Volume 35, Issue 6, June 2008
Index of content:
- SAMs Imaging Symposium: Room 332
CE‐Imaging: The Physics and Technology of Magnetic Resonance Imaging I and II
35(2008); http://dx.doi.org/10.1118/1.2962325View Description Hide Description
The applications of magnetic resonance imaging(MRI) in biomedicine are undergoing rapid evolution. Typically used to produce images that are viewed and subjectively rated by a radiologist,MRI is now being utilized as a scientific apparatus capable of making noninvasive measurements in living tissues. With care, a significant number of physical and biological measurements can be performed and related to individual pixels and groups of pixels in the MRimage. This presentation will address the challenges in obtaining quantitative data from MRI.
The presentation will review the principles of good practice in quantification, including quality assurance,MR data collection, and analysis. Limits on precision and accuracy are discussed and solutions proposed. Three major topics are considered. First, the signal collection process in MRI will be reviewed concentrating on geometrical relationships derived from MRimages and signal‐to‐noise considerations. Then, physical sources of quantitation errors in MRI will be considered; especially resonant frequency offsets, radio frequency (RF) attenuation, dielectric phenomena and eddy current effects. Third, common quantitative measurements using MRI will be explored. The principles underlying the measurement of each quantity are given along with their biological and medical significance and practical approaches for achieving their accurate measurement. Shortcomings of the measurement processes and a summary of potential clinical applications are also discussed. Pathological and developmental observations will be also compared with MRI‐derived quantities where appropriate.
This presentation is intended as an introduction to the field of measurement in MRI for anyone who desires to use the scope of modern measurement techniques to quantitatively determine the consequences of disease, its development or its reaction to therapy from MRimages. It will be of interest to medical physicists who are considering undertaking quantitative work with MRI, as well as those already in the field.
1. Appreciate the clinically important quantities that can be measured with MRI.
2. Be familiar with the methods and techniques used for quantitative MRI.
3. Have a basic understanding of the limits on precision and sources of error in quantitative MRI.
MO‐SAMS‐332‐02: Introduction to Magnetic Resonance Spectroscopy of Breast and Prostrate Cancer: Current Applications35(2008); http://dx.doi.org/10.1118/1.2962326View Description Hide Description
Magnetic resonance spectroscopy (MRS) and magnetic resonance spectroscopy imaging(MRSI) is increasing being utilized as adjuncts for differentiating benign from malignant lesions in the clinical setting. MRS has the ability to probe intracellular metabolites, such as, choline (Cho), Creatine (Cr), citrate (Ci) and N‐acetylaspartate (NAA). The observation of a high Choline signal appears to be the spectroscopic hallmark of cancer. This additional information can be very useful in cases of indeterminate findings in suspicious lesions, for example, in breast or prostrate cancer. Indeed, recent advances have moved the use MRS into the clinical realm for detection and classification of these tumors and more importantly, monitoring response to neoadjuvant chemotherapy treatment. This presentation will review the principles of MRS, including, pulse sequences, MRS data collection, data analysis, quantification, and quality assurance. Three major topics are considered. Introduction of relevant intracellular metabolites and their biological and medical significance in cancer, the principles underlying each quantity are given. Second, major pulse sequences used for MRS, e.g., PRESS or STEAM in breast and prostrate cancer. Finally, MRS data analysis and quantification of the results with pathological observations will be also compared with MRS‐derived quantities where appropriate.
This presentation is intended as an introduction to the field of MRS for anyone who desires to use the scope of modern MRS techniques, its application and use for monitoring therapy. It will be of interest to medical physicists who are considering undertaking quantitative MRS, as well as those already in the field.
1. Identify the clinically important quantities (e.g. metabolites) that can be measured with MRS.
2. Be familiar with the methods and techniques used for MRS acquisition.
3. Basic understanding of the application of MRS to breast and prostrate cancer.
CE‐Imaging: Breast Imaging II
35(2008); http://dx.doi.org/10.1118/1.2962418View Description Hide Description
The medical physicist provides a valuable service to mammography facilities by helping to ensure the production of high quality images at a low radiation dose. This presentation will describe the role of the medical physicist in mammography QA and equipment performance evaluation of film‐screen systems. Individual tests for both initial and annual equipment evaluations will be described. Special attention will be paid to potential pitfalls, common problems and ways to increase efficiency of the testing process.
1. Review medical physicist responsibilities in film‐screen mammography QA.
2. Learn about the specific requirements involved in testing for new equipment installations.
3. Review quality control procedures for annual equipment performance evaluations.
4. Learn about ways to streamline equipment performance evaluations.
35(2008); http://dx.doi.org/10.1118/1.2962419View Description Hide Description
Digital mammography is quickly becoming the technology of choice for breast imaging with several FDA‐approved systems already available and more on the way. Digital detectors in mammography have different characteristics compared to the traditional screen‐film systems and require by the FDA different Quality Control tests. This lecture is going to discuss the practical issues for the medical physicist who wants to learn the differences in these Quality Control tests and how they impact the mammography facility and ACR accreditation. The lecture will be broken into several parts. The first will review currently available FFDM equipment and their respective Quality Control tests. The second part will compare similar QC tests and discuss the key differences. The third part will review quality control for review workstations and laser printers designed for digital mammography.
