AAPM Task Group Report 261: Comprehensive quality control methodology and management of dental and maxillofacial cone beam computed tomography (CBCT) systems.

Cone-beam computed tomography (CBCT) systems specifically designed and manufactured for dental, maxillofacial imaging (MFI) and otolaryngology (OLR) applications have been commercially available in the United States since 2001 and have been in widespread clinical use since. Until recently, there has been a lack of professional guidance available for medical physicists about how to assess and evaluate the performance of these systems and about the establishment and management of quality control (QC) programs. The owners and users of dental CBCT systems may have only a rudimentary understanding of this technology, including how it differs from conventional multidetector CT (MDCT) in terms of acceptable radiation safety practices. Dental CBCT systems differ from MDCT in several ways and these differences are described. This report provides guidance to medical physicists and serves as a basis for stakeholders to make informed decisions regarding how to manage and develop a QC program for dental CBCT systems. It is important that a medical physicist with experience in dental CBCT serves as a resource on this technology and the associated radiation protection best practices. The medical physicist should be involved at the pre-installation stage to ensure that a CBCT room configuration allows for a safe and efficient workflow and that structural shielding, if needed, is designed into the architectural plans. Acceptance testing of new installations should include assessment of mechanical alignment of patient positioning lasers and x-ray beam collimation and benchmarking of essential image quality performance parameters such as image uniformity, noise, contrast-to-noise ratio (CNR), spatial resolution, and artifacts. Several approaches for quantifying radiation output from these systems are described, including simply measuring the incident air-kerma (Kair) at the entrance surface of the image receptor. These measurements are to be repeated at least annually as part of routine QC by the medical physicist. QC programs for dental CBCT, at least in the United States, are often driven by state regulations, accreditation program requirements, or manufacturer recommendations.

A Novel and Simple Method Using Computed Tomography Streak Artifact to Determine the Orientation of Directional Deep Brain Stimulation Leads.

BACKGROUND AND OBJECTIVES: Directional leads have garnered widespread use in deep brain stimulation (DBS) because of the ability to steer current and maximize the therapeutic window. Accurate identification of lead orientation is critical to effective programming. Although directional markers are visible on 2-dimensional imaging, precise orientation may be difficult to interpret. Recent studies have suggested methods of determining lead orientation, but these involve advanced intraoperative imaging and/or complex computational algorithms. Our objective is to develop a precise and reliable method of determining orientation of directional leads using conventional imaging techniques and readily available software. METHODS: We examined postoperative thin-cut computed tomography (CT) scans and x-rays of patients who underwent DBS with directional leads from 3 vendors. Using commercially available stereotactic software, we localized the leads and planned new trajectories precisely overlaying the leads visualized on CT. We used trajectory view to locate the directional marker in a plane orthogonal to the lead and inspected the streak artifact. We then validated this method with a phantom CT model by acquiring thin-cut CT images orthogonal to 3 different leads in various orientations confirmed under direct visualization. RESULTS: The directional marker creates a unique streak artifact that reflects the orientation of the directional lead. There is a hyperdense symmetric streak artifact parallel to the axis of the directional marker and a symmetric hypodense dark band orthogonal to the marker. This is often sufficient to infer the direction of the marker. If not, it at least renders 2 opposite possibilities for the direction of the marker, which can then be easily reconciled by comparison with x-ray images. CONCLUSION: We propose a method to determine orientation of directional DBS leads in a precise manner on conventional imaging and readily available software. This method is reliable across DBS vendors, and it can simplify this process and aid in effective programming.

Impact of multidetector computed tomography scan parameters, novel reconstruction settings, and lung nodule characteristics on nodule diameter measurements: A phantom study.

PURPOSE: Novel CT reconstruction techniques strive to maintain image quality and processing efficiency. The purpose of this study is to investigate the impact of a newer hybrid iterative reconstruction technique, Adaptive Statistical Iterative Reconstruction-V (ASIR-V), in combination with various CT scan parameters on the semi-automated quantification using various lung nodules. METHODS: A chest phantom embedded with eight spherical objects was scanned using varying CT parameters such as tube current and ASIR-V levels. We calculated absolute percentage error (APE) and mean APE (MAPE) using differences between the semi-automated measured diameters and known dimensions. Predictive variables were assessed using a multivariable general linear model. The linear regression slope coefficients (ß) were reported to demonstrate effect size and directionality. RESULTS: The APE of the semi-automated measured diameters was higher in ground-glass than solid nodules (ß = 9.000, p < 0.001). APE had an inverse relationship with nodule diameter (mm; ß = -3.499, p < 0.001) and tube current (mA; ß = -0.006, p < 0.001). MAPE did not vary based on the ASIR-V level (range: 5.7%-13.1%). CONCLUSION: Error is dominated by nodule characteristics with a small effect of tube current. Regardless of phantom size, nodule size accuracy is not affected by tube voltage or ASIR-V level, maintaining accuracy while maximizing radiation dose reduction.

