications, the reduction in pain at 3 months and one year postoperatively, and the amount of radiation administered during the procedure.

Results

The level of pain on a visual analogue scale decreased from the preoperative average of 7.73 to 0 at the 3-month follow-up. The mean dose-length product was 544.7 mGycm² compared to the reported radiation exposure of 1971–7946 mGycm² of CT-guided radio ablations. The one intra-operative complication was a superficial burn in the subcutaneous lesion in a tibia that was treated locally with no major influence on recovery.

Conclusions

RFA ablation guided by 3D O-arm stealth navigation is as effective as the traditional CT-guided technique with the advantage of lower radiation exposure.

Trial registration

Retrospective study number 0388–17-TLV at Tel Aviv Sourasky Medical Center IRB, approved at 25.10.17.

EFFECTS OF THE SCAN RANGE ON RADIATION DOSE IN THE COMPUTED TOMOGRAPHY COMPONENT OF ONCOLOGY POSITRON EMISSION TOMOGRAPHY/COMPUTED TOMOGRAPHY

We performed phantom experiments to investigate radiation dose in the computed tomography component of oncology positron emission tomography/computed tomography in relation to the scan range. Computed tomography images of an anthropomorphic whole-body phantom were obtained from the head top to the feet, from the head top to the proximal thigh or from the skull base to the proximal thigh. Automatic exposure control using the posteroanterior and lateral scout images offered reasonable tube current modulation corresponding to the body thickness. However, when the posteroanterior scout alone was used, unexpectedly high current was applied in the head and upper chest. When effective dose was calculated on a region-by-region basis, it did not differ greatly irrespective of the scan range. In contrary, when effective dose was estimated simply by multiplying the scanner-derived dose-length product by a single conversion factor, estimates increased definitely with the scan range, indicating severe overestimation in whole-body imaging.

Diagnostic reference levels for paediatric CT in Jordan

This study aimed to investigate the current status of Diagnostic Reference Levels (DRLs) in paediatric CT across Jordan. The dose data for four main CT examinations (brain, chest, abdominopelvic, and chest, abdomen and pelvis (CAP)) in hospitals and imaging centres (n = 4) were measured. The volume CT dose index (CTDIvol) and Dose Length Product (DLP) values were compared within the different hospitals and age groups (<1 year, 1-4 years, 5-10 years and 11-18 years). DRLs in Jordan were compared to international DRLs. The paediatric population consisted of 1818 children; 61.4% of them were male. There were significant variations between the DRLs for each CT scanner with an up to four-fold difference in dose between hospitals. There were apparent significant differences between Jordan and other countries with the DLPs in Jordan being relatively high. However, for CTDIvol, the values in Jordan were close to those of other countries. This study confirmed variations in the CTDIvol and DLP values of paediatric CT scans in Jordan. These variations were attributed to the different protocols and equipment used. There is a need to optimise paediatric CT examinations doses in Jordan.

Computed Tomography Radiation Exposure Among Referred Kidney Stone Patients: Results from the Registry for Stones of the Kidney and Ureter

Purpose: Kidney stone patients routinely have CT scans during diagnostic work-up before being referred to a tertiary center. How often these patients exceed the recommended dose limits for occupational radiation exposure of >100 mSv for 5 years and >50 mSv in a single year from CT alone remains unknown. This study aimed to quantify radiation doses from CTs received by stone patients before their evaluation at a tertiary care stone clinic. Methods: From November 2015 to March 2017, consecutive new patients enrolled into the Registry for Stones of the Kidney and Ureter (ReSKU™) had the dose-length product of every available CT abdomen/pelvis within 5 years of their initial visit recorded, allowing for an effective dose (EDose) calculation. Multivariate logistic regression analysis identified factors associated with exceeding recommended dose limits. Models were created to test radiation reducing effects of low-dose and phase-reduction CT protocols. Results: Of 343 noncontrast CTs performed, only 29 (8%) were low-dose CTs (calculated EDose <4 mSv). Among 389 total patients, 101 (26%) and 25 (6%) had an EDose >20 mSv and >50 mSv/year, respectively. Increased body mass index, number of scans, and multiphase scans were associated with exceeding exposure thresholds (p < 0.01). The implementation of a low-dose CT protocol decreased the estimated number of scans contributing to overexposure by >50%. Conclusions: Stone patients referred to a tertiary stone center may receive excessive radiation from CT scans alone. Unnecessary phases and underutilization of low-dose CT protocols continue to take place. Enacting new approaches to CT protocols may spare stone patients from exceeding recommended dose limits.

Assessment of iterative image reconstruction on kidney and liver donors: Potential role of adaptive iterative dose reduction 3D (AIDR 3D) technology

OBJECTIVE

The aim of this study was to evaluate the radiation exposure levels in two different types of subjects including liver and kidney donors in diagnostic assessment of transplant operation and also the significance of dose reduction on total effective dose.

MATERIALS AND METHODS

A number of Sixty subjects (40 males and 20 females, average age of 35 ± 10 years) were randomly prospectively recruited and equally divided into two distinct groups namely kidney donors (KD, 24 M and 6 F) and liver donors (LD, 21 M and 9 female). Kidney donors were divided into full dose (KFD, n = 20) group and low dose (KLD, n = 10) group. They had undergone dynamic renal scan using Tc99 m-DTPA, CT renal angiography and x-ray plain radiograph. Liver donors were divided into full dose (LFD, n = 20) and low dose (LLD, n = 10) groups and performed CT liver volumetry. The CT dose index (CTDIvol), dose length product (DLP), total milli-ampere product time mAs, effective dose and image noise index were measured in all subjects of kidney and liver donors comparing full dose and low dose protocols.

RESULTS

In comparison of all subjects of kidney donor groups (KFD vs KLD), the parameters (mAs = 16386.8 ± 3140.7 vs 2830.286 ± 831.676), (CTDIvol = 183.19 ± 32.58 mGy vs. 45.5 ± 13.3 mGy), DLP = 2884 ± 859.0 mGy.cm vs. 1437.5 ± 399 mGy.cm) and (effective dose = 49.0 ± 9.0 mSv vs. 18.9 mSv±5.7 mSv) were significant, p < 0.0005. Statistical evaluation of liver donors groups (LFD vs LLD) showed that (mAs = 14348.8 ± 4571.8 vs 3123.357 ± 794.5), (CTDIvol = 333.6 ± 59.5 mGy vs. 51.4 ± 13 mGy), (DLP = 3268.3 ± 604.3 mGy.cm vs 1260.5 ± 404.6 mGy.cm) and (effective dose = 43.3 mSv±12.9 mSv vs. 21.6 ± 5.9 mSv) are statistically significant, p < 0.0005. Nevertheless, the comparative evaluation of the image quality noise index of KFD vs KLD groups and LFD vs LLD showed a no statistical significance p > 0.05.

CONCLUSION

Renal and liver donors bear a relatively significant radiation dose due to diagnostic evaluation and patient management. The CT iterative reconstruction using AIDR3D proved very valuable tool in dose reduction such that it can reduce 37% in kidney donors and 48% in liver donors while able to maintain an acceptable image quality. Monitoring of those subjects on the clinical and radiobiological levels are recommended.

