Volume 35, Issue 6, June 2008
Index of content:
- Imaging: Continuing Education Course: Room 342
- CE‐Imaging: Radionuclide Imaging I
35(2008); http://dx.doi.org/10.1118/1.2962327View Description Hide Description
Because of resistance to chemotherapy and multiple sites of disease, internal emitters are being more frequently used in treating advanced cancer patients. This radiotherapy is predicated upon injection of beta‐ or alpha‐labeled antibodies and other agents that target tumor markers. Most clinical success has occurred in the case of B‐cell lymphoma and hepatic lesions. For associated treatment planning, estimate of radiationdose (D) to tumors and normal tissues requires application of the equality where S is a rectangular matrix and Ã is a set of total decays for each source tissue. While S may be determined via Monte Carlo(MC) methods, Ã requires that the observer integrate time‐activity curves for each source. Quantitation of activity at depth in patients has been a continuing problem in nuclear medicine. Multiple methods have been developed ranging from direct counting (surface lesions), through geometric mean estimates (GM) to hybrid techniques (SPECT/CT) involving nuclear and CT scans. In the last strategy, attenuation may be taken directly from the CT data set. Quantitative SPECT (QSPECT) studies typically involve such hybrid imaging techniques and correct for attenuation, scatter, collimator geometry and partial volume effects. Accuracy of these methods, as measured by phantom studies, varies from +/−; 30% (GM) to as little as +/− 5% for QSPECT. While PET/CT may also be considered, the limited number of positron emitters causes this application to be more problematic. Time considerations make extensive use of QSPECT difficult. Standard clinical procedure follows Koral et al (Cancer Biother Radiopharm. 2000; 15; 347–355) in combining GM at the requisite multiple time points with an overlap of QSPECT at one time point. The latter study is then used to normalize the geometric mean values and improve quantitation of activity. Finally, we must note that two types of dose estimate are being done: phantom (Type I) and patient‐specific (Type II). In the former case, a standard geometry is applied assuming; e.g., the OLINDA program. Here, the patient or volunteer activity integral must be corrected for relative mass differences between phantom and patient. With Type II, the patient's own organ geometry is used to generate an S matrix. This may be done directly with MC techniques or a phantom value may be corrected by the target organ mass differences between the phantom and patient. If these corrections are not made, errors in S may be on the order of several‐fold. Uncertainty in resultant D values is estimated by combining errors in S and Ã.
1. Know how to estimate internal emitter doses via .
2. Understand various methods to quantify activity at depth in patients.
3. Realize that both phantom and patient dose estimates are needed.
4. Understand the size of errors involved in dose estimation.
- CE‐Imaging: Imaging: Radiation Safety and Risk Management I
MO‐B‐342‐01: Magnitude of Medical Radiation Exposures to US Population with Focus On CT and Nuclear Medicine Doses35(2008); http://dx.doi.org/10.1118/1.2962334View Description Hide Description
This presentation will examine the current trends in medical x‐ray imaging procedures in the United States. It will also examine the magnitude of radiation doses for various x‐ray imaging procedures. Special emphasis will be given to CT and nuclear medicine procedures.
The results are based on the work done within the framework of National Council of Radiation of Protection Scientific Committee 6.2 formed 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. 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 radiation doses associated with each procedure.
According to the preliminary results, the medicalradiation exposure to US population has increased by nearly 5.5 times compared to the previous NCRP publication (NCRP 93). The largest contributor to the collective dose to US population is seen with CT and Nuclear Medicine procedures. It is found that the CT procedures accounts for 14% of all medical x‐ray imaging procedures but contribute to nearly 49% of collective dose to US population. Similarly, the nuclear medicine procedure accounts to only 4% of all procedures but contribute to nearly 26% of collective dose to US population.
1. To familiarize with the types and distribution of medical imaging procedures in US.
2. To learn the magnitude of medicalradiation exposure to US population.
3. To examine the magnitude and distribution of procedures and doses from CT.
- CE‐Imaging: Radionuclide Imaging II
35(2008); http://dx.doi.org/10.1118/1.2962420View Description Hide Description
Routine maintenance, calibration, and quality control of gamma camera and SPECTimaging systems is crucial for providing the nuclear physician or radiologistimages of high quality without artifact. This lecture will provide an overview of the gamma camera and SPECTcalibrations, performance measurements, and quality assurance tests, whether they are for routine quality control or annual physics surveys as defined by the ACR accreditation program. A discussion of common artifacts and how to avoid and correct them will be included.
