Patient Preparation for PET Imaging

Welcome to the Patient Preparation for PET Imaging Web Based Training By the end of this course, the attendee will be able to: State the fundamentals of PET physics, instrumentation and image formation. Describe the concept of attenuation correction with CT List the steps for preparing patients for PET oncology imaging List the steps for preparing patients for PET cardiac imaging List the steps for preparing patient for PET Neurology imaging Neutron deficient isotope is unstable Positron is emitted Positron (e+) meets electron (e-): annihilation Emission is in a straight line 511 keV Gamma ray 511 keV Gamma ray Line of Response Crystals Crystals Blocks Blocks Sinograms (PET Raw Data) Images SPECT Different isotopes having different gamma photon energies PET Different isotopes, but same gamma photon energies Tracers emit a single gamma photon Tracer emits a single positron that creates two gamma photons Photon contributes to the image if it falls within a specific energy range Photons contribute to the image if they fall within a specific energy range AND fall within a timing window (coincidence) True Events Scatter Events Random Events Occurs from the same annihilation event Strike the detectors wihin a coincidence timing window Strike the detectors at 180 degrees Considered "valid" events Occur from the same annihilation event Strike the detectors within a coincidence timing window Do NOT strike the detectors at 180 degrees due to deflection or attenuation  Do NOT occur from the same annihilation event.  Do NOT strike the detectors within a coincidence timing window.  Strike the detectors at 180 degrees, but originate from two separate annihilation events Scatter Events Scatter is patient geometry dependent and can exceed 50% of the count rate Reduces image contrast Reduces image accuracy Solution: Measure and correct it using statistical simulation algorithms. With Scatter Correction Without Scatter Correction Random Events Randoms are specific activity dependent and can equal or exceed true events Reduces image contrast Reduces image accuracy Solution: Measure randoms using a delayed coincidence timing window to subtract these events from the data With Randoms Correction Without Randoms Correction Noise Equivalent Count rate (NEC) is a measure of: Signal-to-noise ratio True counts acquired over a range of activity. For larger patients, increase imaging time for PET rather than increasing prescribed radioisotope dosage Attenuation Loss of an event due to scatter or absorption Reduces appearance of deep lesions Reduces quantitative accuracy (No SUV) Solution: Measure attenuation with a CT scan during the acquisition. Uncorrected Corrected How much attenuation is there? In water (soft tissue), half of the photons are lost every 7.2 cm (2 7/8 inches) When patients are imaged in the arms down, the lateral projection data is 25% of what it would be if the patient was imaged arms up. PET Raw Data Randoms Correction Scatter Correction Attenuation Correction Filtering and Reconstruction Creation of the AC File: Typical dedicated PET transmission file employs rotating 68Ge rod sources Each bed position acquires both emission and transmission data. Time consuming (typically ¼ to ½ of total imaging time of an hour or more) Densities saved as µ values and then segmented into air, bone, and tissue density groups Creation of the AC File: CT images transformed into attenuation image µ density values at an estimated effective CT energy, typically 80 keV. Attenuation image multiplied by the ratio of attenuation coefficients of water at that same effective CT energy to the PET isotope emission energy of 511 keV. Original CT Images (Inverse Grayscale) Attenuation Ratio Scaled CT Images  Increased statistical quality  Increased spatial resolution  Much faster acquisition time The Old The New! (A) Contrast-enhanced CT clearly depicted lesion (arrow) in right liver lobe. (B) PET imaging was found to be negative for malignant disease. (C) Diagnosis of metastatic disease was based on CT data when evaluating fused images. Metastatic disease to liver was proven by histopathology. Fluorine is a halogen element (“salt former”; non-metallic) Created from proton bombardment of enriched 18O water in a cyclotron Decays back to stable 18O F18 ► O18 + E (β , v) Hydrogen analog 109.771 minute T ½ Na18F Introduced as bone imaging agent in 1962. FDA approved bone imaging in 1972 FDA approved for PET bone imaging in 2000 for evaluation of altered osteogenic activity. Historically not used as often due to isotope cost and availability compared to 99mTc phosphate agents Excellent specificity and sensitivity for bone scanning. High