Tailoring CT Dose to Patient Size: Implementation of the Updated 2017 ACR Size-specific Diagnostic Reference Levels

RATIONALE AND OBJECTIVES

To use an automatic computed tomography (CT) dose monitoring system to analyze the institutional chest and abdominopelvic CT dose data as regards the updated 2017 American College of Radiology (ACR) diagnostic reference levels (DRLs) based on water-equivalent diameter (Dw) and size-specific dose estimates (SSDE) to detect patient-size subgroups in which CT dose can be optimized.

MATERIALS AND METHODS

All chest CT examinations performed between July 2016 and April 2017 with and without contrast material, CT of the pulmonary arteries, and abdominopelvic CT with and without contrast material were included in this retrospective study. Dw and SSDE were automatically calculated for all scans using a previously validated in-house developed Matlab software and stored into our CT dose monitoring system. CT dose data were analyzed as regards the updated ACR DRLs (size groups: 21-25 cm, 25-29 cm, 29-33 cm, 33-37 cm, 37-41 cm). SSDE and volumetric computed tomography dose index (CTDIvol) were used as CT dose parameter.

RESULTS

Overall, 30,002 CT examinations were performed in the study period, 3860 of which were included in the analysis (mean age 62.1 ± 16.4 years, Dw 29.0 ± 3.3 cm; n = 577 chest CT without contrast material, n = 628 chest CT with contrast material, n = 346 CT of chest pulmonary, n = 563 abdominopelvic CT without contrast material, n = 1746 abdominopelvic CT with contrast material). Mean SSDE and CTDIvol relative to the updated DRLs were 43.3 ± 26.4 and 45.1 ± 27.9% for noncontrast chest CT, 52.3 ± 23.1 and 52.0 ± 23.1% for contrast-enhanced chest CT, 68.8 ± 29.5 and 70.0 ± 31.0% for CT of pulmonary arteries, 41.9 ± 29.2 and 43.3 ± 31.3% for noncontrast abdominopelvic CT, and 56.8 ± 22.2 and 58.8 ± 24.4% for contrast-enhanced abdominopelvic CT. Lowest dose compared to the DRLs was found for the Dw group of 21-25 cm in noncontrast abdominopelvic CT (SSDE 30.4 ± 21.8%, CTDIvol 30.8 ± 21.4%). Solely the group of patients with a Dw of 37-41 cm undergoing noncontrast abdominopelvic CT exceeded the ACR DRL (SSDE 100.3 ± 59.0%, CTDIvol 107.1 ± 63.5%).

CONCLUSIONS

On average, mean SSDE and CTDIvol of our institutional chest and abdominopelvic CT protocols were lower than the updated 2017 ACR DRLs. Size-specific subgroup analysis revealed a wide variability of SSDE and CTDIvol across CT protocols and patient size groups with a transgression of DRLs in noncontrast abdominopelvic CT of large patients (Dw 37-41 cm).

Multiphase acquisitions in pediatric abdominal-pelvic CT are a common practice and contribute to unnecessary radiation dose

BACKGROUND

Many patients at our pediatric hospital have had a contrast-enhanced CT of the abdomen and pelvis performed by an outside imaging facility before admission. We have noticed that many of these exams are multiphase, which may contribute to unnecessary radiation dose.

OBJECTIVE

To determine the frequency of multiphase acquisitions and radiation dose indices in contrast-enhanced CTs of the abdomen and pelvis performed by outside imaging facilities in patients who were subsequently transferred to our pediatric hospital for care, and compare these metrics to contrast-enhanced CTs of the abdomen and pelvis performed internally.

MATERIALS AND METHODS

A retrospective analysis was performed of contrast-enhanced CTs of the abdomen and pelvis from outside imaging facilities uploaded to our picture archiving and communication system (PACS) between January 1, 2012, and December 31, 2015. CT images and dose pages were reviewed to determine the number of phases and dose indices (CT dose index-volume [CTDI_vol], dose-length product, size-specific dose estimate). Exams for abdominal or pelvic mass, trauma or urinary leak indications were excluded. Data were compared to internally acquired contrast-enhanced CTs of the abdomen and pelvis by querying the American College of Radiology (ACR) Dose Index Registry. This review was institutional review board and HIPAA compliant.

RESULTS

There were 754 contrast-enhanced CTs of the abdomen and pelvis from 104 outside imaging facilities. Fifty-three percent (399/754) had 2 phases, and 2% (14/754) had 3 or more phases. Of the 939 contrast-enhanced CTs of the abdomen and pelvis performed internally, 12% (115) were multiphase exams. Of 88% (664) contrast-enhanced CTs of the abdomen and pelvis from outside imaging facilities with dose data, CTDI_vol was 2.7 times higher than our institution contrast-enhanced CTs of the abdomen and pelvis (939) for all age categories as defined by the ACR Dose Index Registry (mean: 9.4 vs. 3.5 mGy, P<0.0001). The majority (74%) of multiphase exams were performed by 9 of 104 outside imaging facilities.

CONCLUSION

Multiphase acquisitions in routine contrast-enhanced CT of the abdomen and pelvis exams at outside imaging facilities are more frequent than those at a dedicated pediatric institution and contribute to unnecessary radiation dose. A contrast-enhanced CT of the abdomen and pelvis exam from an outside imaging facility with two passes may have as much as four times to six times the dose as the same exam performed with a single pass at a pediatric imaging center. We advocate for imaging facilities with high multiphase rates to eliminate multiple phases from routine contrast-enhanced CT of the abdomen and pelvis exams in children.

Examination of Pediatric Radiation Dose Delivered After Cervical Spine Trauma

OBJECTIVES

Pediatric cervical spine injuries (CSIs) are rare but potentially fatal injuries. Plain radiographs (x-rays) and computed tomography (CT) are used to diagnose CSIs. Given concerns related to radiation exposure, the utility of x-rays in diagnosing CSIs compared with other forms of imaging must be examined.

METHODS

Patients younger than 19 years presenting with possible CSI to an urban tertiary care hospital who received imaging for possible CSI between January 1, 2011, and December 31, 2013, were included. The dose-length product was abstracted from the PACS system. Test performance for x-ray, CT, and MRI were calculated and effective radiation dose by age group was analyzed using the Kruskal-Wallis Test.

RESULTS

A total of 671 patient charts were reviewed, 574 children were included in the study cohort. Median age of enrolled children was 9.70 (interquartile range, 4.78-13.83) years; 42.5% were female. Test performance of x-ray, CT, and MRI to detect CSI were calculated. Cervical x-rays performed only slightly inferior to CT. Sensitivity was 83% (95% confidence interval [CI], 36-99%), and specificity was 97% (95% CI, 96%-99%) versus 100% (95% CI, 96%-100%) for CT. Median effective dose of radiation for cervical CTs was 4.51 mSv (interquartile range, 3.84-5.59 mSv). Median dose significantly increased with age (2.94-5.10 mSv, P < 0.001).

CONCLUSIONS

Plain radiographs were largely sufficient to screen for CSIs, indicating their utility as a screening tool for CSIs. The incidence of CSIs in our sample was similar to prior reports. The effective radiation dose delivered during pediatric head and cervical CTs were lower than previously published estimates.

