Timothy J. Blackburn

Strengthening the Argument for Rapid Brain MR Imaging: Estimation of Reduction in Lifetime Attributable Risk of Developing Fatal Cancer in Children with Shunted Hydrocephalus by Instituting a Rapid Brain MR Imaging Protocol in Lieu of Head CT

BACKGROUND AND PURPOSE: Children with shunted hydrocephalus have been undergoing surveillance neuroimaging, generally in the form of head CT, for evaluation of ventricular size. As the life expectancy of these children has improved due to better shunt technology and medical care, risks related to the ionizing radiation incurred during multiple head CT examinations that they are expected to undergo throughout their lifetime have become a concern. The purpose of this study is to estimate the LAR of developing fatal cancer due to head CT for ventricular size assessment in children with shunted hydrocephalus and to assess the impact of instituting a rapid brain MR imaging protocol in reducing radiation exposure. MATERIALS AND METHODS: Retrospective review of medical records yielded 182 patients who underwent neuroimaging for assessment of ventricular size. Available neuroimaging studies (head CT and rapid brain MR) were counted and annual neuroimaging frequency was calculated. It was assumed that these patients undergo a similar number of neuroimaging studies annually through 20 years of age. A risk estimate was calculated based on the BEIR VII report and effective doses obtained using the International Commission on Radiologic Protection Report 103 organ weighting factors. RESULTS: The mean annual neuroimaging study frequency was 2.1. Based on the average age of 1.89 years, it was assumed neuroimaging surveillance commences in the second year of life. LAR was calculated assuming that a patient undergoes neuroimaging in the form of head CT at this frequency (2/year) through 20 years of age. Assuming 2 scans are performed per year and the low-dose head CT protocol is used, approximately 1 excess lifetime fatal cancer would be generated per 230 patients; with standard head CT, there would be 1 excess lifetime fatal cancer per 97 patients. CONCLUSIONS: Children with shunted hydrocephalus are at increased risk of developing fatal cancer if they are to undergo surveillance using head CT. Implementation of a rapid brain MR imaging protocol with no radiation detriment will reduce this risk.

Ionizing Radiation in Craniofacial Surgery: A Primer on Dose and Risks

An understanding of radiation dose and the anticipated risk to the patient is an important aspect of ordering radiological imaging studies responsibly. It is especially true for the pediatric practitioner because children are more vulnerable to the biological effects of radiation, such as radiosensitivity, longer lifetime years, and higher cellular mitotic activity. The use of fluoroscopy and computed tomography is commonplace in the practice of craniofacial surgery, but often dose reports from varied investigations are not directly comparable, and the risk of patient harm from the investigation is unclear. This article presents the fundamentals of radiation, dose, and risk as it applies to radiological imaging and also introduces our low dose craniofacial computed tomography protocol.

Radiation exposure and safety practices during pediatric central line placement.

PURPOSE Pediatric surgeons routinely use fluoroscopy for central venous line (CVL) placement. We examined radiation safety practices and patient/surgeon exposure during fluoroscopic CVL. METHODS Fluoroscopic CVL procedures performed by 11 pediatric surgeons in 2012 were reviewed. Fluoroscopic time (FT), patient exposure (mGy), and procedural data were collected. Anthropomorphic phantom simulations were used to calculate scatter and dose (mSv). Surgeons were surveyed regarding safety practices. RESULTS 386 procedures were reviewed. Median FT was 12.8 seconds. Median patient estimated effective dose was 0.13 mSv. Median annual FT per surgeon was 15.4 minutes. Simulations showed no significant difference (p=0.14) between reported exposures (median 3.5 mGy/minute) and the modeled regression exposures from the C-arm default mode (median 3.4 mGy/minute). Median calculated surgeon exposure was 1.5 mGy/year. Eight of 11 surgeons responded to the survey. Only three reported 100% lead protection and frequent dosimeter use. CONCLUSION We found nonstandard radiation training, safety practices, and dose monitoring for the 11 surgeons. Based on simulations, the C-arm default setting was typically used instead of low dose. While most CVL procedures have low patient/surgeon doses, every effort should be used to minimize patient and occupational exposure, suggesting the need for formal hands-on training for nonradiologist providers using fluoroscopy.

Tools for interactive analysis and display of fMRI data

Functional magnetic resonance imaging (fMRI) experiments are becoming recognized in a number of areas of neuroscience. Presenting useful information to the clinician in a reasonable time and in an understandable way is of paramount importance for the use of fMRI protocols in the clinical setting. We have developed a series of tools for fMRI analysis and presentation encapsulated by a commercially-available graphical-user interface which allows the user to immediately make use of fMRI data for multiple analyses. The application visualization system (AVS) was chosen to provide a graphical environment for the tools. A series of AVS modules were created to allow the user to perform several processing and analysis tasks using the serial fMRI image data as a starting point. Modules were developed to provide t-test analysis and cross-correlation analysis, in which the user is able to select a suitable idealized driving function which can be interactively modified to suit the given fMRI protocol. Both time and frequency analyses are possible on each pixel in the images. In addition, several co- registration methods have been developed to resolve problems arising from patient motion.

