N Hangiandreou

The calibration of experimental self-developing Gafchromic® HXR film for the measurement of radiation dose in computed tomography

A prototype, self-developing Gafchromic HXR film has sensitivity an order of magnitude larger than that of the commercially available Gafchromic XR film used in interventional radiological applications. The higher sensitivity of the HXR film allows the possibility of acquisition of high-resolution calibrated dose profiles within the diagnostic range of exposure levels, below 10 R (87.7 mGy). We employed a commercially available, optical flatbed scanner for digitization of the film and image analysis software to determine the response of the HXR films to ionizing radiation. Spatial uniformity and temporal repeatability of the flatbed scanner were determined and used in optimization of the digitization protocol. The HXR film postexposure density growth and sensitivity to ambient light were determined using multiple scans of two simultaneously exposed sheets, one stored in light-tight conditions and the other continuously illuminated with white light. A calibrated step wedge of the HXR film was obtained by simultaneous irradiation of a portion of a film strip and a calibrated ionization chamber using a radiographic x-ray tube with beam characteristics matched to a typical CT scanner (8 mm Al HVL, 120 kVp). Repeated digitization of the calibration film was used to determine the precision of the film response measurements. The precision, as measured by the standard deviation of multiple measurements, was better than 1% over the full dynamic range of film response. This precision was measured using exposures ranging from 0.5 to 12 R (4.4 to 105.3 mGy). This exposure range is highly relevant to x-ray computed tomography. Preliminary radiation dose profiles demonstrate the utility of this technique.

An evaluation of the signal and noise characteristics of four CCD-based film digitizers

Film digitizers are common devices in radiology departments involved with picture archive and communication systems (PACS) and teleradiology. In this paper, we studied the performance of film digitizers based on charge-coupled device detectors (CCD digitizers), and compared this with the performance of a laser digitizer (the de facto standard). Our focus was on the assessment of signal, noise and useful optical density range performance. A function (L* delta D) derived from the Rose model was used to evaluate these parameters in absolute terms, based their predicted ability to detect objects of specific size and optical density difference with respect to background. We studied CCD digitizers from four different vendors and found that none was able to reliably operate up to the maximum density of 3.0 required to digitize plain radiographs, while the laser digitizer was capable of this task. Our analysis also indicated that two of the four CCD digitizers were adequate for digitizing laser-printed cross-sectional images in certain cases. Finally, our analysis indicated that digitization of SMPTE pattern films along with visual assessment of the 5% and 95% contrast patches was not sufficient for determining the utility of film digitizers for clinical tasks. Computation of the L* delta D function provides a useful means of assessing the performance of film digitizers (e.g., for acceptance testing and quality control), and this technique may be adaptable for evaluation of other digital imaging modalities.

Evaluation of mineral oil as an acoustic coupling medium in clinical MRgFUS

We empirically evaluate mineral oil as an alternative to the mixture of de-gassed water and ultrasound gel, which is currently used as an acoustic coupling medium in clinical magnetic resonance guided focused ultrasound (MRgFUS) treatments. The tests were performed on an ExAblate 2000 MRgFUS system (InSightec Inc., Haifa, Israel) using a clinical patient set-up. Acoustic reflections, treatment temperatures, sonication spot dimensions and position with respect to target location were measured, using both coupling media, in repeated sonications in a tissue mimicking gel phantom. In comparison with the water-gel mix, strengths of acoustic reflections from coupling layers prepared with mineral oil were on average 39% lower and the difference was found to be statistically significant (p = 3.3 x 10(-8)). The treatment temperatures were found to be statistically equivalent for both coupling media, although temperatures corresponding to mineral oil tended to be somewhat higher (on average 1.9 degrees C) and their standard deviations were reduced by about 1 degrees C. Measurements of sonication spot dimensions and positions with respect to target location did not reveal systematic differences. We conclude that mineral oil may be used as an effective non-evaporating acoustic coupling medium for clinical MRgFUS treatments.

Development of an MRI fiducial marker prototype for automated MR-US fusion of abdominal images

External MRI fiducial marker devices are expected to facilitate robust, accurate, and efficient image fusion between MRI and other modalities. Automating of this process requires careful selection of a suitable marker size and material visible across a variety of pulse sequences, design of an appropriate fiducial device, and a robust segmentation algorithm. A set of routine clinical abdominal MRI pulse sequences was used to image a variety of marker materials and range of marker sizes. The most successfully detected marker was 12.7 mm diameter cylindrical reservoir filled with 1 g/L copper sulfate solution. A fiducial device was designed and fabricated from four such markers arranged in a tetrahedral orientation. MRI examinations were performed with the device attached to phantom and a volunteer, and custom developed algorithm was used to detect and segment the individual markers. The individual markers were accurately segmented in all sequences for both the phantom and volunteer. The measured intra-marker spacings matched well with the dimensions of the fiducial device. The average deviations from the actual physical spacings were 0.45± 0.40 mm and 0.52 ± 0.36 mm for the phantom and the volunteer data, respectively. These preliminary results suggest that this general fiducial design and detection algorithm could be used for MRI multimodality fusion applications.