IPEM topical report: the first UK survey of dose indices from radiotherapy treatment planning computed tomography scans for adult patients

CT scans are an integral component of modern radiotherapy treatments, enabling the accurate localisation of the treatment target and organs-at-risk, and providing the tissue density information required for the calculation of dose in the treatment planning system. For these reasons, it is important to ensure exposures are optimised to give the required clinical image quality with doses that are as low as reasonably achievable. However, there is little guidance in the literature on dose levels in radiotherapy CT imaging either within the UK or internationally. This IPEM topical report presents the results of the first UK wide survey of dose indices in radiotherapy CT planning scans. Patient dose indices were collected for prostate, gynaecological, breast, lung 3D, lung 4D, brain and head and neck scans. Median values per scanner and examination type were calculated and national dose reference levels and 'achievable levels' of CT dose index (CTDI_vol), dose-length-product (DLP) and scan length are proposed based on the third quartile and median values of these distributions, respectively. A total of 68 radiotherapy CT scanners were included in this audit. The proposed dose reference levels for CTDI_vol and DLP are; prostate 16 mGy and 570 mGy · cm, gynaecological 16 mGy and 610 mGy · cm, breast 10 mGy and 390 mGy · cm, lung 3D 14 mGy and 550 mGy · cm, lung 4D 63 mGy and 1750 mGy · cm, brain 50 mGy and 1500 mGy · cm and head and neck 49 mGy and 2150 mGy · cm. Significant variations in dose indices were noted, with head and neck and lung 4D yielding a factor of eighteen difference between the lowest and highest dose scanners. There was also evidence of some clustering in the data by scanner manufacturer, which may be indicative of a lack of local optimisation of individual systems to the clinical task. It is anticipated that providing this data to the UK and wider radiotherapy community will aid the optimisation of treatment planning CT scan protocols.

Comparison of methods to estimate water-equivalent diameter for calculation of patient dose

Modern CT systems seek to evaluate patient-specific dose by converting the CT dose index generated during a procedure to a size-specific dose estimate using conversion factors that are related to patient attenuation properties. The most accurate way to measure patient attenuation is to evaluate a full-field-of-view reconstruction of the whole scan length and calculating the true water-equivalent diameter (Dw ) using CT numbers; however, due to time constraints, less accurate methods to estimate Dw using patient geometry measurements are used more widely. In this study we compared the accuracy of Dw values calculated from three different methods across 35 sample scans and compared them to the true Dw . These three estimation methods were: measurement of patient lateral dimension from a pre-scan localizer radiograph; measurement of the sum of anteroposterior and lateral dimensions from a reconstructed central slice; and using CT numbers from a central slice only. Using the localizer geometry method, 22 out of 35 (62%) samples estimated Dw within 20% of the true value. The middle slice attenuation and geometry methods gave estimations within the 20% margin for all 35 samples.

Operator radiation doses during CT-guided spine procedures

OBJECTIVES

To perform a pilot study to quantify the radiation dose incident on operators during CT-guided interventional spine procedures, and provide a quick method to approximate it based on the total amount of radiation reported by the CT scanner.

PATIENTS AND METHODS

Data retrospectively obtained from 26 consecutive CT-guided spine procedures, encompassing a variety of interventions. Intermittent low-dose limited-coverage CT-scanning performed using a "step and shoot" mode to visualize needle advancement. The operator wore an electronic direct dosimeter to record the dose measured above the operator's lead apron [μGy] for each procedure. Total amount of radiation used for CT-guidance quantified by the Dose-Length Product (DLP) [mGy-cm] provided by the CT scanner. The relationship between the operator's dose and the DLP was assessed.

RESULTS

Average and median operator's dose were 2.3 and 1.9 μGy, respectively, with half of these values ranging between 0.7 and 2.5 μGy. Average and median DLP values used to perform the CT-guided procedure were 58 and 54 mGy-cm respectively, and half of these values ranged between 38 and 68 mGy-cm. There was a statistically significant correlation between the operator's dose and the DLP used to perform CT-guidance (r = 0.61), with an operator's dose-DLP conversion factor of 0.04 μGy / 1 mGy-cm (range: 0.006-0.083 μGy / 1 mGy-cm).

CONCLUSIONS

In our series, the average amount of radiation used during CT guided procedures was about 50 mGy-cm (DLP), and the corresponding average operator's dose was about 2 μGy. We showed how an approximate estimate of the operator's dose could be obtained right after each procedure, based on the CT-scanner DLP output.

Diagnostic reference levels for common computed tomography (CT) examinations: results from the first Nigerian nationwide dose survey

PURPOSE

To explore doses from common adult computed tomography (CT) examinations and propose national diagnostic reference levels (nDRLs) for Nigeria.

MATERIALS AND METHODS

This retrospective study was approved by the Nnamdi Azikiwe University and University Teaching Hospital Institutional Review Boards (IRB: NAUTH/CS/66/Vol8/84) and involved dose surveys of adult CT examinations across the six geographical regions of Nigeria and Abuja from January 2016 to August 2017. Dose data of adult head, chest and abdomen/pelvis CT examinations were extracted from patient folders. The median, 75th and 25th percentile CT dose index volume (CTDI_vol) and dose-length-product (DLP) were computed for each of these procedures. Effective doses (E) for these examinations were estimated using the k conversion factor as described in the ICRP publication 103 (E_DLP = _{k × DLP}).

RESULTS

The proposed 75th percentile CTDI_vol for head, chest, and abdomen/pelvis are 61 mGy, 17 mGy, and 20 mGy, respectively. The corresponding DLPs are 1310 mGy.cm, 735 mGy.cm, and 1486 mGy.cm respectively. The effective doses were 2.75 mSv (head), 10.29 mSv (chest), and 22.29 mSv (abdomen/pelvis).

CONCLUSION

Findings demonstrate wide dose variations within and across centres in Nigeria. The results also show CTDI_vol comparable to international standards, but considerably higher DLP and effective doses.

Dosimetric changes with computed tomography automatic tube-current modulation techniques

The study is aimed at a verification of dose changes for a computed tomography automatic tube-current modulation (ATCM) technique. For this purpose, anthropomorphic phantom and Gafchromic^® XR-QA2 films were used. Radiochromic films were cut according to the shape of two thorax regions. The ATCM algorithm is based on noise index (NI) and three exam protocols with different NI were chosen, of which one was a reference. Results were compared with dose values displayed by the console and with Poisson statistics. The information obtained with radiochromic films has been normalized with respect to the NI reference value to compare dose percentage variations. Results showed that, on average, the information reported by the CT console and calculated values coincide with measurements. The study allowed verification of the dose information reported by the CT console for an ATCM technique. Although this evaluation represents an estimate, the method can be a starting point for further studies.

Radiation dose metrics in multidetector computed tomography examinations: A multicentre retrospective study from seven tertiary care hospitals in Kerala, South India

BACKGROUND

Presently, computed tomography (CT) is the most important source of medical radiation exposure. CT radiation doses vary considerably across institutions depending on the protocol and make of equipment. India does not yet have national or region-specific CT diagnostic reference levels.

AIM

To evaluate radiation doses of consecutive multidetector CT (MDCT) examinations based on anatomic region, performed in 1 month, collected simultaneously from seven tertiary care hospitals in Kerala.

SETTINGS AND DESIGN

Descriptive study.

MATERIALS AND METHODS

We collected the CT radiation dose data of examinations from the seven collaborating tertiary care hospitals in Kerala, performed with MDCT scanners of five different makes. The data included anatomic region, number of phases, CT dose index (CTDIvol), dose-length product (DLP), and effective dose (ED) of each examinations and patient demographic data.