SU‐E‐I‐57: CT Dose Metrics: What Are We Tracking

PURPOSE Recent guidance by The Joint Commission and CRCPD recommendations require establishing CT reference dose levels (RDLs) for clinical protocols and recording CT dose metrics in the patients medical record. This presentation addresses which dose values in the CT report should be recorded for the purposes of monitoring patient dose and determining RDLs effectively. METHODS CT dose reports are commonly recorded in the PACS as screen captures, although structured reporting is becoming available on current CT scanners and PACS systems. The goal is to obtain data that correctly reflects the patients dose, but the dose information captured is not standardized across vendors and can be difficult to compare. Multi-phase studies, deviations from established protocols and dynamic scanning present problems when recording numbers to establish RDLs because of the lack of information on the anatomy scanned. The cumulative DLP and CTDIvol manually entered by radiologic technologists into the electronic medical record were compared with more detailed dose metrics compiled from PACS images. RESULTS Analysis of this data showed that simple cumulative metrics are a poor indicator of patient dose. Major problems are 1) the inclusion of dynamic scan doses associated with bolus tracking, which can skew protocol CTDIvol values by a factor of up to 20, and 2) add-on scans of non-overlapping anatomy which can inaccurately increase apparent patient dose. CONCLUSIONS Recording CTDIvol to monitor patient doses is not straightforward, since details of the actual anatomy scanned are lacking without image-based review. More granular dose reporting which identifies individual acquisitions is required; however, current RIS systems do not provide the flexibility necessary to capture all this information.

SU‐E‐I‐82: CT Protocol Translation in a Multi‐Vendor, Multi‐Hospital Environment

Purpose: To review issues involved with designing CT protocols for achieving consistent standards in a multi‐vendor and multi‐institutional enterprise.Methods: Achieving consistent CT protocols is complicated by a variety of factors. Even in a given institution, CTs from different vendors complicate standardizing protocols. An approach based on uniform CTDI values for exam types may meet with resistance due to individual radiologistimage preference. The situation is further complicated in multi‐institutional settings where patient demographics, radiologist, and clinician cultures can vary widely. At UT Southwestern, there are three major institutions using CT equipment from different vendors and servicing distinct patient population groups. A childrens hospital, a teaching county hospital, and a university hospital are serviced by a common radiology group. Recent media attention to CTdose, and recommendations by the Conference of Radiation Control Program Directors (CRCPD) have spurred State regulatory bodies to draft requirements for dosemanagement. Examples are given outlining methods to achieve consistent protocols across our facilities, based on experience at UT Southwestern.Results: The approach at UT Southwestern was based on CRCPD recommendations. Further guidance was found in ACR, the Image Gently, and Image Wisely campaigns. A specific result, is given of translating a set of pediatric protocols from the childrens hospital to adult facilities employing CTs from different vendors Conclusions: CT protocols can be standardized in multi‐vendor and multi‐ institutional environments. A critical aspect of the process is buy‐in from the radiology staff and further support from management.

SU‐E‐I‐83: Filling the Gap: Using Detailed Machine Parameters to Refine Skin Dose Calculations for Fluoroscopic Sentinel Events

Purpose: To examine the role that detailed machine logs, supplementary procedural documentation and vendor‐generated technique and dosimetry information can play in refining calculation of peak skin dose for sentinel event investigations.Methods: Vendor‐specific machine logs, skin‐dose estimations, and procedural observations can supplement the fluoroscopic times and air kerma values that all fluoroscopic machines are required to report since 2006. Information available from vendors varies considerably, and in some cases specific application products must be purchased to access this information. Information embodied may include table position, c‐arm geometry, collimation, individual run and fluoro acquisition dosimetry, technique factors (mA, kVp, pulse configuration), mode of operation and other data. Peak skin dose estimates based on HIS/RIS data and DICOM image headers were compared to calculations supplemented by the detailed machine logs and vendor dosimetry estimates. Skin dose maps were generated from air kerma readings and from the DICOM information associated with each run. Assumptions are necessary in this approach to apportion the fluoroscopic contribution, which can be 80% of the air kerma. Corresponding skin dose maps were generated with inclusion of more detailed machine log data and the resulting peak skin dose location and magnitudes were compared.Results: Significant deviations were observed between peak skin dose calculations based on DICOM information alone with attendant assumptions versus those obtained with more detailed machine log data. Detailed logs provide complementary information that replaces assumptions on fluoroscopic dose contributions with more reliable values. Conclusions: Additional information from vendors logs and dose‐ estimates and from other sources can increase the confidence in skin‐dose calculations, but the specific assumptions made by both the physicist and the vendor in making such estimates must be carefully examined. The comparison enables the stand‐alone assumptions to be validated and also allows evaluation of vendor dosimetry estimates.