Gamma camera and SPECT performance measurements are well defined in documents published by MITA/NEMA and in AAPM Task Group reports. Unfortunately, many of the specified tests cannot be easily done on installed systems in the field. Modifications become necessary, and as a result performance measurements and quality assurancetesting of gamma camera and SPECT systems have been quite variable. Not included in the published documents are calibration procedures that are vendor specific. Improper calibrations, particularly uniformity calibration, also lead to unwanted artifacts. It is the burden of the physicist to know which performance tests are critical in the field and to also become familiar with specific calibration procedures of our gamma camera and SPECT systems.
1. Learn the basic gamma camera and SPECT performance measurements and quality assurance test procedures.
2. Become familiar with calibration procedures of current systems.
3. Become familiar with the test procedures and the frequency of testing prescribed by the ACR accreditation programs.
4. Be able to identify common gamma camera and SPECTimage artifacts and how to correct them.
- CE‐Imaging: Imaging: Radiation Safety and Risk Management II
35(2008); http://dx.doi.org/10.1118/1.2962426View Description Hide Description
This presentation will discuss the dosimetric factors associated with PET/CT and SPECT/CT including those associated with the administration of radiopharmaceuticals for both PET and SPECT and the specific factors associated application of CT in these hybrid modalities. The dosimetry of the application of these modalities to pediatrics will also be discussed. For SPECT, the dosimetry of the administration of radiopharmaceuticals typically used in SPECT as well as potential methods for maintaining these doses at reasonably low levels. In particular, myocardial perfusion imaging will be discussed. Also the use of new reconstruction techniques and how they may be used to lower the administered activity for some SPECT applications will be discussed. For PET, the dosimetry associated with the use of fluoro‐deoxy‐glucose (FDG) will be discussed including different technical approaches that may lead to lower administered activity. Lastly, the application of CT to both SPECT and PET will be discussed including the requirements for CT‐based attenuation correlation, anatomical correlation and diagnostic CT. Potential methods to reduce CT dose in these protocols will be discussed.
1. Discuss 2 potential ways to reduce the administered activity in SPECT.
2. Describe 2 ways that the acquisition of PET can be modified to make it more efficient.
3. List 3 approaches that can be used to reduce the dose of the CT used in conjunction with PET and SPECT.
- CE‐Imaging: The Physics and Technology of Magnetic Resonance Imaging IV
35(2008); http://dx.doi.org/10.1118/1.2962673View Description Hide Description
Drugs, known as “Magnetic Resonance (MR) Contrast Agents (CA)” are firmly established in current clinical practice. According to recent data, MR CAs are administered in about 25–30% of all MR Imaging(MRI) procedures; it is estimated that in 2005 about 20 million procedures involving injected CAs were performed worldwide. In standard applications, they are administered intravenously with the intent to modify the Nuclear Magnetic Resonance (NMR)characteristics of tissues. Since the extent of contrast agent impact varies with tissue type, the differential effect of drug action on imaged lesions modifies their appearance on MR images. This phenomenon is used to aid the clinical diagnosis.
Physical principles governing the behavior of CAs are discussed first, with emphasis on mechanisms that play a major role in MRI applications. CA's main role is to modify the NMR relaxation properties (longitudinal relaxation time T1, transverse relaxation time T2, or both) of its molecular environment. Since the effect is proportional to CA's concentration in the tissue, the biodistribution of CA has a major impact on the overall efficacy of the drug. Thus, in addition to NMR relaxation processes, fundamentals of compartmental analysis are discussed. The segment is concluded with taxonomy of CAs currently available for clinical use.
The second part of the presentation describes clinical applications of MR CAs. Currently, routine applications explore non‐organ targeted relaxation enhancement mechanisms of action. In this method, a bolus of CA is injected intravenously and data collection for MRI begins a few minutes later, after tissue uptake mechanisms have established stationary conditions throughout the patient's body. Abnormalities within organs accumulate higher concentrations of CA, which shortens their T1 relaxation time and makes them appear brighter (relative to their background) on T1‐weighted MR images. However, two major off‐label areas of use have emerged already: contrast‐enhanced MR Angiography (MRA) examinations and Dynamic Contrast Enhancement (DCE) studies of tissue perfusion. Strengths and weaknesses of these techniques are reviewed. The segment ends up with a discussion of tissue‐specific CAs, such as superparamagnetic iron oxides (SPIO) used in imaging of the liver.
The last part of the lecture focuses on the safety issues associated with the use of MR CAs. Despite rigorous pre‐market evaluations (MR CAs are considered drugs and are subject to FDA regulations) some side effects emerge only after the drug has been on the market for considerable time, when the large volume of available clinical records reveals patterns that remain hidden within smaller data pools. The recent alarm caused by emergence of the Nephrogenic Systemic Ribrosis (NSF) syndrome as a serious consequence of using Gadolinium‐based CA during MR studies in patients with acute or chronic kidney disease is used to describe and analyze safety issues related to the use of MR CAs.