STATISTICAL ANALYSIS

We calculated the 25th, 50th, and 75th percentiles of the CTDIvol, DLP, and ED according to anatomic region. We made descriptive comparisons of these results with corresponding data from other countries.

RESULTS

Of 3553 patients, head was the most frequently performed examination (60%), followed by abdomen (19%). For single-phase head examinations, 75th percentile of CTDIvol was 68.1 mGy, DLP 1120 mGy-cm, and ED 2.1 mSv. The 75th percentiles of CTDIvol, DLP, and ED for single-phase abdomen examinations were 10.6, 509.3, and 7.7, and multiphase examinations were 14.6, 2666.9, and 40.8; single-phase chest examinations were 23.4, 916.7, and 13.38, and multiphase examinations were 19.9, 1737.6, and 25.36; single-phase neck were 24.9, 733.6, and 3.814, and multiphase neck were 24.9, 2076, and 10.79, respectively.

CONCLUSION

This summary CT radiation dose data of most frequently performed anatomical regions could provide a starting point for institutional analysis of CT radiation doses, which in turn leads to meaningful optimization of CT.

Estimation of lifetime attributable risks (LARs) of cancer associated with abdominopelvic radiotherapy treatment planning computed tomography (CT) simulations

PURPOSE

The present study attempts to calculate organ-absorbed and effective doses for cancer patients to estimate the possible cancer induction and cancer mortality risks resulting from 64-slice abdominopelvic computed tomography (CT) simulations for radiotherapy treatment planning (RTTP).

MATERIAL AND METHODS

A group of 70 patients, who underwent 64-slice abdominopelvic CT scan for RTTP, voluntarily participated in the present study. To calculate organ and effective doses in a standard phantom of 70 kg, the collected dosimetric parameters were used with the ImPACT CT Patient Dosimetry Calculator. Patient-specific organ dose and effective dose were calculated by applying related correction factors. For the estimation of lifetime attributable risks (LARs) of cancer incidence and cancer-related mortality, doses in radiosensitive organs were converted to risks based on the data published in Biological Effects of Ionizing Radiation VII (BEIR VII).

RESULTS

The mean ± standard deviation (SD) of the effective dose for males and females were 13.87 ± 2.37 mSv (range: 9.25-18.82 mSv) and 13.04 ± 3.42 mSv (range: 6.99-18.37 mSv), respectively. The mean ± SD of LAR of cancer incidence was 35.34 ± 13.82 cases in males and 34.49 ± 9.63 cases in females per 100,000 persons. The LAR of cancer mortality had the mean ± SD value of 15.38 ± 4.25 and 16.72 ± 3.87 cases per 100,000 persons in males and females respectively.

CONCLUSION

Increase in the LAR of cancer occurrence and mortality due to abdominopelvic treatment planning CT simulation is noticeable and should be considered.

A comparison study of size-specific dose estimate calculation methods

BACKGROUND

The size-specific dose estimate (SSDE) has emerged as an improved metric for use by medical physicists and radiologists for estimating individual patient dose. Several methods of calculating SSDE have been described, ranging from patient thickness or attenuation-based (automated and manual) measurements to weight-based techniques.

OBJECTIVE

To compare the accuracy of thickness vs. weight measurement of body size to allow for the calculation of the size-specific dose estimate (SSDE) in pediatric body CT.

MATERIALS AND METHODS

We retrospectively identified 109 pediatric body CT examinations for SSDE calculation. We examined two automated methods measuring a series of level-specific diameters of the patient's body: method A used the effective diameter and method B used the water-equivalent diameter. Two manual methods measured patient diameter at two predetermined levels: the superior endplate of L2, where body width is typically most thin, and the superior femoral head or iliac crest (for scans that did not include the pelvis), where body width is typically most thick; method C averaged lateral measurements at these two levels from the CT projection scan, and method D averaged lateral and anteroposterior measurements at the same two levels from the axial CT images. Finally, we used body weight to characterize patient size, method E, and compared this with the various other measurement methods. Methods were compared across the entire population as well as by subgroup based on body width.

RESULTS

Concordance correlation (ρ_c) between each of the SSDE calculation methods (methods A-E) was greater than 0.92 across the entire population, although the range was wider when analyzed by subgroup (0.42-0.99). When we compared each SSDE measurement method with CTDI_vol, there was poor correlation, ρ_c<0.77, with percentage differences between 20.8% and 51.0%.

CONCLUSION

Automated computer algorithms are accurate and efficient in the calculation of SSDE. Manual methods based on patient thickness provide acceptable dose estimates for pediatric patients <30 cm in body width. Body weight provides a quick and practical method to identify conversion factors that can be used to estimate SSDE with reasonable accuracy in pediatric patients with body width ≥20 cm.

Evaluation of AAPM Reports 204 and 220: Estimation of effective diameter, water-equivalent diameter, and ellipticity ratios for chest, abdomen, pelvis, and head CT scans

Purpose

To confirm AAPM Reports 204/220 and provide data for the future expansion of these reports by: (a) presenting the first large‐scale confirmation of the reports using clinical data, (b) providing the community with size surrogate data for the head region which was not provided in the original reports, and additionally providing the measurements of patient ellipticity ratio for different body regions.

Method

A total of 884 routine scans were included in our analysis including data from the head, thorax, abdomen, and pelvis for adults and pediatrics. We calculated the ellipticity ratio and all of the size surrogates presented in AAPM Reports 204/220. We correlated the purely geometric‐based metrics with the “gold standard” water‐equivalent diameter (D_W).

Results

Our results and AAPM Reports 204/220 agree within our data's 95% confidence intervals. Outliers to the AAPM reports’ methods were caused by excess gas in the GI tract, exceptionally low BMI, and cranial metaphyseal dysplasia. For the head, we show lower correlation (R² = 0.812) between effective diameter and D_W relative to other body regions. The ellipticity ratio of the shoulder region was the highest at 2.28 ± 0.22 and the head the smallest at 0.85 ± 0.08. The abdomen pelvis, chest, thorax, and abdomen regions all had ellipticity values near 1.5.

Conclusion

We confirmed AAPM reports 204/220 using clinical data and identified patient conditions causing discrepancies. We presented new size surrogate data for the head region and for the first time presented ellipticity data for all regions. Future automatic exposure control characterization should include ellipticity information.

A Study to Determine Whether the Volume-Weighted Computed Tomography Dose Index Gives Reasonable Estimates of Organ Doses for Thai Patients Undergoing Abdomen and Pelvis Computed Tomography Examinations

Introduction:

Values for the CTDI_vol, which is displayed on scanner consoles, give doses relative to a phantom much larger than most Thai patients, and the CTDI_vol does not take account of differences in patient size, which affect organ doses.

Objective:

The purpose of this study was to evaluate relationships for size specific dose estimate (SSDE) and volume weighted computed tomography (CT) dose index (CTDI_vol) with patient size for CT scanners operating under automatic tube current modulation (ATCM).

Methods:

Retrospective data from 244 patients who had undergone abdomen and pelvis examination on GE and Siemens CT scanners were included in this study. The combination of anteroposterior (AP) and lateral dimensions at the level of the first lumbar vertebra (L1) was used to represent patient size. Image noise within the liver was measured, and values of the absorbed dose for organs covered by the primary beam such as the liver, stomach and kidney were calculated using methods described in the literature. Values of CTDI_vol were recorded and SSDE calculated according to the American Association of Physics in Medicine (AAPM) Report No.204. Linear regression models were used to evaluate the relationship between SSDE, CTDI_vol, image noise and patient size.

