Volume 33, Issue 6, June 2006
Index of content:
- Imaging Continuing Education Course: Room 330 D
- CE: PET Physics and Technology ‐ I
33(2006); http://dx.doi.org/10.1118/1.2241388View Description Hide Description
Over the past ten years, the use of clinical PET, particularly in the field of oncology, has increased dramatically. More recently, the introduction of hybrid PET/CT scanners has led to an enhanced ability to provide anatomical correlation to the functional findings on the PET scan. And lastly, the growing field of molecular imaging has led to the development of a variety of dedicated PET systems for small animal imaging. In the clinical arena, the goal is to develop scanners with higher sensitivity and count rate capability to be able to acquire whole body scans more efficiently. Efficiency is essential with respect to small animal imaging as well, but it must be accomplished with very high spatial resolution. This presentation will review the basics of PETimaging with a look towards the advances being made to address the needs of these two very different imaging tasks. The use of 2D versus 3D will be discussed as well as the effect using different crystal materials. Other advances being actively pursued such as the use of time‐of‐flight PET will also be discussed.
After attending this presentation, the attendee will be able to list 2 advantages and 2 disadvantages of 3D PET compared to 2D PET for clinical, whole body imaging, name 3 different materials used in state‐of‐the‐art PETscanners and list 2 advantages of each, and discuss two potential advantages for time‐of‐flight PET.
- CE: Radiography Physics and Technology ‐ I
MO‐B‐330D‐01: Design and Performance Characteristics of Computed Radiographic Acquisition Technologies33(2006); http://dx.doi.org/10.1118/1.2241395View Description Hide Description
Digital Radiography (DR) using Storage Phosphors, also known as Computed Radiography (or CR), has been commercially available for a quarter of a century. Each new generation of scanners and screens has brought improvements in image quality, throughput, physical size and cost. With these improvements has come a high level of clinical acceptance, with a corresponding displacement of screen/film systems as the standard for projection radiography acquisition.
Scanner improvements include better, more reliable light sources, more efficient light collection systems, higher quality photodetectors, and better electronics. The latest CRscanner advances have done away with traditional flying‐spot (point‐at‐a‐time) scanning in favor of line‐at‐a‐time scanning, bringing significant throughput, image quality, and size advantages. At the same time, advances in the design and manufacture of powder‐based, particle‐in‐a‐binder CR screens, or image plates, have enabled improved inherent signal and noiseproperties (x‐ray absorption, Modulation Transfer Function, Noise Power Spectra, Detective Quantum Efficiency, etc.), and a better matching of screen absorption and emission spectra to the scannercharacteristics. Screens with transparent substrates have produced improved image quality due to the ability to extract latent image signal from both sides of the screen. The latest storage‐phosphor screen materials can be grown in needle form, similar to the scintillators used in indirect flat‐panel detectors, resulting in dramatically improved image sharpness and higher x‐ray absorption due to the absence of binding material.
This presentation will review the form, function and performance of CR systems, with an eye towards more recent developments. The current state of the art in CR will be placed into the larger context of newer DR acquisition systems (e.g., active‐matrix flat panels), looking at the advantages and disadvantages of each. Advances made in CR technologies in recent years portend continued expansion of CR‐based medical imaging.
1. Describe the form and function of today's computed radiography(CR) systems.
2. Identify the main factors that influence the image quality of CR systems.
3. Compare modern CR systems to other acquisition technologies.
4. Describe the latest and future developments in CR.
Conflict of Interest Statement
The author is employed by Agfa Corporation.
- CE: PET Physics and Technology ‐ II
33(2006); http://dx.doi.org/10.1118/1.2241480View Description Hide Description
In order for an annihilation event to be accurately detected in a PETscanner, it is necessary for both annihilation photons to pass through the patient without interaction and be detected by two detectors in the scanner. The probability of this occurrence is less than that for a single photon, resulting in significant attenuation effects in a PET scan. In the past, a positron source, such as Ge‐68, was used as a transmission source to provide a transmission map to be used for attenuation correction. The recent integration of PETscanners with state‐of‐the‐art multi‐slice CTscanners has provided the capability for using the CT scan as a high‐quality attenuation map to accomplish the task of attenuation correction. This has resulted in an improvement in the quality of the correction and thus an improvement in overall PETimage quality. However this implementation has not been accomplished without additional problems being identified. Specifically beam hardening can cause errors in the attenuation correction and accurate corrections are difficult in regions where there is physiological motion such as the heart and lungs due to difficulties in accurately registered the CT and PET scans in these areas. Close attenuation must be paid to these effects.
Integration of the CTscanner with the PETscanner has provided a significant advance in clinical diagnosis and treatment planning because of the ability to accurately register and display high quality images of anatomy from CT and images of organ function from PET. This makes it possible not only to differentiate malignant from benign lesions but to also precisely localize malignant lesions and differentiate between abnormal uptake and normal physiological uptake of radiopharmaceuticals.
- CE: Radiography Physics and Technology ‐ II
33(2006); http://dx.doi.org/10.1118/1.2241487View Description Hide Description
Flat‐panel detectors are becoming more commonplace throughout the world for numerous applications ranging from mammography to megavoltage imaging and from static projection radiography to real‐time fluoroscopy and cone beam CT. A detailed understanding of their advantages and limitations is essential to ensure their efficient integration into the clinical environment. This presentation will review their place in the current DR detector landscape and the unique features that provide them with their improved image quality performance when compared to other approaches. The differences and similarities between the various flat‐panel designs will also be discussed with a view to highlighting their inherent image quality capabilities as well as some practical limitations to their performance. The process of gain/offset corrections will be reviewed and the issue of bad pixels, defective lines and image artifacts commented on. The implications of certain gain calibration procedures will be reviewed in terms of the possibility of image artifact creation, in particular in terms of other system components such as anti‐scatter grids and AEC circuitry. The impact of non‐linear behavior and pixel saturation will also be reviewed. In conclusion the development of advanced imaging applications such as dual energy, tomosynthesis and cone‐beam CT will be reviewed.