Dose, Benefit, and Risk in Medical Imaging, 1st Edition.

When interacting with colleagues, patients, and members of the public, medical physicists are frequently asked questions about radiation doses, clinical benefits, and biological risks of medical imaging. This book collects some of the latest data and understanding on these subjects into a single concise and well-organized volume and makes it accessible to a wide variety of potential readers. The editors and many of the chapter authors are from Memorial Sloan Kettering Cancer Center. Despite the variety of authors, the content is well-organized and fits together seamlessly.

A Phantom Study and a Retrospective Clinical Analysis to Investigate the Impact of a New Image Processing Technology on Radiation Dose and Image Quality during Hepatic Embolization.

PURPOSE: To investigate changes in radiation dose and image quality using phantoms and hepatic embolization procedures performed with a new image processing technology (ClarityIQ) for a single-plane flat-detector-based interventional fluoroscopy system. MATERIALS AND METHODS: Phantom study was performed using acrylic sheets simulating different patient sizes. Air kerma rates (AKRs) were compared for different fluoroscopy modes and magnification modes without and with ClarityIQ. Repeat hepatic embolization procedures performed on the same lobe of the liver in the same patient by the same interventional radiologist between January 2013 and July 2014 without and with ClarityIQ were evaluated retrospectively. This included treatment of 33 hepatic lobes in 26 patients. Cumulative air kerma (CAK), kerma-area product (KAP), and factors affecting radiation dose were extracted from study metadata and compared. Blinded randomized image quality review was performed on arteriograms using a five-point scale. RESULTS: The phantom study revealed a significantly lower AKR (P < .005) with ClarityIQ. Repeated-measures analysis revealed a significant effect of ClarityIQ (P ≤ .001) on CAK and KAP, with reductions ranging between 9% and 85% (median, 67%) and between 5% and 89% (median, 75%), respectively, on a case-by-case basis. Mean reductions in CAK and KAP were 279 mGy and 134,030 mGy·cm(2), respectively. Image quality review scores were significantly lower (P ≤ .001) with ClarityIQ, effecting visualization of tumor vasculature and appearance of noise texture. CONCLUSIONS: ClarityIQ resulted in radiation dose reduction in the phantom study and in the hepatic embolization procedures, but with a decrease in subjective perceptions of image quality.

Evaluation of coronary artery image quality with knowledge-based iterative model reconstruction.

RATIONALE AND OBJECTIVES: To evaluate knowledge-based iterative model reconstruction (IMR) to improve image quality and reduce radiation dose in coronary computed tomography angiography (cCTA). MATERIALS AND METHODS: We evaluated 45 consecutive cCTA studies, including 25 studies performed with an 80% systolic dose reduction using tube current modulation (TCM). Each study was reconstructed with filtered back projection (FBP), hybrid iterative reconstruction (iDose(4)), and IMR in a diastolic phase. Additional systolic phase reconstructions were obtained for TCM studies. Mean pixel attenuation value and standard deviation (SD) were measured in the left ventricle and left main coronary artery. Subjective scores were obtained by two independent reviewers on a 5-point scale for definitions of contours of small coronary arteries (<3 mm), coronary calcifications, noncalcified plaque, and overall diagnostic confidence for the presence/absence of stenosis. RESULTS: There was no significant difference in pixel intensity among FBP, iDose(4), and IMR (P > .8). For diastolic phase images, noise amplitude in the left main coronary artery was reduced by a factor of 1.3 from FBP to iDose(4) (SD = 99 vs. 74; P = .005) and by a factor of 2.6 from iDose(4) to IMR (SD = 74 vs. 28; P < .001). For systolic phase TCM images, noise amplitude in the left main coronary artery was reduced by a factor of 2.3 from FBP to iDose(4) (SD = 322 vs. 142; P < .001) and by a factor of 3.0 from iDose(4) to IMR (SD = 142 vs. 48; P < .001). All four subjective image quality scores were significantly better with IMR compared to iDose(4) and FBP (P < .001). The reduction in image noise amplitude and improvement in image quality scores were greatest among obese patients. CONCLUSIONS: IMR reduces intravascular noise on cCTA by 86%-88% compared to FBP, and improves image quality at radiation exposure levels 80% below our standard technique.