Results:

SSDE is 20%-50% larger than the CTDI_vol, with values for larger patients being more representative. Both the CTDI_vol and image noise decreased with patient size for Siemens scanners, but the decline in SSDE was less significant. For the GE scanner, the CTDI_vol was a factor of 3-4 lower in small patients compared to larger ones, while the SSDE only decreased by a factor of two. Noise actually decreased slightly with patient size.

Conclusion:

Values of SSDE were similar to the doses calculated for the liver, stomach and kidney, which are covered by the primary beam, confirming that it provides a good estimate of organ-absorbed dose.

"Scout No Scan" Technique Reduces Patient Radiation Exposure During CT-Guided Spine Biopsy

OBJECTIVE

The objective of this article is to report our experience with a technique for CT-guided spine biopsies that we refer to as the "scout no scan" technique.

CONCLUSION

The scout no scan technique can significantly lower radiation exposure while maintaining high diagnostic yields for CT-guided spinal biopsies.

THE SIZE-SPECIFIC DOSE ESTIMATE (SSDE) FOR TRUNCATED COMPUTED TOMOGRAPHY IMAGES

The purpose of this study is to investigate truncated axial computed tomography (CT) images in the clinical environment and to produce correction factors for abdomen, thoracic and head regions based on clinical data, in order to accurately predict the water-equivalent diameter (DW) and size-specific dose estimate (SSDE). We investigated axial images of 75 patients who underwent CT examinations. Truncated axial images were characterized by the truncation percentage (TP). Correction factors were calculated by using the value of DW for a certain TP (truncated image) divided by the value of DW for TP = 0% (the non-truncated image). Most of the thorax images acquired for this study were truncated images (86.2%), in the abdomen region about half of the images were truncated (48.1%), and in the head region only a small portion were truncated (9.1%). In the thorax region the value of TP for the truncated images varied up to 50%, in the abdomen region it varied up to 35%, and in the head region it was smaller than 10%. We have shown how to accurately estimate DW and SSDE by applying a correction factor to the truncated images. The correction factors increase exponentially with increasing TP. The corrected DW and SSDE for the truncated images were significant in the thoracic region, but were not significant in the abdomen and head regions.

Does gantry rotation time influence accuracy of volume computed tomography dose index (CTDIvol) in modern CT?

PURPOSE

The purpose of this study was to develop a gantry overrun corrected CTDI_vol (cCTDI_vol) dosimetry and evaluate the differences between the displayed CTDI_vol (dCTDI_vol), measured CTDI_vol (mCTDI_vol), and the cCTDI_vol.

METHODS AND MATERIALS

The each 8 rotation times between 275 and 1000ms of two CT scanners were investigated. Rotation time (T_rot) and the beam-on time (T_beam) in axial scanning were measured accurately to determine the gantry overrun time (T_over) as T_beam-T_rot. Subsequently, mCTDI_vol was measured by using a 100mm ionization chamber and CTDI phantoms. Furthermore, we introduced a gantry overrun correction factor (C_o=T_rot/T_beam) to obtain cCTDI_vol. Upon completion of the data acquisition, the dCTDI_vol and mCTDI_vol were compared with the cCTDI_vol.

RESULTS

The discrepancies of T_rot were 0.2±0.2ms as compared to the preset rotation times, and T_over was machine-specific and almost constant (22.4±0.5ms or 45.1±0.3ms) irrespective of the preset rotation time. Both dCTDI_vol and mCTDI_vol were increasingly overestimated compared to cCTDI_vol as the faster the preset rotation time was selected (1.7-23.5%).

CONCLUSION

The rotation time influences the accuracy of CTDI_vol in modern CT, and should be taken into consideration when assessing the radiation output in modern CT.

Evaluation of Effective Dose from CT Scans for Overweight and Obese Adult Patients Using the VirtualDose Software

This paper evaluates effective dose (ED) of overweight and obese patients who undergo body computed tomography (CT) examinations. ED calculations were based on tissue weight factors in the International Commission on Radiological Protection Publication 103 (ICRP 103). ED per unit dose length product (DLP) are reported as a function of the tube voltage, body mass index (BMI) of patient. The VirtualDose software was used to calculate ED for male and female obese phantoms representing normal weight, overweight, obese 1, obese 2 and obese 3 patients. Five anatomic regions (chest, abdomen, pelvis, abdomen/pelvis and chest/abdomen/pelvis) were investigated for each phantom. The conversion factors were computed from the DLP, and then compared with data previously reported by other groups. It was observed that tube voltage and BMI are the major factors that influence conversion factors of obese patients, and that ED computed using ICRP 103 tissue weight factors were 24% higher for a CT chest examination and 21% lower for a CT pelvis examination than the ED using ICRP 60 factors. For body CT scans, increasing the tube voltage from 80 to 140 kVp would increase the conversion factors by as much as 19-54% depending on the patient's BMI. Conversion factor of female patients was ~7% higher than the factors of male patients. DLP and conversion factors were used to estimate ED, where conversion factors depended on tube voltage, sex, BMI and tissue weight factors. With increasing number of obese individuals, using size-dependence conversion factors will improve accuracy, in estimating patient radiation dose.

Establishment of institutional diagnostic reference level for computed tomography with automated dose-tracking software

Introduction

The aim of this study was to establish institutional diagnostic reference levels (DRLs) by summarising doses collected across the five computed tomography (CT) system in our institution.

Methods

CT dose data of 15940 patients were collected retrospectively from May 2015 to October 2015 in five institutional scanners. The mean, 75th percentile and 90th percentile of the dose spread were calculated according to anatomic region. The common CT examinations such as head, chest, combined abdomen/pelvis (A/P), and combined chest/abdomen/pelvis (C/A/P) were reviewed. Distribution of CT dose index (CTDIvol), dose‐length product (DLP) and effective dose (ED) were extracted from the data for single‐phasic and multiphasic examinations.

Results

The institutional DRL for our CT units were established as mean (50th percentile) of CTDIvol (mGy), DLP (mGy.cm) and ED (mSv) for single and multiphasic studies using the dose‐tracking software. In single phasic examination, Head: (49.0 mGy), (978.0 mGy.cm), (2.4 mSv) respectively; Chest: (6.0 mGy), (254.0 mGy.cm), (4.9 mSv) respectively; CT A/P (10.0 mGy), (514.0 mGy.cm), (8.9 mSv) respectively; CT C/A/P (10.0 mGy), (674.0 mGy.cm), (11.8 mSv) respectively. In multiphasic studies: Head (45.0 mGy), (1822.0 mGy.cm), (5.0 mSv) respectively; Chest (8.0 mGy), (577.0 mGy.cm), (10.0 mSv) respectively; CT A/P: (10.0 mGy), (1153.0 mGy.cm), (20.2 mSv) respectively; CT C/A/P: (11.0 mGy), (1090.0 mGy.cm), (19.2 mSv) respectively.

Conclusions

The reported metrics offer a variety of information that institutions can use for quality improvement activities. The variations in dose between scanners suggest a large potential for optimisation of radiation dose.