TU-C-18C-01: Medical Physics 1.0 to 2.0: Introduction and Panel Discussion

Medical Physics 2.0, a new frontier in clinical imaging physics: Diagnostic imaging has always been a technological highlight of modern medicine. Imaging systems, with their ever-expanding advancement in terms of technology and application, increasingly require skilled expertise to understand the delicacy of their operation, monitor their performance, design their effective use, and ensure their overall quality and safety, scientifically and in quantitative terms. Physicists can play a crucial role in that process. But that role has largely remained a severely untapped resource. Many imaging centers fail to appreciate this potential, with medical physics groups either nonexistent or highly understaffed and their services poorly integrated into the patient care process. As a field, we have yet to define and enact how the clinical physicist can engage as an active, effective, and integral member of the clinical team, and how the services that she/he provides can be financially accounted for. Physicists do and will always contribute to research and development. However, their indispensible contribution to clinical imaging operations is something that has not been adequately established. That, in conjunction with new realities of healthcare practice, indicates a growing need to establish an updated approach to clinical medical imaging physics. This presentation aims to describe a vision as how clinical imaging physics can expand beyond traditional insular models of inspection and acceptance testing, oriented toward compliance, towards team-based models of operational engagement addressing topics such as new non-classical challenges of new technologies, quantitative imaging, and operational optimization. The Medical Physics 2.0 paradigm extends clinical medical physics from isolated characterization of inherent properties of the equipment to effective use of the equipment and to retrospective evaluation of clinical performance. This is an existential transition of the field that speaks to the new paradigms of value-based and evidence-based medicine, comparative effectiveness, and meaningful use. The panel discussion that follows includes prominent practitioners, thinkers, and leaders that would lead the discussion on how Medical Physics 2.0 can be actualized. Topics of discussion will include the administrative, financial, regulatory, and accreditation requirements of the new paradigm, effective models of practice, and the steps that we need to take to make MP 2.0 a reality. LEARNING OBJECTIVES 1. To understand the new paradigm of clinical medical physics practice extending from traditional insular models of compliance towards teambased models of operational engagement. 2. To understand how clinical physics can most effectively contribute to clinical care. 3. Learn to identify strengths and weaknesses in studies designed to measure the effect of low doses of ionizing radiation 4. To recognize the impediments to Medical Physics 2.0 paradigm.

TU-A-9A-02: Analysis of Variations in Clinical Doppler Ultrasound Peak Velocity Measurements

PURPOSE Doppler ultrasound (US) peak velocity (Vmax) measurements show considerable variations due to intrinsic spectral broadening with different scanning techniques, machines and manufacturers. We developed a semi-automated Vmax estimation method and used this method to investigate the performance of a US system for clinical Doppler Vmax measurement. METHODS Semi-automated Vmax is defined as the velocity at which the computed mean spectral profile falls to within 1 background standard deviation of the background mean. GE LOGIQ E9 system with 9L and ML6-15 probes were studied with steady flow (5.3 - 12.5 ml/s) in a Gammex OPTIMIZER 1425A phantom. All Doppler spectra were acquired by 1 operator at the distal end of 5 mm angular tube using a modified clinical carotid artery protocol. Repeatability and variation of Vmax to scanning parameters and probes were analyzed and reported as percentage, i.e. (max-min)/mean. RESULTS Vmax estimation had good repeatability (3.1% over 6 days for 9L, and 3.6% for ML6-15). For 9L probe, varying gain, compression, scale, SV depth and length, and frequency had minimal impact on Vmax (all variations less than 4.0%). Beam steering had slightly higher influence (largest variations across flow rates were 4.9% for 9L and 6.9% for ML6-15). For both probes, Doppler angle had the greatest effect on Vmax. Percentage increase of Vmax was largely independent of actual flow rates. For Doppler angle varied from 30 to 60°, Vmax increased 24% for 9L, and 20% for ML6-15. Vmax measured by ML6-15 were lower than that by 9L at each Doppler angle with differences less than 5%. CONCLUSION The proposed Vmax estimation method is shown to be a useful tool to evaluate clinical Doppler US system performance. For the tested system and probes, Doppler angle had largest impact in measured Vmax.

