COINCIDENCE IMAGINGWITH 18F-FDG :COINCIDENCE IMAGINGWITH 18F-FDG


Clinical Coincidence Systems :Clinical Coincidence Systems PET Scanner Molecular Coincidence Detection Gamma Camera (MCD)


PET Scanners :PET Scanners Technically well developed Tomographic Quantitative Complex to operate Expensive Single purpose


MCD Gamma Cameras :MCD Gamma Cameras New technology Simple to operate Relatively inexpensive Tomographic Multi-purpose Not yet quantitative


The Tools of the Trade :The Tools of the Trade Positron radioemitters Coincidence detection Radiolabeled sugars Powerful computers


Why Positrons? :Why Positrons? What is a positron? Positrons are positively charged electrons emitted during nuclear decay Annihilated quickly by negative electrons (negatrons)


PET Imaging :PET Imaging e+ e- 511 511 ANNIHILATION


Coincidence Detection :Coincidence Detection We only want to find events that arise from annihilation of positrons. Since these events are 180 degrees apart, we need two opposing detectors looking at the source. Using computers to time the arrival of photons at the source, we can determine which are coincident events.


The Power of Coincidence :The Power of Coincidence Scatter is markedly reduced Contrast and resolution are improved More counts for the same dose (better statistics) Potentially quantitative


Total Coincidence Count :Total Coincidence Count Total = Trues + Randoms + Scatter Random and scatter scatter account for ~ 25% in PET scanners, and ~ 30-50% in hybrid gamma cameras. Adds a flat background to the reconstructed images resulting in less contrast.


True Count :True Count Coincident detection of 511 KeV photons emitted from positron-electron annihilations that occurs within the sensitive volume of two opposing detectors. Trues count rate is proportional to the activity present within the sensitive volume 1 2


Random Count :1 2 Random Count Randoms = (Det 1 Singles) * (Det 2 Singles) * (Coincidence Timing Window) Coincident detection of un-correlated 511 KeV photons from positron-electron annihilations, leading to erroneous recording of projection ray. * *


Scatter Count :Scatter Count Coincident detection of 511 keV photons from a positron-electron annihilation, but one has scattered leading to erroneous recording of projection ray. * *


CORRECT PEAKING :CORRECT PEAKING


ATTENUATION CORRECTION :ATTENUATION CORRECTION The 137Cs attenuation correction source and 18F emission source energy peaks should be checked prior to each study with patient on the table The 137Cs sources must be removed prior to acquiring a study in normal mode. Otherwise, these sources will produce 100 cts/sec in normal imaging mode


ATTENUATION CORRECTION :ATTENUATION CORRECTION Attenuation correction creates a tissue density map to compensate for non-uniform densities in patient It compensates for varying body thickness, which will cause decreased activity in the midline of the patient Without transmission imaging, the FDG uptake in the lungs is artifactually high


FDG Attenuation Correction :FDG Attenuation Correction Important step to quantification Improves cardiac studies Improves visualization of deep structures Mediastinum Abdomen


Photon Attenuation Single Photon vs. Coincidence :Photon Attenuation Single Photon vs. Coincidence Attenuation higher—Coincidence path length is longer Coincidence Collimated Detector 1 Detector 2


Factors Affecting Attenuation Corrected Image Quality :Factors Affecting Attenuation Corrected Image Quality Large Patients Attenuation of deep structures Mediastinum Liver Abdomen Reconstruction Method Iterative vs. Filtered Back Projection Scatter and Random Corrections


Attenuation Correction(Reconstruction Methods) :Attenuation Correction(Reconstruction Methods) Filtered Back Projection Iterative


Transmission Acquisition :Transmission Acquisition Transmission Acquisition TX source translates Collimated fan beam Slit 13 cm by 58 cm Scanning window synchronized with source 360° continuous rotation Table movement


Attenuation Correction :Attenuation Correction Separate attenuation map created One rotation around patient (4-6 minutes) for each bed position Data sampling every 3.9 degrees Iterative reconstruction Reconstruct with or without AC using the same dataset


Slide 28:Transmission Projection Images Loyola University Medical Center Images adjusted for photography Reconstructed Attenuation Maps


Slide 29:Attenuation Correction Loyola University Medical Center No Attenuation Correction


Slide 30:Attenuation Correction No Attenuation Correction Loyola University Medical Center


Slide 31:Attenuation Correction No Attenuation Correction Loyola University Medical Center


Attenuation Correction/ No correction :Attenuation Correction/ No correction


Slide 33:Corrected Non corrected Loyola University Medical Center


Artifacts :Artifacts In 3/44 cases, artifacts such as streaking were seen on corrected scans In 20/44, cases artifacts were seen on the uncorrected scans that were not seen on corrected studies In 3/44 cases, artifacts were seen on both corrected and uncorrected data. When artifacts were seen on corrected studies, they were also seen on uncorrected studies.


Lesion Identification :Lesion Identification In 18/44 patients, lesions were seen on the corrected scan that were not seen (or were poorly seen) on the uncorrected studies. In 3/44 patients, lesions were seen on the uncorrected studies that were not seen on the corrected studies. Recommend reviewing both uncorrected and corrected images.


ADVANTAGES OF FDG :ADVANTAGES OF FDG Capability to detect unsuspected mets distant from original location With fusion of MRI & CT/FDG studies, greater accuracy can be accomplished in preliminary diagnosis = cost effective management of disease


Radiolabeled Sugars :Radiolabeled Sugars There is increased sugar utilization in many tumors An inability to metabolize deoxyglucose retains FDG longer than normal sugars Lung cancer, breast cancer, melanoma, and colon cancer all show increased sugar uptake How to label a sugar without changing its properties?


