Volume 36, Issue 6, June 2009
Index of content:
- Imaging Continuing Education Course: Room 303A
- CE ‐ Imaging: MRI II
36(2009); http://dx.doi.org/10.1118/1.3182194View Description Hide Description
The MR Subcommittee of the AAPM Imaging Physics Committee (IPC) has recently completed a revision of the previous AAPM TG1 and TG6 reports on MR acceptance testing and quality assurance. The report of the MR Subcommittee has been approved by the IPC and will be available electronically (http://www.aapm.org/pubs/reports/). In this session of the MR continuing education course, the contents of the report will be presented. Recommendations regarding testing of magnetic and radiofrequency(RF) shielding will be followed by recommendations on specific acceptance tests of magnetic field homogeneity, the RF subsystem (calibration, stability), the gradient subsystem (calibration,eddy current compensation), combined subsystems (slice thickness and spacing), global system performance (SNR, uniformity, high and low contrast resolution), and advanced tests (MRspectroscopy, echo planar imaging).
1. Understand the requirements for MR site and system acceptance tests.
2. Review recommended MR site and system acceptance testing procedures, including phantom selection, data acquisition,data analysis, and reporting.
3. Review recommended action criteria for both standard imaging options and advanced imaging and spectroscopy options.
- CE ‐ Imaging: Breast Imaging I
36(2009); http://dx.doi.org/10.1118/1.3182201View Description Hide Description
Full Field Digital Mammography (FFDM) systems are fast becoming popular and replacing conventional film‐screen mammographysystems. FFDM systems use a digital detector instead of screen‐film to capture the image of the breast. Several FFDM systems based on different digital detector design and materials are currently available. Some systems are characterized as direct conversion detectors and some are based on indirect conversion process. The digital detectors can be characterized by image quality metrics such as detector quantum efficiency (DQE) and modulation transfer function(MTF).
In this lecture, the physics and technology of the digital detectors used in FFDM will be discussed as well as the advantages and applications arising due to the availability of these systems will be presented. The most recent commercially available systems will also be discussed.
1. Understand the physics of digital detector technology
2. Understand the image quality metrics such as DQE and MTF
3. Recognize that vendors use varying detector technology in FFDM systems
4. Appreciate the advantages and disadvantages of digital mammographysystems
- CE ‐ Imaging: Computed Tomography II
36(2009); http://dx.doi.org/10.1118/1.3182309View Description Hide Description
This Continuing Education session surveys the principles of 3D reconstruction,image quality, radiation dose, and applications of C‐arm cone‐beam CT. The availability of such systems has grown over the past several years, with applications including neurovascular and cardiovascular imaging in image‐guided interventions and surgery. Some systems employ conventional x‐ray image intensifiers, with corresponding limitations in image quality (i.e., imaging of high‐contrast structures only). More recent systems incorporating a flat‐panel detector in the imaging chain demonstrate increased field of view, higher 3D spatial resolution, improved noise characteristics, and the capability to visualize soft‐tissue structures. The basic principles of cone‐beam CTimage reconstruction are reviewed (Feldkamp algorithm) in comparison to conventional fan‐beam filtered backprojection. The influence of image artifacts most relevant to C‐arm cone‐beam CT are reviewed — in particular, x‐ray scatter, object truncation, and the “cone‐beam” artifact. The factors governing 3D image quality are explained, with emphasis on the ability to image soft‐tissue structures, and issues of radiation dose characterization are discussed. The spectrum of various C‐arm cone‐beam CTsystems is discussed in relation to primary applications in image‐guided interventions. Emphasis throughout is in regard to factors most relevant to the practicing medical physicists.
Learning Objectives: Attendees will gain practical understanding of:
1. Basic principles of 3D cone‐beam CTreconstruction
2. Image quality and artifacts most relevant to cone‐beam CT
3. Spectrum of systems and applications of C‐arm cone‐beam CTI
- CE ‐ Imaging: Breast Imaging II
36(2009); http://dx.doi.org/10.1118/1.3182315View Description Hide Description
Full Field Digital Mammography (FFDM) systems are rapidly gaining in popularity and are replacing conventional film‐screen mammography (FSM) systems in breast centers throughout the country. Radiolgists are faced with unique challenges brought about by this transition of technology.
In this lecture, the utility of full field digital mammography in clinical practice will be presented. Some of the challenges faced by radiologists who have transitioned from film screen mammography to digital mammography will also be discussed, and case examples illustrating the utility of FFDM will be presented. The clinical utility of computer‐aided detection (CAD) software packages will also be addressed.
