Slide 1:Presented by: Meylen Reyes


Objectives :Objectives Explain the acquisition protocol considerations for combined PET/CT imaging Discuss the standard FDG PET/CT imaging protocol Describe its patient preparation, patient positioning and CT and PET acquisitions Discuss the optimization standard of 18F-FDG PET/CT imaging protocols Explain respiration artifacts Discuss CT contrast agents Discuss metal implants Explain combine scanning and joint report


Objectives :Objectives Describe special FDG PET/CT imaging protocols Discuss software approach to merging molecular with anatomic information Explain the different image acquisition algorithms Discuss validation and visualization techniques Describe the clinical applications for software registration


Standard FGD PET/CT Imaging Protocol :Standard FGD PET/CT Imaging Protocol Detects primary and metastatic disease Whole body with a single injection of a radiotracer (2-18F-FDG) Based on standard whole-body PET acquisition protocols


Patient Preparation :Patient Preparation Questioned for allergies to iodine-based CT contrast Drink up to 1,500 mL of oral contrast during the 18F-FDG uptake phase


Overview Scan :Overview Scan PET/CT examinations start with acquisition of a topogram Acquired during continuous table motion, with the x-ray tube detector Used to define the axial examination range of the PET/CT study


CT & PET Acquisition :CT & PET Acquisition CT Patient is moved automatically into the CT FOV Breath-hold command is given to match the anatomy more closely to the physiology PET When done with CT, patient is moved into the FOV of PET Combined scanning is completed in 30 min.


Optimization of standard 18F-FDG PET/CT Imaging Protocols :Optimization of standard 18F-FDG PET/CT Imaging Protocols Requires addressing the often conflicting goals for PET and CT PET/CT is acquired using oral or IV contrast agents to maximize the diagnostic information on anatomy and tumor vascularization CT is used as a fast transmission source for attenuation correction, anatomic labeling, or referencing of the PET results


General aspects of 18F-FDG PET/CT :General aspects of 18F-FDG PET/CT By using Ct as attenuation correction instead of 68Ge-rod sources, whole body scan times are reduced as much as a third to 30 min. or less Most patients tolerate being scanned with arms raised and supported above the head By raising the arms and keeping them outside the CT FOV, scatter artifacts are reduced All patients should be supported wit ha proper knee rest for the duration of the scan


Truncation Artifacts :Truncation Artifacts Patient positioning supported by positioning aids is important for reducing truncation artifacts Spiral CT offers a transverse FOV of 50 cm, which is 10cm less than the transverse PET FOV Truncation artifacts are seen on very large patients or if imaged with arms down


Respiration Artifacts :Respiration Artifacts Potential artifacts are the mismatches of breathing patterns Severe when standard breath-hold technique from clinical CT to PET/CT without adaptation Patient is asked to hold their breath in normal expiration only for the time that the CT takes to cover the lower lung and liver


Metal Implants :Metal Implants Chemotherapy ports, metal braces in the spinal region, artificial joints, or dental filling In PET they cause little or no artifact Can be severe at CT energies because of higher proton absorption from high-Z materials Chemotherapy ports have high density properties and low attenuation properties of the surrounding tissue This may be misleading in the diagnosis when true lesions are present in the vicinity of these ports


Combine Scanning and Joint Report :Combine Scanning and Joint Report Current package software allow to correlated review of PET and CT data either side by side or infused mode The primary concept of PET/CT is the immediate transformation of the functional information from PET into the spatial coordinate system of CT


Special FDG PET/CT Imaging Protocols :Special FDG PET/CT Imaging Protocols PET/CT studies involving the head and neck suffer form local misalignment in the region of the neck because of the relaxation of its muscles A vacuum pillow is used to support the neck and head for the duration of the examination Imaging parameters can be adjusted to torso and neck scanning Patient can be positioned and supported more efficiently for each scan Patient can get off the table between the two partial examinations if needed


Software Approach to Merging Molecular with Anatomic Information :Software Approach to Merging Molecular with Anatomic Information Software image registration is a powerful and versatile tool that allows the fusion of molecular and anatomic information Can be applied to compare anatomic information with function, localize organs and lesions New applications in cardiology could allow the combination of CT angiography with perfusion and image obtained from PET, SPECT, or MRI


Image Registration Algorithms :Image Registration Algorithms Feature-based algorithms Seek to align corresponding anatomic landmarks and organ surfaces Extract relevant features (points, contours, surfaces) Spatial alignment of these features Volume-based algorithms Has been introduced to maximize measures of similarity between images Do not depend on image segmentation but exploit the statistical voxel dependencies of the raw image pairs to find the appropriate alignment


Image Registration Algorithms :Image Registration Algorithms Volume-based algorithms Possible modifications can improve their reliability and speed Matrix size can be increased as the images become closely aligned Nonlinear Registration Images of thoracic and abdominal require it to compensate for changes in body configuration Breathing, movement of internal organs Techniques may be automated, because the number of adjustable image parameters can be large


Visualization Techniques :Visualization Techniques Fusion Display Anatomic images such as CT or MRI are displayed using gray-scale tables Functional information derived from PET and SPECT can be depicted with high contrast using color Alternative Display Options An effective multimodality display tool is a pair of synchronized cursors displayed simultaneously in both images No information is lost and features don’t interfere with each other


Clinical Applications for Software Registration :Clinical Applications for Software Registration Neurology Pet or SPECT has been used PET/MRI brain images could be used for partial volume correction of PET Enhancing quantitative accuracy for measurements of cerebral blood flow, glucose metabolism and neuroreceptor binding Oncology First application of software registration were reported in brain oncology Treatment plans that incorporate SPECT or PET have been performed for cancers of the brain, lung, head and neck


Clinical Applications for Software Registration :Clinical Applications for Software Registration Cardiology Multimodality fusion is currently not used in clinical cardiac imaging Perfusion defects defined by SPECT or PET could be matched with the location of stenosis obtained by coronary CT angiography


Future :Future Merging anatomic and molecular information is useful clinically, as recently demonstrated by hybrid PET/CT Retrospective software-based methods must match that simplicity by full automation and transparent access to data PET/CT images could be coregistered to MRI with high accuracy in a nonlinear fashion Both modalities contain correlating anatomic details


Limitations :Limitations The most difficult application for software registration is multimodality imaging of the head and neck The abdominal and thoracic regions also can be deformed Essentials for the routine use of software registration Connectivity and compatibility Cooperation between departments Flexibility in patient scheduling


Software or Hardware? :Software or Hardware? Hybrid SPECT/CT and PET/CT scanners have become highly used in diagnosing oncology applications MRI is superior to CT in oncologic brain imaging Software registration may prove practical for clinical radiotherapy applications


Summary :Summary Explain the acquisition protocol considerations for combined PET/CT imaging Discuss the standard FDG PET/CT imaging protocol Describe its patient preparation, patient positioning and CT and PET acquisitions Discuss the optimization standard of 18F-FDG PET/CT imaging protocols Explain respiration artifacts Discuss CT contrast agents Discuss metal implants Explain combine scanning and joint report


Summary :Summary Describe special FDG PET/CT imaging protocols Discuss software approach to merging molecular with anatomic information Explain the different image acquisition algorithms Discuss validation and visualization techniques Describe the clinical applications for software registration


References :References Czernin, Johannes, MD. PET/CT: Imaging Function and Structure. Volume 45, supplement 1, January 2004.