Radiolabeled Sugars :Radiolabeled Sugars The best label to date is fluorine-18 The compound of choice is fluorodeoxyglucose FDG behaves like glucose Has a tightly bound radionuclide Rapid tumor uptake


WHY DO PHYSICIANSORDER FDG STUDIES? :WHY DO PHYSICIANSORDER FDG STUDIES? Evaluation of pulmonary nodules Detecting, monitoring, and staging of cancer Post-therapy evaluation of disease


GLUCOSE PARAMETERS :GLUCOSE PARAMETERS Have patients refrain from any sugar intake post injection Allow adequate time to adjust glucose levels in cardiac patients using insulin or glucose, as appropriate. Ideal range: 90-130 mg/dl Diabetics are allowed to have a light meal up to four hours before their appointed time


PATIENT POSITIONING :PATIENT POSITIONING Perfect centering of target organ is critical for counting efficiency Pillows and other positioning devices may be used to immobilize patient and to maintain patient comfort Patient motion is prohibited during the emission and transmission studies to prevent imaging artifacts


QUALITY CONTROL :QUALITY CONTROL Adequate time must be allowed to perform quality control testing to ensure consistency. Includes Tc-99m flood, emission and transmission floods Flood data from both the emission and Attenuation Correction sources should be analyzed


ACQUISITION PROTOCOL :ACQUISITION PROTOCOL STUDY TIME/STEP FOV Brain 80 sec/azimuth 38 cm2 /center Cardiac 60 sec/azimuth 38 cm2/center Whole Body 40 sec/azimuth Full Field


Slide 44:RAW DATA TRANSMISSION


PROCESSED CORONAL SLICES :PROCESSED CORONAL SLICES


PROCESSED SAGITAL SLICES :PROCESSED SAGITAL SLICES


PROCESSED TRANSVERSE SLICES :PROCESSED TRANSVERSE SLICES


KNIT DATA :KNIT DATA


Clinical Cases :Clinical Cases Normal case Cardiac uptake Minimal diffuse abdominal uptake


Clinical Cases :Clinical Cases 50-year-old female with left rib pain X-rays negative Bone scan shows spine lesions Breast biopsy shows cancer Are there other lesions?


Clinical Cases :Clinical Cases 80 year-old-male with relapsed non Hodgkin's lymphoma CT shows an abnormal kidney and one enlarged left inguinal node FDG shows more extensive disease


Clinical Cases :Clinical Cases 62-year-old female with squamous cell tumor of the head and neck Completed course of radiotherapy MCD study done to check for residual disease Uptake seen in the lung


Clinical Cases :Clinical Cases 36-year-old female post-op colon cancer CEA rising CT shows possible pelvic mass FDG performed to assess the likelihood of tumor


Clinical Cases :Clinical Cases 47-year-old female with recurrent colon cancer CT shows a mass in the head of the pancreas and no other definite disease MCD study performed to see if curative surgery was possible


Clinical Cases :Clinical Cases 56-year-old male with pulmonary metastasis from colon cancer Being considered for curative resection CT of abdomen shows post surgical changes and questionable nodes


Slide 68:Artifact/ Injected in the Light


Slide 69:ARTIFACT/MUSCLE UPTAKE


ARTIFACT/ INJECTION SITE :ARTIFACT/ INJECTION SITE


ARTIFACT/ HIGH COUNT RATE :ARTIFACT/ HIGH COUNT RATE


Clinical Case :Clinical Case 50-year-old female with left rib pain X-rays negative Bone scan shows spine lesions Breast biopsy shows cancer Can we follow disease with FDG?


Slide 74:Corrected Uncorrected


Slide 75:Corrected Uncorrected


Clinical Cases :Clinical Cases One year post therapy with Tamoxifen Radiation therapy to T-12 to L-2 Treated with bisphosphonate Repeat bone scan and FDG


Clinic Cases :Clinic Cases 18 months post diagnosis Bone scan shows new neck lesion No change in thoracic and lumbar lesions on bone scan FDG shows tumor recurrence at previously radiated site Therapy changed


Slide 81:Pre RX Post RX 18 months later


Clinical Cases :Clinical Cases 29 year-old female with an axillary mass Biopsy compatible with breast cancer Mammogram negative Ultrasound negative


Slide 83:Corrected Uncorrected Corrected


Cardiac Applications :Cardiac Applications Detects viable, but hypoperfused myocardium Hibernating myocardium Blood sugar must be between 90 and 130 mg% May require sugar or insulin to adjust


Slide 87:Attenuation Correction No Attenuation Correction Attenuation Correction No Attenuation Correction


Radiation Dosimetry to Patient :Radiation Dosimetry to Patient FDG is ultra-short half-life Whole body and bladder dose similar to bone scan About 2 to 3 rads whole body


Conclusions :Conclusions FDG gamma camera coincidence imaging is feasible in a routine nuclear medicine lab Gamma camera FDG studies provide additional diagnostic information Attenuation correction improves both visual and diagnostic quality of FDG images


MCD Future :MCD Future Validate utility in various disease states Demonstrate cost/benefit Continue to develop clinical protocols Increasing number of units in the U.S. In 1995, there were 60 PET units today over 500 coincidence devices Increased Integration with CT and MRI