1. To describe current quality control procedures for FFDM systems.
2. To describe current quality control procedures for review workstations in digital mammography.
3. To describe current quality control procedures for laser printers in digital mammography.
4. To review the impact of QC on ACR accreditation for FFDM systems.
CE‐Imaging: PET/CT and SPECT/CT: Applications and Quality Assurance
35(2008); http://dx.doi.org/10.1118/1.2962671View Description Hide Description
In the past few years, positron emission tomography/computed tomography (PET/CT) imaging has increasingly been used for the diagnosis, staging, and restaging of malignant diseases. The success of this emerging modality has primarily been due to its ability to combine the advantages of both PET and CTimaging while minimizing their separate weaknesses. One of the main advantages of PET/CT imaging is its ability to generate functional images depicting the biodistribution of radioactive compounds that are correlated with anatomical landmarks thereby increasing physicians' confidence in image interpretation and improving patient management.
The aim of this lecture is to provide an overview of the basic physics principles of PET/CT imaging as well as the advantages and drawbacks of using CT for attenuation correction of PETimages. In addition, the lecture will cover the latest in design specifics of commercially available PET/CT scanners from different manufacturers as well as review PET/CT quality control and assurance techniques.
1. To learn the basic physics principles of PET/CT imaging.
2. To understand the advantages and drawbacks of using CT for attenuation correction of PETimages.
3. Become familiar with design specifics of commercially available PET/CT scanners.
4. Learn quality control and assurance techniques for PET/CT imaging.
35(2008); http://dx.doi.org/10.1118/1.2962672View Description Hide Description
Hybrid SPECT/CT is rapidly becoming a mainstream imaging modality, with the recent commercial introduction of systems that incorporate state‐of‐the‐art multi‐slice, diagnostic CTscanners. The ability to acquire contemporaneous, electromechanically registered dual‐modality scans has created a new paradigm for SPECTimaging. The first generation, single‐slice hybrid scanner produced acceptable attenuation coefficient (mu) maps for SPECT attenuation correction, however the quality of its anatomical overlay CT for SPECT/CT fusion imaging was limited. The CT integrated into the latest generation of hybrid systems is a fully‐functional diagnostic scanner. In addition to generating high‐quality mu maps, these systems can produce diagnostic image quality CT scans with variable scan parameters (speed, collimation, pitch, mA, slice thickness and FOV), that are capable of greatly improving both the localization and specificity of abnormalities detected on the corresponding SPECT scan. In some cases, these systems are also capable of performing billable diagnostic CT scans with contrast enhancement.
The widest use of SPECT/CT is currently in oncology, with applications including: tumor localization, staging and response to treatment; presurgical mapping (e.g., parathyroid adenomas, sentinel lymph nodes); differentiation of skeletal metastases from other disease processes; functional image‐based radiation therapy treatment planning (e.g., lung perfusion); and quantitative SPECT/CT‐based internal radionuclide therapy dosimetry/treatment planning. Cardiac SPECT/CT is currently focused primarily on improved attenuation correction of SPECT myocardial perfusion images; although the newest, 16‐to‐64‐slice integrated scanners offer the potential for contemporaneous CTcardiacimaging (e.g., coronary angiography, calcium scoring). SPECT/CT is also being utilized for imaging bone and other non‐malignant diseases.
This lecture will review the underlying physics of SPECT/CT imaging, present several examples of the clinical application of SPECT/CT, and provide an overview of the currently available SPECT/CT scanner types and models.
1. To understand the underlying physical principles of SPECT/CT image acquisition, processing and reconstruction.
2. To understand current and future clinical applications of SPECT/CT imaging.
3. To become familiar with the various commercially‐available SPECT/CT product offerings.
CE‐Imaging: Physics and Technology of Computed Tomography IV
35(2008); http://dx.doi.org/10.1118/1.2962813View Description Hide Description
Facilities participating in the American College of Radiology Computed Tomography Accreditation Program require significant support from Medical Physicists. A number of presentations in prior years have covered the mechanics of preparing a submission to the program. Recently, changes and clarification were made to the program. Rather than covering the basics of scanning the phantom, this presentation will focus on these recent changes and some common pitfalls and how to avoid them. Issues around dosimetry measurements will be covered. Finally, areas where Medical Physicists can provide additional support to facilities will be briefly discussed.
1. To become aware of the new dose limits of the ACR CT Accreditation Program.
2. To gain an understanding of some of the common application pitfalls and how to avoid them.
3. To gain insight regarding the role of the Medical Physicist within a clinical CT program.
35(2008); http://dx.doi.org/10.1118/1.2962814View Description Hide Description
The American College of Radiology CT accreditation program was launched in 2002. It has approximately 3320 active units and is growing daily.