1. Understand the physical mechanisms governing the action of contrast agents used in MR Imaging.
2. Become acquainted with the taxonomy of contrast agents used in current clinical practice.
3. Learn about safety issues related to the use of contrast agents in MRI practice.
- CE‐Imaging: Imaging: Radiation Safety and Risk Management III
35(2008); http://dx.doi.org/10.1118/1.2962681View Description Hide Description
CT coronary angiography (CTCA) has become a popular diagnostic test for patients with known or suspected coronary artery disease. CTCA generates images of sub‐millimeter spatial resolution and has been validated in multicenter clinical trials to have high predictive value to exclude coronary disease.
CTCA is now typically performed on a 64‐or‐greater slice multidetector‐row scanner in helical mode with low pitch. The resulting effective dose is on the order of 20 mSv, with breast and lung doses roughly 70 mGy. My colleagues and I have estimated potential cancer risks attributable to CTCA, using a combination of Monte Carlo methods to estimate organ doses of various protocols, and radioepidemiological modeling using the approach of the National Academies' Biological Effects of Ionizing Radiation (BEIR) VII report.
In this lecture, I will address the clinical utilization of CTCA, methodology for estimating attributable cancer risks, cancer risk from CTCA, and the effects of patient age, gender, and scan protocol on risk.
1. Understand the information provided by CTCA, in comparison to other cardiac imaging modalities.
2. Know typical organ and effective doses from CTCA.
3. Learn how cancer risk attributable to CTCA depends on age and gender.
4. Understand approaches to lower radiation dose and cancer risk from CTCA.
- CE‐Imaging: The Physics and Technology of Magnetic Resonance Imaging V
35(2008); http://dx.doi.org/10.1118/1.2962817View Description Hide Description
In 2006, the ACR council approved a resolution requiring the current ACR MRI Accreditation Program to be redesigned into a modular program. The current program is limited to only whole‐body and cardiac accreditation. The new modular program will offer six clinical modules and is designed to allow a facility to have an accreditation that is more appropriately matched to the individual practice and the patient population being served. The six modules are: body, head, MR angiography (MRA), spine, musculoskeletal and cardiac. A breast MR accreditation program is currently under development; however, will not be one of these MR modules. Instead, it will be part of the Breast Imaging Accreditation Program. Also, an accreditation program specifically designed for special‐purpose orthopedic systems is under development.
This continuing education course will review the current status and requirements of the ACR Whole Body MRI Accreditation Program, anticipated changes related to the proposed modular program and anticipated changes in the MRIQuality Control Manual as related to the Annual Medical Physicist Performance Survey.
1. Review the role of the Medical Physicist in the current Whole Body Accreditation Program with emphasis on the requirements of the annual performance survey.
2. Discuss the status of the proposed ACR modular accreditation program as well as the new initiatives into cardiac and orthopedic accreditation and the anticipated impact that these changes will have on the role of the medical physicist.
3. Discuss special accreditation considerations related to 3T systems and for systems with parallel imaging capability.
- CE‐Imaging: Imaging: Radiation Safety and Risk Management IV
35(2008); http://dx.doi.org/10.1118/1.2962824View Description Hide Description
Image‐guidedradiation therapy(IGRT) makes it possible to locate the treatment target before each radiationdose is delivered while the patient is in the treatment position. It not only minimizes the volume of normal tissue exposed to radiation during treatment but also ensures adequate dose to the treatment target. With the advance of technology, IGRT has emerged as the new paradigm in radiotherapy. The increased clinical availability of new emerging imaging procedures, such as cone beam CT, has resulted in a dramatic growth in its usage and therefore, IGRT procedures may also entail new risk to radiosensitive organs. Unlike diagnostic imaging in radiology, image‐guided procedures are performed much more frequently or daily. Knowledge of radiationdose to patients and accurate dosimetry of radiationdose to organs from each imaging procedure is becoming increasingly important for clinicians as information to consider in making informed decisions regarding the increased dose to radiosensitive organs. This lecture will provide an overview of the commonly used image‐guided rocedures and discuss recent advances in the accurate dosimetry for these imaging procedures, especially for emerging cone beam CT scans. The x‐ray imaging procedures in radiotherapy include megavoltage electronic portal imaging (MV EPI), kilovoltage digital radiography (kV DR), megavoltage cone‐beam CT (MV‐CBCT) and kilovoltage cone‐beam CT (kV‐CBCT).
1. Understand the commonly used image‐guided procedures in radiation therapy and differences between diagnostic x‐ray imaging and image‐guidanceimaging.
2. Obtain a prospective view about radiationdoses to organs from each image‐guided procedure, especially cone beam CT.
3. Learn the large variations between dose to bone (or bone marrow) and dose to soft tissues for x‐rays at kilovoltage energy range.