Reducing radiation exposure with iterative reconstruction: an inter- and intra-scanner analysis

Our purpose in this study was to compare delivered radiation exposure via computed tomography dose index volume (CTDI_vol) and dose length production (DLP) measurements from computed tomography (CT) examinations performed on scanners with and without image-quality enhancing iterative reconstruction (IR) software. A retrospective analysis was conducted on randomly selected chest, abdomen, and/or pelvis CT examinations from three different scanners from 1 January 2013 to 31 December 2013. CTDI_vol and DLP measurements were obtained from two CT scanners with and one CT scanner without IR software. To evaluate inter-scanner variability, we compared measurements from the same model CT scanners, one with and one without IR software. To evaluate intra-scanner variability, we compared measurements between two scanners with IR software from different manufacturers. CT scanners with IR software aided in the overall reduction in radiation exposure, measured as CTDI_vol by 30% and DLP by 39% when compared to a scanner without IR. There was no significant difference in CTDl_vol or DLP measurements across different manufacturers with IR software. As a result, IR software significantly decreased the radiation exposure to patients, but there were no differences in radiation measurements across CT manufacturers with IR software.

Don't forget the dose: Improving computed tomography dosing for pediatric appendicitis

BACKGROUND

A pediatric computed tomography (CT) radiation dose reduction program was implemented throughout our children's associated hospital system in 2010. We hypothesized that the CT dose received for evaluation of appendicitis in children would be significantly higher among the 40 referral, nonmember hospitals (NMH) than the 9 member hospitals (MH).

METHODS

Preoperative CTs of pediatric (<18years) appendectomy patients between April 2012 and April 2015 were reviewed. Size specific dose estimate (SSDE), an approximation of absorbed dose incorporating patient diameter, and Effective Dose (ED) were calculated for each scan.

RESULTS

1128 (65%) of 1736 appendectomy patients underwent preoperative CT. 936 patients seen at and 102 children evaluated at NMH had dosing and patient diameter data for analysis. SSDE and ED were significantly higher with greater variance at NMH across all ages (all p<0.05, Figure). NMH's SSDE and ED also exceeded reference levels.

CONCLUSION

Radiation exposure in CT scans for evaluation of pediatric appendicitis is significantly higher and more variable in NMH. A proactive approach to reduce dose, in addition to frequency, of CT scans in pediatric patients is essential.

LEVEL OF EVIDENCE

Level III.

The Role of Limited Head Computed Tomography in the Evaluation of Pediatric Ventriculoperitoneal Shunt Malfunction

BACKGROUND

The evaluation of children with suspected ventriculoperitoneal shunt (VPS) malfunction has evolved into a diagnostic dilemma. This patient population is vulnerable not only to the medical risks of hydrocephalus and surgical complications but also to silent but harmful effects of ionizing radiation secondary to imaging used to evaluate shunt efficacy and patency. The combination of increased medical awareness regarding ionizing radiation and public concern has generated desire to reduce the reliance on head computed tomography (CT) for the evaluation of VPS malfunction. Many centers have started to investigate the utility of low-dose CT scans and alternatives, such as fast magnetic resonance imaging for the investigation of VP shunt malfunction in order to keep radiation exposure as low as reasonably achievable. This pilot study hopes to add to the armamentarium available to the clinician charged with evaluating this challenging patient population by testing the feasibility of a limited CT protocol as an alternative to a full head CT examination.

OBJECTIVE

To evaluate the efficacy of a limited head CT protocol compared with a complete head CT for the evaluation of children presenting to the pediatric emergency department with suspected shunt malfunction.

METHODS

We retrospectively reviewed all pediatric patients who received a head CT for suspected VPS malfunction evaluation at a tertiary care children's hospital from January 2001 through January 2013. Children were included in the pilot study if they had at least 2 CT scans in this study period interpreted by a specific senior attending neuroradiologist. For each patient enrolled, a limited series was generated from the most recent CT scan by selecting four representative axial slices based on the sagittal scout image. These 4 slices where selected at the level of the fourth ventricle, third ventricle, basal ganglia level, and lateral ventricles, respectively. A blinded, senior attending neuroradiologist first reviewed the limited 4-slice CT data set and was asked to determine if the ventricular system had increased, decreased, or remained stable. Subsequently, the neuroradiologist compared their interpretation of the limited examination with the official report from the full CT data set as the standard of reference as well as the interpretation of the most recent prior scan.

RESULTS

Forty-six patients (age range, 2 months to 18 years; average age, 6.4 years (SD, 4.2), 54% male) were included in the study. Forty-four of 46 (95.7%) limited CT scans matched the official report of the full CT scan. No cases of increased ventricular size were missed (100% positive predictive value for increased ventricular size). The use of a limited head CT (4 axial images) instead of a complete head CT (average of 31 axial images in our studied patients) confers a radiation dose reduction of approximately 87%.

CONCLUSIONS

Our pilot study demonstrates that utilization of limited head CT scan in the evaluation of children with suspected VP shunt malfunction is a feasible strategy for the evaluation of the ventricular size. Further prospective and multidisciplinary studies are needed to evaluate the reliability of limited head CT for the clinical evaluation of VP shunt malfunction.

Instituting a Low-dose CT-guided Lung Biopsy Protocol

RATIONALE AND OBJECTIVES

We aimed to evaluate whether implementation of a low-dose computed tomography (CT)-guided lung biopsy protocol, with the support of individual radiologists in the section, would lead to immediate and sustained decreases in radiation dose associated with CT-guided lung biopsies.

MATERIALS AND METHODS

A low-dose CT-guided lung biopsy protocol was developed with modifications of kilovoltage peak, milliamperes, and scan coverage. Out of 413 CT-guided lung biopsies evaluated over a 3-year period beginning in 2009, 175 performed with a standard protocol before the development of a low-dose protocol, and 238 performed with a low-dose protocol. The dose-length product (DLP) was recorded for each lung biopsy and retrospectively compared between the two protocols. Individual radiologist level DLPs were also compared before and after the protocol change.

RESULTS

The mean biopsy dose decreased by 64.4% with the low-dose protocol (113.8 milligray centimeters versus 319.7 milligray centimeters; P < 0.001). This decrease in radiation dose persisted throughout the entire 18 months evaluated following the protocol change. After the protocol change, each attending radiologist demonstrated a decrease in administered radiation dose. The diagnostic outcome rate and complication rate were unchanged over the interval.

CONCLUSIONS

Implementation of a low-dose CT-guided lung biopsy protocol resulted in an immediate reduction in patient radiation dose that was seen with all attending radiologists and persisted for at least 18 months. Such an intervention may be considered at other institutions wishing to reduce patient doses.

How accurate is size-specific dose estimate in pediatric body CT examinations?

BACKGROUND

Size-specific dose estimate is gaining increased acceptance as the preferred index of CT dose in children. However it was developed based on non-clinical data.

OBJECTIVE

To compare the accuracy of size-specific dose estimate (SSDE) based on geometric and body weight measures in pediatric chest and abdomen CT scans, versus the more accurate [Formula: see text] (mean SSDE based on water-equivalent diameter).

MATERIALS AND METHODS

We retrospectively identified 50 consecutive children (age <18 years) who underwent chest CT examination and 50 children who underwent abdomen CT. We measured anteroposterior diameter (DAP) and lateral diameter (DLAT) at the central slice (of scan length) of each patient and calculated DAP+LAT (anteroposterior diameter plus lateral diameter) and DED (effective diameter) for each patient. We calculated the following in each child: (1) SSDEs based on DAP, DLAT, DAP+LAT, DED, and body weight, and (2) SSDE based on software calculation of mean water-equivalent diameter ([Formula: see text] adopted standard within our study). We used intraclass correlation coefficient (ICC) and Bland-Altman analysis to compare agreement between the SSDEs and [Formula: see text].