Conflict of Interest: John Yorkston is an employee of Eastman Kodak Company which sells DR systems based on CsI(Tl) type Flat‐Panel detectors.
1. Review the range of DR and flat‐panel detectors currently available and their design and performance differences.
2. Review the process of gain/offset calibration and its benefits and limitations.
3. Review the impact of pixel and line defects, correlated line noise, pixel saturation and other characteristics behaviors of flat‐panel detectors.
4. Review the prospect of advanced applications utilizing flat‐panel technology.
- CE: PET Physics and Technology ‐ III
33(2006); http://dx.doi.org/10.1118/1.2241664View Description Hide Description
Quality assurance of PETscanners must be performed on a regular basis to maintain and confirm proper scanner performance. These procedures should track system stability and be sensitive to changes in scanner operation. The quality control and calibration of a PETscanner includes detector and electronic characterizations such as adjustment of PMT gain, definition of crystal and energy maps and coincidence timing calibration. These characterizations are applied to the PET data during acquisition. A PETquality control regimen includes system corrections such as normalization, calibration and, in the case of non‐PET/CT systems, blank scans. The calibration correction is used to convert the reconstructed image pixel values into activity concentration and it may be used to compensate for the axial sensitivity variation of the scanner. These characterizations are applied to the PET data after acquisition.
The NEMA PET NU2‐2001 standard should be followed for acceptance testing. This standard uses a polyethylene phantom of 700mm axial length with a line source to measure scatter fraction, count losses and randoms. The measurement of sensitivity is conducted with a line source surrounded by known absorbers, and the sensitivity with no absorbers can be found by extrapolation. The intent of the image quality measurement is to mimic a whole body scan using a torso phantom containing hot and cold spheres of various diameters (representing lesions) in a warm background.
This presentation will focus on the calibrations and corrections required to maintain proper system performance. The presentation will also describe the rationale and methodology of the NEMA NU2‐2001 performance standards.
1. Describe the calibrations required to properly detect the location of a coincident event.
2. Describe the post acquisition corrections required to minimize image artifacts.
3. Describe NEMA NU2‐2001 PET performance standards.
- CE: Radiography Physics and Technology ‐ III
33(2006); http://dx.doi.org/10.1118/1.2241671View Description Hide Description
In digital radiography, the transmitted x‐ray beam recorded by a detector is first recorded as raw data related to the energy deposited in the sensitive region of each pixel. Raw data is then transformed to a ‘For Processing’ image by correcting for gain non‐uniformity and bad pixels. Finally, the ‘For Processing’ image is transformed to a ‘For Presentation’ image that is intended for viewing.
The processes used in the presentation transformation have become an ssential element of image quality. These processes include exposure recognition, grayscale rendition, edge restoration, noise reduction, and broad area equalization. The numeric methods used to implement these processes will be reviewed and related to current commercial image processingsolutions.
1. Understand how image processing is integrated. into a sequence of steps used in generating a radiograph.
2. Conceptually understand the component processing steps and their effect on image quality.
3. Learn how certain commercial systems implement processing.
4. Understand how processing can be adjusted by a medical physicist to achieve consistent presentation characteristics.
- CE: PET Physics and Technology ‐ IV
33(2006); http://dx.doi.org/10.1118/1.2241822View Description Hide Description
PET/CT imaging is a relatively new imaging modality that has become standard‐of‐care for the diagnosis and staging of many medical conditions. This has led to the widespread construction of new PET/CT installations. The design of such facilities, involving aspects of both nuclear medicine and radiology practice, presents some novel problems to the medical physicist. The recently issued report of AAPM Task Group 108, “PET and PET/CT Shielding Requirements,” addresses these difficulties and provides the designer with basic information needed for this work. The information from the report as well as the workflow in PET/CT facilities, the nature of the studies that are performed, the way in which to estimate patient workloads, and the computational approaches to radiation shielding design for high‐energy photon emitters will be discussed. Specific examples for the design of PET/CT shielding will be given.
1. To discuss the recently released report of AAPM Task Group 108 on PET and PET/CT Shielding Requirements and provide some specific examples of the methods described in that report.
2. To provide an overall understanding of the workflow, exam procedures, patient workloads, and radiation safety practices at PET and PET/CT imaging facilities.
3. To review the approaches and necessary data for calculating shielding requirements for PET isotopes.
- CE: Radiography Physics and Technology ‐ IV
33(2006); http://dx.doi.org/10.1118/1.2241830View Description Hide Description
The use of digital radiography is becoming the normal form of image capture replacing film. With film there are numerous Quality Assurance (QA) procedures that have been developed that cover the film processor, retake analysis, patient dose and overall system image quality. The QA procedures for digital systems are just now being developed. Since the digital detector technologies vary and with variations in image processing methods it may seem difficult to develop standardized QA procedures. Yet the endpoints of optimized image quality and minimized patient dose need to be obtained. Therefore the Physicist needs to use the knowledge of the detector characteristics and processing methods as tools to maintain QA on digital systems. These procedures need to be rigorous enough to provide QA, yet they must be flexible enough to work for different detectors, processing methods and system applications. This lecture will provide an overview of the testing procedures for digital radiographic systems and suggest procedures that can be used to provide QA in digital radiography.
1. Review detectortesting procedures used to assess digital systems.
2. Review QA procedures used in radiography and relate these to digital technologies.
3. Suggest QA procedures that can be used to evaluate digital systems.