spatial resolution ~ 2 – 5 mm Favors uptake: Axial over appendicular skeleton Joints over shafts of long bones High bone-to-background ratio due to rapid blood clearance Fluorine is directly incorporated into the bone matrix unlike 99mTc phosphate agents which adhere to bone by chemical absorption Tracer uptake is approximately twice as high as 99mTc phosphate agents, Shorter post-injection waiting period prior to imaging No patient preparation needed Typical injection dose:  ~10 mCi After injection, continue to hydrate with water and/or IV saline Imaging 60 – 90 minutes post injection Pitfalls Tracer uptake in benign bone lesions Tracer uptake in DJD of bone & joints Difficult to interpret “superscan” due to diminished renal and soft tissue activity Commonly used in PET imaging Glucose analog Formula - C6H11FO5 Fed State Glycolytic pathway active Using glucose for energy Fasted State Glycolytic pathway inactive Using fatty acids for energy Myocardial and Muscle Tissue FDG Uptake will be more prevalent in the Fed State Heterogeneous populations of cells Most not regulated by presence or absence of insulin Higher use of glucose compared to non-cancerous cells Easily identifiable in PET imaging Check on the patient’s insurance status. Are they covered by: Private insurance Medicare Medicaid Are the indications for the study qualify for coverage? Check CMS website for latest updates See the scanner prior to scan or provide a detailed description of the scanner. Anti-anxiety medications Explain the entire process of the procedure including amount of time to be spent in the scanner Communication is vital for these patients Female Patients: Pregnancy status Menstrual status Menstruation may show increased uptake in uterus Lactation Increased update in breasts Have mothers pump before injection Should have enough to sustain child for 18 to 24 hours. Wait at least 1 month after last treatment before follow up scan Imaging too soon can result in: False negative imaging results Flare phenomenon (high bone uptake) Can also be observed with patients on immunosuppressants Exception: Documentation of effectiveness of chemotherapy treatment Suggestions: Not recommended immediately following treatment. Inflammation Wait 3 to 6 months Exception: Immediate imaging can be performed if the referring physician is only concerned about distant metastasis. Disordered metabolism typically due to decreased circulating insulin levels FDG uptake can be impaired due to diabetic hyperglycemia Patient’s blood sugar levels should be under control by diet or medication. Non-diabetic normal fasting range:    70 – 99 mg/dL Diabetic range: 125 mg/dL or higher Type 1 Diabetes: Schedule in the A.M. PET study can be started 2 hours after administration of insulin. Type 2 Diabetes: Schedule in the P.M. Patients can eat and take medications in A.M. Fast for 4 hours. Ideal serum glucose level is 70 – 120 mg/dL   Recommended fasting time: 6-12 hours Minimum of 4 hours Water and daily medications can be taken Fasting reduces circulation levels of insulin and glucose Reduces uptake in myocardium and muscle tissues Inpatients: Discontinue IV lactose or dextrose infusions during fasting period. Diabetics: Refrain from taking insulin or other diabetic medications for at least 2 hours prior to exam. (with physician consent. Discontinue several hours prior to appointment Reduces myocardial glucose uptake Patients should be well hydrated prior to exam. 48 oz. of water the day before 24 oz. of water the day of Facilitates better FDG uptake Increases FDG clearance from non-target tissues Lowers radiation dose to the patient Reduces tracer concentration artifacts Refrain from exercise and strenuous activity 24 hours prior to scan. Limits muscle uptake of FDG. Post activity, muscles use glucose to replace glycogen stores Athletes should refrain from training up to 72 hours prior to scan Make sure scanner is in working order before injecting patients. Good QC Bad QC Any recent biopsies or surgeries? Any recent imaging procedures performed? Any oral contrast recently? General medical history (coughing, bronchitis, pneumonia) Observe the patient and take note of any medical issues that can be seen. Weigh the patient Most newer Biograph scanners have a table weight limit of 500 lbs. Do not exceed recommended table weight limits. Make sure patient’s girth does not exceed the bore size. Biograph Bore Sizes: Biograph Horizon: 70 cm Biograph mCT: 78 cm Accurate weight = accurate SUV measurements   Know the patient’s BGL > 150 to 200 mg/dL, reschedule the patient Inject using IV or butterfly needle Follow with 20 – 30 mL saline flush Typical adult FDG dose: 5 - 10 mCi After injection, assay syringe and IV for residual dose. Make sure to enter the dose in patient protocol. Keep patient warm and comfortable Keep patient calm and quiet to minimize muscle uptake No reading, playing video games or walking around Diuretics are sometimes recommended Helpful for evaluating pelvic lymph node activity Hypermetabolic lesions in bladder wall Depending on the indication, the typical uptake period is 60 to 90 minutes Empty bladder Head and neck malignancies Swallow water Rinse mouth Position patient comfortably on the scanner table to reduce incidences of motion artifacts. 