Flow diversion versus traditional aneurysm embolization strategies: analysis of fluoroscopy and procedure times.

BACKGROUND AND OBJECTIVE: Flow diverters are increasingly used for treatment of complex intracranial aneurysms. The purpose of this study was to compare the pipeline embolization device (PED) and traditional embolization strategies in terms of fluoroscopy and procedure time. MATERIAL AND METHODS: Fluoroscopy and procedure times (in minutes) were retrospectively analyzed and compared between 127 patients treated with the PED, 86 patients treated with single stage stent assisted coiling (SAC), and 16 patients treated with Onyx HD 500 at our institution. A multivariate logistic regression analysis was performed to determine independent predictors of fluoroscopy and procedure time. RESULTS: The three groups were comparable with respect to patient age, gender, and ruptured/unruptured aneurysm status. Aneurysms treated with the PED were significantly larger than stent coiled aneurysms, and aneurysm location distribution differed significantly between the three groups. Mean fluoroscopy time was significantly increased in the SAC (55±31 min, p<0.001) and Onyx HD 500 (91±36 min, p<0.001) groups relative to the PED group (34±23 min). Likewise, mean procedure time was significantly longer in SAC (155±50 min, p<0.001) and Onyx HD 500 (176±65 min, p<0.001) patients compared with PED patients (131±36 min). In multivariate analysis, SAC/Onyx HD 500 versus PED independently predicted longer procedure and fluoroscopy times. CONCLUSIONS: PED treatment requires significantly shorter fluoroscopy and procedure times compared with SAC and Onyx HD 500. The results of this study may be used by advocates of flow diverters as an additional argument for using this treatment modality to treat intracranial aneurysms.

Cost and radiation savings of partial substitution of ultrasound for CT in appendicitis evaluation: a national projection.

OBJECTIVE: The costs of an ultrasound-CT protocol and a CT-only protocol for an appendicitis evaluation are compared. For the ultrasound-CT protocol, patients with right lower quadrant abdominal pain undergo an ultrasound examination. If it is positive for appendicitis, they are sent directly to surgery, avoiding CT. MATERIALS AND METHODS: A comparative effectiveness research study was conducted. The costs of imaging tests, excess surgeries, and excess surgical deaths for the ultrasound-CT protocol and the costs of imaging tests and excess cancer deaths in the CT-only protocol were estimated. Data sources were Centers for Medicare & Medicaid Services (CMS) datasets, national hospital discharge surveys, radiology information system cases, and U.S. Census Bureau life tables. A meta-analysis and sensitivity analyses were also conducted. RESULTS: The meta-analysis showed a positive predictive value of 92.5% for CT and 91.0% for ultrasound. Analysis of CMS files showed that utilization of CT was almost exactly 2.0 examinations (one abdominal and one pelvic) per patient and for ultrasound was almost nil. The cost of this imaging protocol was $547 per patient, whereas the cost of a limited ultrasound study would be $88 per patient. For the total U.S. population, the cost savings in imaging minus the cost of extra surgeries and extra surgical deaths is $24.9 million per year. Following model VII proposed by the Committee on the Biological Effects of Ionizing Radiation (BEIR), which is known as "BEIR VII," the avoidance of a 12.4-mSv exposure for 262,500 persons would prevent 180 excess cancer deaths. The value of the years of life lost would be $339.5 million. The sensitivity analyses indicate that the cost savings are robust. CONCLUSION: An ultrasound-CT protocol for appendicitis evaluation offers potentially large savings over the standard CT-only protocol. There are moderate savings from using a less expensive imaging technique despite extra surgeries and large savings from radiation exposure avoided.

Extraction of CT dose information from DICOM metadata: automated Matlab-based approach.

OBJECTIVE: The purpose of this study was to extract exposure parameters and dose-relevant indexes of CT examinations from information embedded in DICOM metadata. CONCLUSION: DICOM dose report files were identified and retrieved from a PACS. An automated software program was used to extract from these files information from the structured elements in the DICOM metadata relevant to exposure. Extracting information from DICOM metadata eliminated potential errors inherent in techniques based on optical character recognition, yielding 100% accuracy.

An exposure indicator for digital radiography: AAPM Task Group 116 (executive summary).