RESULTS

Gender and age distribution were similar between chest and abdomen CT groups; mean body weight was 37 kg for both groups, with ranges of 6-130 kg (chest) and 8-107 kg (abdomen). SSDEs had very strong agreement (ICC>0.9) with [Formula: see text]. SSDEs based on DLAT had 95% limits of agreement of up to 43% with [Formula: see text]. SSDEs based on other parameters (body weight, DAP, DAP+LAT, DED) had 95% limits of agreement of up to 25%.

CONCLUSION

Differences between SSDEs calculated using various indications of patient size (geometric indices and patient weight) and the more accurate [Formula: see text] calculated using proprietary software were generally small, with the possible exception for lateral diameter, and provide acceptable dose estimates for body CT in children.

CT Radiation: Key Concepts for Gentle and Wise Use

Use of computed tomography (CT) in medicine comes with the responsibility of its appropriate (wise) and safe (gentle) application to obtain required diagnostic information with the lowest possible dose of radiation. CT provides useful information that may not be available with other imaging modalities in many clinical situations in children and adults. Inappropriate or excessive use of CT should be avoided, especially if required information can be obtained in an accurate and time-efficient manner with other modalities that require a lower radiation dose, or non-radiation-based imaging modalities such as ultrasonography and magnetic resonance imaging. In addition to appropriate use of CT, the radiology community also must monitor scanning practices and protocols. When appropriate, high-contrast regions and lesions should be scanned with reduced dose, but overly zealous dose reduction should be avoided for assessment of low-contrast lesions. Patients' cross-sectional body size should be taken into account to deliver lower radiation dose to smaller patients and children. Wise use of CT scanning with gentle application of radiation dose can help maximize the diagnostic value of CT, as well as address concerns about potential risks of radiation. In this article, key concepts in CT radiation dose are reviewed, including CT dose descriptors; radiation doses from CT procedures; and factors and technologies that affect radiation dose and image quality, including their use in creating dose-saving protocols. Also discussed are the contributions of radiation awareness campaigns such as the Image Gently and Image Wisely campaigns and the American College of Radiology Dose Index Registry initiatives.

Automated Calculation of Water-equivalent Diameter (DW) Based on AAPM Task Group 220

The purpose of this study is to accurately and effectively automate the calculation of the water‐equivalent diameter (DW) from 3D CT images for estimating the size‐specific dose. DW is the metric that characterizes the patient size and attenuation. In this study, DW was calculated for standard CTDI phantoms and patient images. Two types of phantom were used, one representing the head with a diameter of 16 cm and the other representing the body with a diameter of 32 cm. Images of 63 patients were also taken, 32 who had undergone a CT head examination and 31 who had undergone a CT thorax examination. There are three main parts to our algorithm for automated DW calculation. The first part is to read 3D images and convert the CT data into Hounsfield units (HU). The second part is to find the contour of the phantoms or patients automatically. And the third part is to automate the calculation of DW based on the automated contouring for every slice (DW,all). The results of this study show that the automated calculation of DW and the manual calculation are in good agreement for phantoms and patients. The differences between the automated calculation of DW and the manual calculation are less than 0.5%. The results of this study also show that the estimating of DW,all using DW,n=1 (central slice along longitudinal axis) produces percentage differences of −0.92%±3.37% and 6.75%±1.92%, and estimating DW,all using DW,n=9 produces percentage differences of 0.23%±0.16% and 0.87%±0.36%, for thorax and head examinations, respectively. From this study, the percentage differences between normalized size‐specific dose estimate for every slice (nSSDEall) and nSSDEn=1 are 0.74%±2.82% and −4.35%±1.18% for thorax and head examinations, respectively; between nSSDEall and nSSDEn=9 are 0.00%±0.46% and −0.60%±0.24% for thorax and head examinations, respectively.

PACS number(s): 87.57.Q‐, 87.57.uq‐

Reducing Patient Radiation Exposure From CT Fluoroscopy-Guided Lumbar Spine Pain Injections by Targeting the Planning CT

OBJECTIVE

CT fluoroscopy-guided lumbar spine pain injections typically include a preprocedural planning CT that contributes considerably to patient dose. The purpose of this study was to quantify the degree of radiation exposure reduction achieved by modifying only the planning CT component of the examination.

MATERIALS AND METHODS

A retrospective review was performed of 80 CT fluoroscopy-guided lumbar spine injections. Forty patients were scanned with a standard protocol using automatic tube current modulation (method A). Another 40 patients were scanned using a new technique that fixed the tube current of the planning CT to either 50 or 100 mA on the basis of the patient's anteroposterior diameter and that reduced the z-axis coverage (method B). Dose-length products (DLPs) were compared for the two methods.

RESULTS

The mean maximal tube current for the planning CT was 435.0 mA for method A and 67.5 mA for method B. The mean z-axis was shorter for method B at 6.5 cm than for method A at 9.6 cm (p < 0.0001). The mean DLP for the planning CT was 11 times lower for method B than for method A: 27.9 versus 313.1 mGy × cm, respectively (p < 0.0001). When method B was used, the mean DLP for the total procedure (i.e., planning CT plus CT fluoroscopy components) was reduced by 78%. There was no significant difference between methods A and B in CT fluoroscopy time (p = 0.37). All procedures were technically successful.

CONCLUSION

A nearly fivefold reduction in radiation exposure can be achieved in CT fluoroscopy-guided lumbar spine pain injections through modifications to the planning CT alone.

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.

Radiation Dose Survey for Common Computed Tomography Exams: 2013 British Columbia Results

In 2013 Health Canada conducted a national survey of computed tomography (CT) radiation usage. We analysed contributions from all 7 public health authorities in the province of British Columbia, which covered scanner age, number of slices, and common adult protocols (≥19 years: 70 ± 20 kg, head, chest, abdomen/pelvis, and trunk). Patient doses were recorded for common protocols. Diagnostic reference levels (DRLs) was calculated using scanner data with >10 patient doses recorded for each protocol. Data was analysed based on image reconstruction (filtered backprojection vs iterative reconstruction [IR] vs IR available but not in use). Provincial response was 92%, with 59 of 64 CT data used for analysis. The average scanner age was 5.5 years old, with 39% of scanners installed between 2008-2013; 78.5% of scanners were multislice (>64 slices), and 44% of scanners had IR available. Overall British Columbia DRLs were: head = 1305, chest = 529, abdomen/pelvis = 819, and trunk = 1225. DRLs were consistent with Health Canada recommendations and other Canadian published values, but above international standards. For sites with IR available, less than 50% used this technology routinely for head, chest and trunk exams. Overall, use of IR reduced radiation usage between 11%-32% compared to filtered backprojection, while sites using IR vs IR available used 30%/43% less radiation for head/chest exams ( P < .05). No significant difference was observed for abdomen/pelvis exams ( P = .385). With the fast pace of CT technical advancement, DRLs should reflect the technology used, instead of just globally applied to anatomical regions. Federal guidelines should be updated at a higher frequency to reflect new technology. In addition, new technologies must be utilised to optimize image quality vs radiation usage.