How Will You Need Me, How Will You Read Me, When I'm 64 (or More!)?: Volume Computed Tomographic Scanning and Information Overload in the Emergency Department

Computed tomographic (CT) scanning technology now employs up to 320 detector rows of 0.5-mm width and allows rapid acquisition of isotropic volume datasets over the entire body. Data from a single CT acquisition can be reconstructed into image series that would formerly have required multiple acquisitions. Small isotropic voxels permit scan parameters to be general while reconstruction algorithms remain specific to anatomy. While this results in more efficient operation in the Emergency Department, it necessitates new ways of displaying, interpreting, and archiving the information. Critical decisions include how much of the patient to scan and how to time contrast injections when imaging multiple organs. These choices must be made in light of dose considerations to the patient and the general population of patients. The technical basis of high-density CT scanning is discussed, including detector configurations and reconstruction techniques. Volumetric scanning in the Emergency Department can improve patient care but requires a change of technical habits.

Image enhancement method for digital mammography

Purpose: To evaluate in clinical use a practical iterative deconvolution method to enhance contrast and image resolution in digital breast tomosynthesis. A novel rapidly converging, iterative deconvolution algorithm for improving the quantitative accuracy of previously reconstructed breast images by commercial breast tomosynthesis system is demonstrated. Materials and Methods: The method was tested on phantoms and clinical breast imaging data. Data acquisition was performed on a commercial Hologic Selenia Dimensions digital breast tomosynthesis system. The method was applied to patient breast images previously processed with Hologic Selenia conventional and C-View software to determine improvements in resolution and contrast to noise ratio. Results: In all of the phantom and patients’ breast studies the post-processed images proved to have higher resolution and contrast as compared with images reconstructed by Hologic methods. In general, the values of CNR reached a plateau at around 8 iterations with an average improvement factor of about 1.8 for processed Hologic Selenia images. Improvements in image resolution after the application of the method are also demonstrated. Conclusions: A rapidly converging, iterative deconvolution algorithm with a novel resolution subsets-based approach that operates on patient DICOM images has been used for quantitative improvement in digital breast tomosynthesis. The method can be applied to clinical breast images to improve image quality to diagnostically acceptable levels and will be crucial in order to facilitate diagnosis of tumor progression at the earliest stages. The method can be considered as an extended blind deblurring (or Richardson-Lucy like) algorithm with multiple resolution levels

SU‐E‐I‐08: Do CTDI Measurements Approximate Peak Skin Dose for Wide‐Beam Volumetric Scans?

PURPOSE To investigate the relationship between peak skin dose and CTDI measurements for wide-beam volumetric (stationary table) CT scanning. METHODS Air-kerma (AK) measurements were performed in head and body CTDI phantoms using conventional CTDI, extended CTDI (CTDIe), and AAPM TG-111 protocols. These measurements were compared to skin dose estimates obtained using a small volume (0.1 ml) ion chamber (IC) mounted on the anterior surface of the phantoms. Measurements were made on a volumetric CT scanner (Toshiba Aquilion ONE) for collimations of 40, 80, 120 and 160 mm and at kVp settings of 80, 100, and 120. Anterior and lateral surface dose measurements were also made on anthropomorphic phantoms at the same fixed techniques. RESULTS In the CTDI body phantom, peripheral CTDIe nearly equals surface dose while CTDIevol underestimates surface dose by 10-30% over the collimation range. In the CTDI head phantom, either the peripheral or the volume CTDIe values fall within approximately 5% of the surface dose for collimations greater than 80 mm. At smaller collimation, CTDIe values overestimate surface dose in the head phantom. TG-111 f(0) measurements in the anterior peripheral location slightly overestimate anterior surface dose measurement results for both head and body CTDI phantoms. Surface measurements on the anthropomorphic phantoms exhibit variations between anterior and lateral locations, with lateral doses being smaller. CONCLUSION Values derived from CTDIe measurements are useful indicators of peak skin dose for cylindrical phantoms at beam widths in excess of 80 mm. In patients, geometrical correction factors similar to the Size Specific Dose Estimate (SSDE) methodology might be used to account for actual body habitus. Toshiba America Medical Systems is supporting an associated research project on the scanner used for this work. Dr Di Zhang is an employee of Toshiba America Medical Systems.