All sites that apply for CT accreditation receive a testing packet with the necessary paperwork and labels required for their testingmaterial submission. CT accreditation involves the submission of clinical and phantom images. Qualified radiologists and medical physicists review all submissions.
The medical physicist plays a vital role in the achievement of ACR accreditation. A team approach involving the supervising physician, lead technologist and medical physicist is necessary to ensure that all information is accurate and appropriate for ACR accreditation submission.
For sites with filming capability, the phantom testingimages are submitted on hard copy film. As more and more sites become film‐less, the need for electronic submission of phantom testingmaterial has increased. Sites that have no filming capability can call the ACR and receive permission and instructions for submitting the CT phantom images electronically. Electronic phantom submission is currently a pilot program as the ACR actively works to define the process.
1. Understand the basic materials and process of ACR CT accreditation.
2. Understand the importance of a “team approach” in achievement of ACR accreditation.
3. Understand the process of electronic submission of the CT phantom images.
35(2008); http://dx.doi.org/10.1118/1.2962815View Description Hide Description
Conebeam CT using C‐arm mounted large area flat panels (FPs) is becoming more commonly used in neuro‐ and body‐interventional suites. The ability to visualize vascular geometry in 3D along with soft tissueduring an intervention is providing information that may increase accuracy, shorten procedure time and may even change the course of treatment. However, acquisition of the projection data required for volume imaging requires dose to the patient, and understanding the trade‐offs between acquisition parameters, dose and image quality is critical to the appropriate adoption of this imaging technique.
Unlike conventional CT, the beam length in conebeam CT can cover the entire length of the object to be imaged or can be varied with the use of collimation, and the concept of CTDI is not, therefore, the metric of choice for measurement of dose. In addition, most C‐arm conebeam CT systems use a short‐scan (pi plus fan‐angle) acquisition, and the dose distribution within the object is not cylindrically symmetric. Finally, since FP design has been optimized for fluoroscopy, image quality when used for CT must be carefully evaluated.
This lecture will describe a dose metric that is appropriate for conebeam CT and allows direct comparison with the CTDIw of conventional CT. A perception study using the CATPHAN 600 phantom for a range of acquisition parameters will be described, and the relationships between kVp, image noise, dose and contrast perception will be discussed.
Research sponsored by Siemens Medical Solutions AG, AX Division, by NIH grant R01 EB003524 and by the Lucas Foundation.
1. Understand how differences in acquisition geometry between conebeam and conventional CT affect dose distribution and dose measurement.
2. Understand how contrast perception in conebeam CTimages depends on acquisition parameters.
35(2008); http://dx.doi.org/10.1118/1.2962816View Description Hide Description
Computed tomography(CT)dosimetry should be adapted to the fast developments in CT in order to keep pace with new CT technology. Recently, a cone beam CT scanner that challenges the existing Computed Tomography Dose Index(CTDI)dosimetry paradigm was introduced. The appropriateness of existing CT dose metrics for a cone beam CT scanner will be assessed and to new approaches for CTdosimetry will be suggested.
Dose measurements with a small Farmer type ionization chamber, and 100mm and 300mm long pencil ionization chambers can be performed free‐in‐ air to characterize the cone beam. According to the most common dose metric in CT, measurements can also performed in 150mm and 350mm long CT head and CT body dose phantoms with 100mm and 300mm long ionization chambers. Effects that cannot be measured with ionization chambers can be explored with Carlo calculations of the dose distribution in 150mm, 350mm and 700mm long CT head and CT body phantoms. To overcome inconsistencies in the definition of CTDI, doses are also expressed as CT_Dose100 (CT_Dose100=160/100 × CTDI100). CTDI300 is chosen as the standard of reference against which results were assessed.
Measurements free‐in‐air reveal good‐to‐excellent correspondence between CTDI300air and CT_Dose100air; CTDI100air substantially underestimates CTDI300air. Measurements in phantoms and Monte Carlo calculations reveal good correspondence between CTDI300w, CT_Dose100w and CTDI600w; CTDI100w substantially underestimates CTDI300w. Measurements at different positions within CT dose phantoms with an ionization chamber that is smaller than the cone beam are fundamentally different compared to readings of pencil chambers that are longer than the cone beam.
CT_Dose100air and CT_Dose100w are pragmatic metrics for characterizing the dose of the cone beam CT scanner; these quantities can be measured with the widely available 100mm pencil ionization chambers and 150mm long CT dose phantoms. CTDI300air and CTDI300w in a 350mm long CT dose phantom can serve as appropriate standards of reference for characterizing the dose of the cone beam CT scanner. Simple geometrical considerations, supported by Monte Carlo calculations, explain the fundamental differences of different CT dose metrics when measurements are performed at different position within CT dose phantoms.