Radiation Doses of Various CT Protocols: a Multicenter Longitudinal Observation Study

Emerging concerns regarding the hazard from medical radiation including CT examinations has been suggested. The purpose of this study was to observe the longitudinal changes of CT radiation doses of various CT protocols and to estimate the long-term efforts of supervising radiologists to reduce medical radiation. Radiation dose data from 11 representative CT protocols were collected from 12 hospitals. Attending radiologists had collected CT radiation dose data in two time points, 2007 and 2010. They collected the volume CT dose index (CTDIvol) of each phase, number of phases, dose length product (DLP) of each phase, and types of scanned CT machines. From the collected data, total DLP and effective dose (ED) were calculated. CTDIvol, total DLP, and ED of 2007 and 2010 were compared according to CT protocols, CT machine type, and hospital. During the three years, CTDIvol had significantly decreased, except for dynamic CT of the liver. Total DLP and ED were significantly decreased in all 11 protocols. The decrement was more evident in newer CT scanners. However, there was substantial variability of changes of ED during the three years according to hospitals. Although there was variability according to protocols, machines, and hospital, CT radiation doses were decreased during the 3 years. This study showed the effects of decreased CT radiation dose by efforts of radiologists and medical society.

Radiation doses to emergency department patients undergoing computed tomography

OBJECTIVES

Computed tomography (CT) use is increasing in the emergency department (ED). Many physicians are concerned about exposing patients to radiation from CT scanning, but estimates of radiation doses vary. This study's objective was to determine the radiation doses from CT scanning for common indications in a Canadian ED using modern multidetector CT scanners.

METHODS

We conducted a health records review of consecutive adult patients seen at two busy tertiary care EDs over a 2-month period who underwent CT scanning ordered by emergency physicians. Cases were identified by searching an imaging database. Data collected included patient age and sex, study indication, scanner model, body area, and reported dose-length product. Effective dose per scan was calculated from reported dose-length product. Data were collected on a standardized form, entered into an electronic database, and analyzed with descriptive statistics and 95% CIs.

RESULTS

During the study period, emergency physicians assessed 19,880 patients. Overall, 2,720 (13.7%) underwent CT scanning, and of these, 144 (5.3%) patients had more than one scan. Patients had a mean age of 59.0 years, and 45.3% were men. Mean doses for the most common indications were as follows: simple head, 2.9 mSv; cervical spine, 5.7 mSv; complex head, 9.3 mSv; CT pulmonary angiogram, 11.2 mSv; abdomen (nontraumatic abdominal pain), 15.4 mSv; and abdomen (renal colic), 9.8 mSv.

CONCLUSIONS

Approximately one in seven ED patients had a CT scan. Emergency physicians should be aware of typical radiation doses for the studies they order and how the dose varies by protocol and indication.

Initial Performance of Radiologists and Radiology Residents in Interpreting Low-Dose (2-mSv) Appendiceal CT

OBJECTIVE

The objective of our study was to prospectively evaluate the initial diagnostic performance and learning curve of a community of radiologists and residents in interpreting 2-mSv appendiceal CT.

SUBJECTS AND METHODS

We included 46 attending radiologists and 153 radiology residents from 22 hospitals who completed an online training course of 30 2-mSv CT cases. Appendicitis was confirmed in 14 cases. Most of the readers had limited (≤ 10 cases, n = 32) or no (n = 118) prior experience with low-dose appendiceal CT. The order of cases was randomized for each reader. A multireader multicase ROC analysis was performed. Generalized estimating equations were used to model the learning curves in diagnostic performance.

RESULTS

Diagnostic performance gradually improved with years of training. The average AUC was 0.94 (95% CI, 0.90-0.98), 0.92 (0.88-0.96), 0.90 (0.85-0.96), and 0.86 (0.80-0.92) for the attending radiologists, senior residents, 2nd-year residents, and 1st-year residents, respectively. We did not observe any notable intrareader learning curves over the training course of the 30 cases except a decrease in reading time. Diagnostic accuracy and sensitivity were significantly affected by the reader training level and prior overall experience with appendiceal CT but not by the prior specific experience with low-dose appendiceal CT.

CONCLUSION

The learning curve is likely prolonged and forms gradually over years by overall radiology training and clinical experience in general rather than by experience with low-dose appendiceal CT specifically.

Percutaneous Transthoracic Lung Biopsy: Comparison Between C-Arm Cone-Beam CT and Conventional CT Guidance

BACKGROUND: C-arm cone-beam computed tomography (CBCT) is a comparatively novel modality for guiding percutaneous transthoracic lung biopsies (PTLBs), and despite its potential advantages over conventional computed tomography (CCT), a head-to-head comparison of the two techniques has yet to be reported in the literature. This study aims to evaluate the diagnostic value and safety of CBCT-guided PTLB compared to CCT-guided biopsy, with cases performed in a single hospital. METHODS: A total of 104 PTLB patients were retrospectively analyzed in this study. 35 PTLBs were performed under CBCT guidance, and 69 PTLBs were performed under CCT guidance. Diagnostic accuracy, sensitivity, and specificity for malignancy as well as procedure time, radiation dose of patients, and complication rate in the two groups were compared. RESULTS: Total procedure time was significantly lower in the CBCT group (32 ± 11 minutes) compared to the CCT group (38 ± 9.7 minutes; P = .009), especially among patients ≥ 70 years of age (CBCT: 33 ± 12 minutes, CCT: 42 ± 13, P = .022). For lesions in the lower lobes, the CBCT-guided group received significantly reduced effective radiation dose (2.9 ± 1.6 mSv) than CCT-guided patients (3.7 ± 0.80; P = .042). Diagnostic accuracy, sensitivity, and specificity for malignancy were comparable between the two groups, as were post-biopsy complication rates. CONCLUSION: CBCT guidance significantly reduces the procedure time and radiation exposure for PTLBs compared with CCT, and should be considered in clinical settings that may be difficult or time-consuming to perform under CCT.

Feasibility of using the computed tomography dose indices to estimate radiation dose to partially and fully irradiated brains in pediatric neuroradiology examinations

The purpose of this study was two-fold: (a) to measure the dose to the brain using clinical protocols at our institution, and (b) to develop a scanner-independent dosimetry method to estimate brain dose. Radiation dose was measured with a pediatric anthropomorphic phantom and MOSFET detectors. Six current neuroradiology protocols were used: brain, sinuses, facial bones, orbits, temporal bones, and craniofacial areas. Two different CT vendor scanners (scanner A and B) were used. Partial volume correction factors (PVCFs) were determined for the brain to account for differences between point doses measured by the MOSFETs and average organ dose. The CTDIvol and DLP for each protocol were recorded. The dose to the brain (mGy) for scanners A and B was 10.7 and 10.0 for the brain protocol, 7.8 and 3.2 for the sinus, 10.2 and 8.6 for the facial bones, 7.4 and 4.7 for the orbits and 1.6 and 1.9 for the temporal bones, respectively. On scanner A, the craniofacial protocol included a standard and high dose option; the dose measured for these exams was 3.9 and 16.9 mGy, respectively. There was only one craniofacial protocol on scanner B; the brain dose measured on this exam was 4.8 mGy. A linear correlation was found between DLP and brain dose with the conversion factors: 0.049 (R(2) = 0.87), 0.046 (R(2) = 0.89) for scanner A and B, and 0.048 (R(2) = 0.89) for both scanners. The range of dose observed was between 1.8 and 16.9 mGy per scan. This suggests that brain dose estimates may be made from DLP.