1. Understand the clinical impact that full‐field digital mammography has had on the daily practice of breast imaging.
2. Recognize the advantages and disadvantages of FFDM systems.
3. Understand some of the challenges that breast imagers face when transitioning from FSM to FFDM systems.
4. Understand how computer‐aided detection (CAD) systems are used in clinical practice.
- CE ‐ Imaging: MRI III
36(2009); http://dx.doi.org/10.1118/1.3182448View Description Hide Description
Dynamic contrast enhanced (DCE) MR imaging is emerging as a promising biomarker for therapy assessment. While initial results from research groups are promising, a significant gap exists between preliminary research studies and practical utilization. In addition to variations in data acquired from different image acquisition techniques, a large variety of pharmacokinetic models have been explored from which to derive quantitative metrics. Examples of such models include those from Patlack, Toft, and Elizabeth, with a number of others in use in various research groups. These models have various levels of complexity, which in general is inversely related to the robustness with which the models perform on imaging data. Furthermore, the selection of an optimal pharmacokinetic model may be highly dependent on the tissue or organ being investigated. Currently, a national effort is underway to help standardize the extraction of physiological parameters from DCE‐MRI and related pharmacokinetic models. This talk explores these issues, comparing various models and their performance, and provides an overview of the areas that need consideration prior to widespread adoption of DCE‐MRI derived model parameters as assessment tools.
1. Understand the strengths and weaknesses of commonly used pharmacokinetic models
2. Understand the influence of image acquisition parameters and image quality on derived quantitative metrics
3. Provide examples of clinical applications
- CE ‐ Imaging: Breast Imaging III
36(2009); http://dx.doi.org/10.1118/1.3182454View Description Hide Description
Stereotactic Breast Biopsy (SBB) often seems to be the poor stepchild of the breast health family. This is exemplified by the fact that the number of units in the voluntary American College of Radiology SBB Accreditation Program measures in the hundreds, compared to over 13,000 units in the Mammography Accreditation Program. However, SBB holds its place as a vital player in the diagnosis of breast cancer. As such, the image quality and performance demands of SBB systems are great. Any object of interest seen on a mammogram must be visible in the SBB image, or the biopsy cannot take place. The purpose of this presentation is to provide an update on Stereotactic Breast Biopsy systems and the clinical demands placed on them. Techniques for testing these systems will be presented. Features of various systems will be discussed. Information regarding the ACR SBBAP will also be presented. Education objectives: 1) To become familiar with the approaches to Stereotactic Breast Biopsy. 2) To gain an understanding of the clinical requirements for these systems. 3) To review quality control requirements and methods for clinical SBB systems.
- CE ‐ Imaging: Computed Tomography III
36(2009); http://dx.doi.org/10.1118/1.3182591View Description Hide Description
Accreditation of computed tomography systems is increasingly important as reimbursements become tied to the successful achievement and maintenance of accreditation status. This presentation reviews the technical requirements for the medical physicist who will be in charge of performing quality assurance and ACR accreditation testing of a CT scanner. These duties include establishing schedules for routine quality assurancetesting, performing pre‐submission and annual testing, and performing testing for the ACR submission. All of these are reviewed from a practical standpoint of performing the required studies in an efficient manner with appropriate record keeping and documentation.
Learning Objectives: Attendees will gain understanding of the
1. Requirements for the physics testing for ACR accreditation
2. Practical aspects of testingCT systems
3. Performance of annual surveillance testing and pre‐application testing
4. Establishment of routine quality assurance protocols and record keeping
- CE ‐ Imaging: MRI IV
36(2009); http://dx.doi.org/10.1118/1.3182598View Description Hide Description
The use of the self‐diffusion characteristics of water to generate imagecontrast for magnetic resonance imaging(MRI) can provide a wealth of information about tissuemicrostructure.Diffusionimaging has demonstrated sensitivity to pathology in structured tissues (e.g., white matter, cardiac muscle fiber, kidney), where the structure may be altered. Additionally, the relative volume of water between intra‐ and extra‐cellular compartments, as well as the permeability of tissue membranes dividing the compartments, may be affected by certain diseases. Cancer, in particular, affects water diffusivity in a number of ways. In tumor regions where a high density of cells exists, the diffusion of extra‐cellular water can be more restricted than healthy tissue. In regions where the tumor has become necrotic or cystic, diffusion is less restricted. Tissue structure may not be affected equally in all directions. Invasiveness of cancer into neural fibers in the brain, or their preservation and displacement around a tumor, will exhibit differences in diffusion magnitude as well as direction of restriction. Finally, therapeutic intervention (radiation therapy or chemotherapy) of cancer can be monitored using diffusion techniques, where increases in diffusion within a tumor may suggest the efficacy of treatment.
This presentation will provide a survey of different diffusionMRI techniques, focusing in particular on when they may be helpful in the diagnosis and treatment of cancer.
1. To describe how biological changes in tissue correlate with diffusive behavior of water.
2. To provide a simple picture of cancer and the different ways in which it can alter cellular diffusioncharacteristics.
3. To give an overview of the different diffusionimaging techniques in MRI: How do they work? What information do they provide? Under what contexts are they important in the diagnosis of cancer?