Volume 34, Issue 6, June 2007
Index of content:
- Imaging Continuing Education Course: Room L100E
- CE‐Imaging: The Physics and Technology of Magnetic Resonance Imaging — I
MO‐A‐L100E‐01: Parallel Imaging: Techniques, Quality Control, and Applications (Preview of TG118 Repo34(2007); http://dx.doi.org/10.1118/1.2761187View Description Hide Description
Task Group ♯118 of the AAPM was established to describe the basis of parallel magnetic resonance imaging (pMRI) and its applications to the Medical Physics community. This presentation reviews the aspects of parallel imaging methods that have led to this technology becoming important clinically. The signature enhancement attributable to pMRI is faster MRimage acquisition which leads to decreased motion artifact, reduced breath‐hold time, shorter durations of exams or more series acquired per exam. Increased flexibility is also achieved since parallel imaging has distinct advantages for limiting specific absorption rate (SAR) at higher magnetic field strengths.
There are currently two general approaches to pMRI; one based on image‐spacereconstruction and the other on k‐space based methods. Details of the design of RF coils, or the entire RF systems, for improving imaging performance in pMRI will be surveyed. Additional benefits may be derived from the use of pMRI in balanced gradient echo imaging, fast spin echo imaging, dynamic MRI, BOLD contrast MRI and diffusion MRI. In addition, the image quality trade‐offs in pMRI will be considered with particular focus on the different ways that signal and noise are handled in pMRI image reconstruction.
Finally advanced results, which will likely lead to continuing improvements in pMRI technology, will be discussed. In summary, this presentation will provide practical guidance and assistance for the practicing medical physicist so that pMRI may be more readily applied and understood within the clinical environment.
By the end of this presentation the attendee should:
1. understand the basic concept of parallel imaging and how it can be used to reduce the acquisition time of MRimages.
2. recognize in which clinical protocols the use of parallel imaging methods is most advantageous and what benefits are bestowed on each.
3. be aware of the image quality trade‐offs involved in implementing pMRI and
4. understand the new image artifacts inherent with this approach.
- CE Series: Radiation Safety and Risk Management — I
MO‐B‐L100E: Magnitude of Medical Radiation Exposures to US population: Preliminary results from NCRP Scientific Committee 6‐234(2007); http://dx.doi.org/10.1118/1.2761199View Description Hide Description
National Council of Radiation of Protection formed Scientific Committee 6.2 to work on the estimation of radiation exposure to the US population from all sources. The intended goal of the Committee is to update the NCRP report 93 published in 1987. One sub group of the sub committee was assigned with the medical exposure. The medical sub committee comprised of medical physicists, physicians, and other health physics experts.
The subcommittee examined variety of data sources including commercial surveys, Medicare, Veterans Administration and insurance carrier data. Radiation exposure to the US population from medical exposures was then estimated based on the number of medical procedures grouped by modality and body parts and the radiationdoses associated with each procedure. The modality groups were CT, nuclear medicine,radiography, general and interventional fluoroscopy, dental radiography, bone‐densitometry and radiation therapy.
According to the preliminary results, the medicalradiation exposure to US population has increased by nearly 6 times compared to the previous NCRP publication (NCRP 93). The conventional pie‐chart indicating 3 mSv from background radiation and 0.6 mSv from man‐made (medical) exposure will undergo major shape change as these preliminary results are finalized. The largest contributor to the collective dose to US population is seen with CT and Nuclear Medicine.CT scanning has increased nearly 10–11% annually in the US in the past two decade. The number of CT procedures has increased from 3 million CT scans in 1980 to more than 62 million CT scans in 2006. Similarly, the nuclear cardiac procedures have increased significantly in the last two decades.
The purpose of this talk is to provide an update on the results from the medical patient exposure subcommittee and to discuss the details on how the results were derived.