Digital radiographic imaging systems, such as those using photostimulable storage phosphor, amorphous selenium, amorphous silicon, CCD, and MOSFET technology, can produce adequate image quality over a much broader range of exposure levels than that of screen/film imaging systems. In screen/film imaging, the final image brightness and contrast are indicative of over- and underexposure. In digital imaging, brightness and contrast are often determined entirely by digital postprocessing of the acquired image data. Overexposure and underexposures are not readily recognizable. As a result, patient dose has a tendency to gradually increase over time after a department converts from screen/film-based imaging to digital radiographic imaging. The purpose of this report is to recommend a standard indicator which reflects the radiation exposure that is incident on a detector after every exposure event and that reflects the noise levels present in the image data. The intent is to facilitate the production of consistent, high quality digital radiographic images at acceptable patient doses. This should be based not on image optical density or brightness but on feedback regarding the detector exposure provided and actively monitored by the imaging system. A standard beam calibration condition is recommended that is based on RQA5 but uses filtration materials that are commonly available and simple to use. Recommendations on clinical implementation of the indices to control image quality and patient dose are derived from historical tolerance limits and presented as guidelines.

A novel approach to reduce breast radiation exposure with coronary CTA: angled axial image acquisition.

RATIONALE AND OBJECTIVES: To determine whether angled gantry acquisition might be used to image the heart with a shorter scan length and reduced breast exposure during coronary computed tomography angiography. MATERIALS AND METHODS: One hundred consecutive coronary computed tomography angiography examinations of female patients were retrospectively evaluated to define the angle between the long axis of the left heart and the axial imaging plane. The scan length required to image the entire left ventricle along with the coronary arteries was measured for an axial scan plane as well as for a scan plane parallel to the long axis of the left heart. The overlap between these imaging volumes and the lower portion of the breast was measured. RESULTS: The long axis of the left heart varied from 7 degrees to 54 degrees off the axial plane (mean 32 degrees +/- 7 degrees ). The required scan length to include the entire left ventricle and coronary arteries ranged from 8.2 to 12.4 cm (mean, 10.0 +/- 0.9 cm) for the axial scan plane and 5.6-10.1 cm (mean, 7.5 +/- 0.8 cm) for a scan plane parallel to the long axis of the heart (P < .001). cCTA in the axial plane required a 7.4 +/- 1.6 cm overlap with the lower breast, whereas cCTA in the long axis of the heart reduced the overlap to 4.5 +/- 1.8 cm (P < .001). CONCLUSIONS: Using an angled gantry approach, the coronary arteries can be fully imaged in a plane along the long axis of the left heart with a single 10-cm acquisition and with substantial reduction in amount of breast tissue within the irradiated field.

Radiation dose in a "triple rule-out" coronary CT angiography protocol of emergency department patients using 64-MDCT: the impact of ECG-based tube current modulation on age, sex, and body mass index.

OBJECTIVE: "Triple rule-out" coronary CT angiography (CTA) using 64-MDCT technology is a new approach for evaluating emergency department patients presenting with symptoms suggestive of acute coronary syndrome (ACS). Our objective was to evaluate the reduction in effective radiation dose through the use of tube current modulation in patients who underwent a triple rule-out coronary CTA evaluation and to document how effective radiation dose was impacted by patient age, sex, and body mass index (BMI). MATERIALS AND METHODS: A retrospective analysis of triple rule-out coronary CTA examinations performed on a 64-MDCT scanner was ordered on a prospective cohort of 267 consecutive low- to moderate-risk emergency department patients with suspected ACS from a single university hospital between October 2006 and March 2008. Tube current modulation was generally used in patients with heart rates below 65 beats per minute during the second half of the study period as a way to reduce radiation exposure. We calculated effective radiation exposure using actual patient coronary CTA scanning parameters by age, sex, and BMI. RESULTS: Among the 172 patients evaluated without tube current modulation, effective dose averaged (+/- SD) 18.0 +/- 5.6 mSv (range, 9.9-31.3 mSv). Of the 95 patients who underwent CTA examination with tube current modulation, effective dose was significantly lower at 8.75 +/- 2.64 mSv (range, 5.4-16.6 mSv; p < 0.0001) and image quality was better (p < 0.0001) as compared with examinations without tube current modulation. There were no significant radiation differences by patient age, but tube current modulation decreased radiation exposure by at least half. Among the studies in which tube current modulation was not used, women received less radiation than men (17.0 vs 19.5 mSv, respectively; p < 0.001). For the studies with tube current modulation, there were no radiation differences by sex. Obese patients received significantly more radiation than overweight and normal-weight patients in the non-tube current modulation groups (20.9 mSv vs 15.0 and 14.9 mSv, respectively; p < 0.0001) and in the tube current modulation groups (10.3 mSv vs 7.6 and 7.1 mSv, p < 0.0001). CONCLUSION: The overall effective radiation dose for triple rule-out coronary CTA was reduced by more than 50% with ECG-based tube current modulation without loss of image quality. Tube current modulation should be used for triple rule-out coronary CTA examinations whenever possible.