TU-A-18C-01: ACR Accreditation Updates in CT, Ultrasound, Mammography and MRI

A goal of an imaging accreditation program is to ensure adequate image quality, verify appropriate staff qualifications, and to assure patient and personnel safety. Currently, more than 35,000 facilities in 10 modalities have been accredited by the American College of Radiology (ACR), making the ACR program one of the most prolific accreditation options in the U.S. In addition, the ACR is one of the accepted accreditations required by some state laws, CMS/MIPPA insurance and others. Familiarity with the ACR accreditation process is therefore essential to clinical diagnostic medical physicists. Maintaining sufficient knowledge of the ACR program must include keeping up-to-date as the various modality requirements are refined to better serve the goals of the program and to accommodate newer technologies and practices. This session consists of presentations from authorities in four ACR accreditation modality programs, including magnetic resonance imaging, mammography, ultrasound, and computed tomography. Each speaker will discuss the general components of the modality program and address any recent changes to the requirements. LEARNING OBJECTIVES 1. To understand the requirements of the ACR MR accreditation program. The discussion will include accreditation of whole-body general purpose magnets, dedicated extremity systems well as breast MRI accreditation. Anticipated updates to the ACR MRI Quality Control Manual will also be reviewed. 2. To understand the current ACR MAP Accreditation requirement and present the concepts and structure of the forthcoming ACR Digital Mammography QC Manual and Program. 3. To understand the new requirements of the ACR ultrasound accreditation program, and roles the physicist can play in annual equipment surveys and setting up and supervising the routine QC program. 4. To understand the requirements of the ACR CT accreditation program, including updates to the QC manual as well as updates through the FAQ process.

WE‐A‐103‐01: Ultrasound

Ultrasound quality control (QC) testing is often over-looked in ultrasound imaging practice because there are few regulations requiring regular QC of these systems. Many sites rely on the manufacturers preventive maintenance program to ensure these systems are functioning optimally. However, the regulatory climate is changing, placing emphasis on safe and effective imaging practice. Regular QC testing of ultrasound equipment is a valuable tool that helps ensure proper function and good image quality in ultrasound imaging. This two-hour session is organized in two parts. The first hour will cover the basic concepts of ultrasound performance measurement, including the tests that are recommended for acceptance and annual testing as well as routine QC, the rationale for these tests, and specific testing methods. It will also include what the physicist needs to know about ultrasound accreditation. The next hour includes two presentations related to quantitative assessment of ultrasound QC. First presented is the work of the AAPM working group on Quantitative B-mode Ultrasound QC Test Development. This group has designed software intended to aid in the evaluation of transducer element condition. The second presentation will demonstrate use of a user-friendly automation software, developed at the University of Wisconsin, for periodic rapid quality assurance (QA or QC) using the tissue-mimicking conical window phantom described last year. The phantom has been designed specifically for determination of three basic parameters. A method for organizing an electronic filing system for paperless recording of results will also be described. LEARNING OBJECTIVES 1. Understand what constitutes an effective ultrasound QC program. 2. Achieve familiarity with common ultrasound QC test methods and phantoms. 3. Understand what the physicist needs to know about ultrasound program accreditation. 4. Learn about a public software tool being developed by the AAPM Ultrasound Subcommittee to detect and assess transducer uniformity artifacts. 5. Learn about a user-friendly automation software tool to address the most-recommended ultrasound QC tests.

SU‐E‐I‐68: Preliminary Evaluation of Potential MRI Contrast Materials for the Purpose of MR‐Ultrasound Fusion Application in the Abdomen

PURPOSE To evaluate a variety of materials that might serve as fiducial markers for abdominal MRI-ultrasound fusion applications. METHODS Two experiments were performed: (1) in a phantom, a broad set of candidate materials were evaluated based on visibility in spin echo T1 and T2, and gradient echo T1 and T2* MRI pulse sequences; (2) the leading candidates were evaluated using standard clinical abdominal pulse sequences, both in a phantom and volunteer. Experiment 1 evaluated: two commercial fiducial MRI markers (IZI Medical Products and Beekley Medical); vitamin E and fish oil capsules; water; and copper sulfate solution. Experiment 2 evaluated fish oil capsules and copper sulfate solution. In experiment 2, ultrasound coupling gel was also evaluated. Liquids were poured in wells drilled in a plexiglass base. All scanning was performed with a clinical 1.5T GE Signa Excite scanner. For each pulse sequence, maximum intensity projection images (MIPs) were formed, after removing the phantom signals. Visibility was evaluated by rank ordering signal magnitude in the MIPs. RESULTS In experiment 1, copper sulfate solution and fish oil were superior to the other materials. In experiment 2, ultrasound gel and copper sulfate solution were clearly superior to the other materials, and were easily seen in the all of the phantom and volunteer images. CONCLUSION Based on these preliminary experiments, ultrasound gel and copper sulfate solution appear to be the most promising fiducial marker materials for MRI-ultrasound fusion applications in the abdomen.

MO‐D‐218‐03: ACR Ultrasound Practice Accreditation and Technical Standard for Ultrasound Performance Monitoring

The first part of this presentation will provide an overview of the American College of Radiology (ACR) Technical Standard for Diagnostic Medical Physics Performance Monitoring of Real Time Ultrasound Equipment, as well as the ACR Accreditation requirements for general and breast ultrasound practices. The second part of the will discuss practical aspects of implementing QC programs that satisfy the requirements of the ACR practice accreditation programs, including consideration of personnel roles, and performance testing schedules, specific methods, and available tools. LEARNING OBJECTIVES 1. Understand the ACR Technical Standard for Diagnostic Medical Physics Performance Monitoring of Real Time Ultrasound Equipment, and the QC requirements of the ACR Ultrasound and Breast Ultrasound Practice Accreditation Programs 2. Be able to implement ultrasound QC programs in keeping with these documents.