1. To learn about the magnitude of medicalradiation exposure to US population.
2. To familiarize with the types and distribution of medical imaging procedures in US.
3. To understand methods used in computing the radiation exposures to US population.
- CE‐Imaging: The Physics and Technology of Magnetic Resonance Imaging — II
34(2007); http://dx.doi.org/10.1118/1.2761300View Description Hide Description
The American College of Radiology MRI Accreditation Program has been active since 1996. As of November 2006, almost 4400 facilities and over 5900 individual MR units had been accredited since the initiation of the program. Until recently, there have been few changes to the accreditation requirements since the program was initiated. However, the ACR recently expanded the original Whole Body MRI Accreditation Program to include 3T systems and very recently announced a CardiacMRI Accreditation Module. Additional modules, such as a Breast MRI Accreditation Module, are under development. In addition, the MRIQuality Control Manual, first printed in 2001 and revised, with minor changes, in 2004, is currently under revision.
This continuing education course will review the current status and requirements of the ACR Whole Body MRI Accreditation Program, the requirements for and issues related to 3T system accreditation, and the recently released CardiacMRI Accreditation Module. In addition, this course will focus on the expanding roles of medical physicists outside of the conventional ACR MR Accreditation Program involvement.
1. Review of the current ACR Whole Body MRI Accreditation Program requirements and current program statistics.
2. Review the recent modifications of the ACR MRI Accreditation Program, including the 3T scanner requirements as well as the requirements of the new CardiacMRI Accreditation Module.
3. Review the status of other MR initiatives that have been announced by the ACR.
4. Outline the expanding role of the medical physicist in MR quality assurance and accreditation.
- CE Series: Radiation Safety and Risk Management — II
TU‐B‐L100E‐01: Medical Response Planning for Nuclear/Radiological Emergencies: Roles of the Medical Physicist34(2007); http://dx.doi.org/10.1118/1.2761313View Description Hide Description
Medical health physicists working in a clinical setting have a number of key roles in preparing for and responding to a nuclear or radiological emergency, such as a terrorist attack involving a radiological dispersal device or an improvised nuclear device. Their first responsibility, of course, is to assist hospital administrators and facility managers in developing radiological emergency response plans for their facilities and train staff prior to an emergency. During a hospital's response to a nuclear or radiological emergency, medical health physicists may be asked to (1) evaluate the level of radiological contamination in or on incoming victims; (2) help the medical staff evaluate and understand the significance of the levels of radioactivity with which they are dealing; (3) orient responding medical staff with principles of dealing with radioactive contaminants; (4) provide guidance to staff on decontamination of patients and facilities; and (5) assist local public health authorities in monitoring people who are not injured but who have been or are concerned that they may have been exposed to radioactive materials or radiation as a result of the incident. Medical health physicists may also be called upon to communicate with staff, patients, and the media on radiological issues related to the event. The Centers for Disease Control and Prevention (CDC) is developing guidance in the areas of radiological population monitoring, handling contaminated fatalities, and using hospital equipment for emergency monitoring. CDC is also developing training and informationmaterials that may be useful to medical health physicists who are called upon to assist in developing facility response plans or respond to a nuclear or radiological incident.
1. Understand how the medical community will be involved in respond to a nuclear or radiological emergency.
2. Understand key roles that medical health physicists can play in preparing for and responding to such emergencies.
3. Learn what resources are available to assist medical health physicists and how these resources can be used.
- CE‐Imaging: The Physics and Technology of Magnetic Resonance Imaging — III
WE‐A‐L100E‐01: MR Data for Treatment Planning: Spatial Accuracy Issues, Protocol Optimization, and Applications (Preview of TG117 Report)34(2007); http://dx.doi.org/10.1118/1.2761462View Description Hide Description
Image‐guided therapies, including stereotactic radiosurgery, biopsy procedures, IMRT and image‐guided surgery are being used with increasing frequency. Although originally based primarily on CT data, image‐guided therapies now frequently use MR data alone, or in conjunction with CT data in the planning of or real‐time guidance of interventional procedures. Unlike CTimaging, the spatial accuracy of MRI data depends on both an appropriate QC program and the choice of appropriate image acquisition techniques. TG‐117 seeks to provide guidance regarding the optimization of imaging protocols and necessary QC procedures when MR systems are to be used to obtain data for procedures in which high spatial accuracy is critical.
This lecture will provide a preview of TG‐117, reviewing the physical bases for spatial distortions due to both system hardware and interaction of the system with the patient, describing methods for reducing or eliminating effects of distortion in MR imaging including protocol optimization and correction strategies, and presenting examples of QC tests for MR systems used to obtain data for procedures requiring high spatial accuracy.
1. Understand the physical bases for spatial distortions.
2. Understand image acquisition optimization and correction strategies for minimizing or eliminating effects of spatial distortions.
3. Understand issues related to QC testing for clinical applications requiring high spatial accuracy.
- CE Series: Medical Imaging Informatics — I
34(2007); http://dx.doi.org/10.1118/1.2761478View Description Hide Description
The development of the DICOM Standard is done through Working Groups of the DICOM Standards Committee. The Working Groups perform the majority of work on the extension of and corrections to the Standard. The ACR Committee on DICOM Standards, under the Commission on Medical Physics, has been established to provide a summary of the current activities and future directions of the DICOM Standards Committee. The extensions are made through development of Supplements and corrections are done through the Chance Proposal (CP) mechanism. In this presentation the procedures used to create the Standard will be reviewed and some of the most recent changes discussed.
Enhancements recently incorporated into the standard that have significance to medical physicists will be reviewed. These include:
WG04 (Compression) — JPEG 2000 Interactive Protocol.
WG21 (CT) — Enhanced CTImage Storage SOP Class, CTRadiation Dose Reporting.
WG16 (MR) — Multiframe MR Object.
WG17 (3D) — Segmentation Storage SOP Class, Deformable Spatial Registration Storage SOP Class.
New work items that have been approved that will lead to further enhancements in the near future are:
WG3 (NM) — Enhanced PET Image Storage SOP Class.
WG17 (3D) — Surface Segmentation Storage SOP Class.
WG15 (Digital Mammography) — Breast TomosynthesisImage Storage SOP Class.
WG7 (RT) — Enhanced RT Object.
1. Understand how DICOM Working Groups develop enhancements to the Standard.
2. Learn the significance of enhancements recently incorporated into the Standard.
3. Review new work being done to improve the Standard.
- CE‐Imaging: The Physics and Technolog of Magnetic Resonance Imaging — IV
34(2007); http://dx.doi.org/10.1118/1.2761607View Description Hide Description
- CE‐Imaging: The Physics and Technology of Ultrasound Imaging
34(2007); http://dx.doi.org/10.1118/1.2761623View Description Hide Description
Background:Ultrasound stimulated Vibro‐acoustography has been used to image tissues using the acoustic response of tissues to localized harmonic radiation pressure. The method provides high resolution and high dynamic range images of tissues. The parameter being imaged is a complex combination of scattering, attenuation, and nonlinearity. However specific use of harmonic or pulsed radiation pressure and subsequent measurement of the tissue response can be used to measure fundamental material properties of tissue. The measurement of shear wave dispersion can be used to estimate elastic shear moduli of tissue. Fundamental model free properties such as elastic storage and loss constants can also be measured.Methods:Ultrasound radiation pressure is used to induce free propagating shear waves. The measurableproperties of the shear waves are sensitive to only the material properties of the tissue under certain circumstances. A model relating the shear wave speed as a function of frequency is related to the elastic and viscous moduli within small regions of tissue. Results: Shear and elastic moduli in tissue are measured with high accuracy and precision given appropriate models of wave propagation within the geometry of the tissue. Conclusion: Careful use of shear wave propagation and subsequent measurements can provide fundamental measurements of tissue mechanical properties if models are accurate. An application of this method is the noninvasive measurement of liver stiffness as a surrogate for fibrosis.
1. Understand Shear Wavemoduli.
2. Understand Vibrometry.
3. Understand measurement of elasticity and viscosity with ultrasound.