13NH3 Cyclotron produced Half-life: 10 minutes Energy 1.19 MeV Advantages: Exhibits rapid blood clearance Can perform exercise testing Bolus injection Relatively high uptake retention (~83%) Quantification (CBR) Disadvantages: Cyclotron produced Longer T1/2 Decreased throughput when compared to Rb82 High initial cost Marked lung uptake in smokers Low uptake in lateral/posterolateral wall in some normals Excess lung and liver uptake in some patients 82Rb Generator produced Half-life: 75 seconds Energy: 3.35 MeV Advantages: K+ analog Generator produced Lower cost than 13NH3 Short T ½ (75 seconds) High throughput capacity Repeat scans quicker Low technologist exposure Disadvantages: Administered as a long infusion, no bolus. Higher monthly costs Higher energy 3.35 MeV Lower resolution Scatter from 700 keV gamma 3rd particle (10-15% total activity) Lower uptake and retention than NH3 Image quality affected by: BMI Pulmonary HTN LVH Can only do pharmacologic stress Image quality declines over generator life Cyclotron Produced Half-life: 110 mins Energy: 0.6335 MeV PET/CT Imaging Offers: Higher specificity Easier to diagnose 3 vessel disease Always has attenuation correction Non invasive way to calculate MBF and CBF reserve. Better spatial resolution Increased count statistics Reasons for Ordering SPECT MPI: PET/CT scanner not available Likelihood of CAD is low (PET normal) Likelihood of significant CAD high Angioplasty is almost certain Crucial to correlate exercise symptoms with simultaneous imaging Women Breast implants Bariatric patients Chest wall deformity Inconclusive SPECT study Why PET Myocardial Viability Scanning? Permanent damage vs. Viable heart muscle tissue. Determines if heart can recover if blood supply is restored. FDG – form of glucose Heart has to demonstrate ability to metabolize glucose Permanent damage No glucose metabolism No benefit from revascularization 35% of bypass or angioplasty patients do not show improvement in cardiac function. No Permanent Damage Heart able to metabolize glucose Possible benefit from revascularization Glucose loading time consuming and can cause scheduling delays NPO for 4 – 6 hours No caffeine for 24 hours No nicotine for 6 hours No beta blockers No calcium channel blockers No theophylline derivatives for 48 hours Cardiac History Documentation Symptoms Cardiac Events NPO for 6 hours Caffeine and Nicotine Can affect pharmacological stress medication and should be discontinued 24 hours prior to exam. Smoking can affect CBF reserve and should be discontinued 6 hours prior to exam. Medications that can affect pharmacological stress agents: Nitroglycerine compounds Theophylline Beta Blockers Calcium channel blockers Breast Feeding Stop before injection of tracer. 13NH3 Ammonia – Wait 5 hours before resuming 82Rb – Can resume when patient returns home Cardiac Metabolism Facts: Perfusion, contractility and metabolism are closely interrelated Fasting heart will metabolize fatty acids Glucose-loaded state heart will metabolize sugar Ischemia Low perfusion Myocardial cells shift from fatty acid to glucose metabolism Cardiac History Documentation: Symptoms Cardiac Events Determine if Patient is Diabetic Check medications being taken to control BGL. Type and dosage may play role in decision how the manage BGL during procedure. Patient should be fasting for 6-12 hours Check blood glucose level (BGL) If BGL is <250 mg/dl, administer oral glucose of 25-100 g If BGL is >250 mg/dl , no glucose loading necessary Proceed with insulin administration. (See next slide) Administer 5-15 mCi of FDG if BGL is <150 mg/dl Guidelines for Blood Glucose Maintenance After Oral Glucose Administration BGL at 45-90 mins after Administration Possible Restorative Measure 130-140 mg/dl 1 unit of regular insulin IV 140-180 mg/dl 2 units of regular insulin IV 160-180 mg/dl 3 units of regular insulin IV 180-200 mg/dl 5 units of regular insulin IV > 200 mg/dl Notify physician IV Glucose Loading Protocol Patient should be fasting 6 to 12 hours prior to the procedure. Check blood glucose level (BGL) Fasting BGL is < 125 mg/dl, administer 125 g D-50-W. Add 20 mg Hydrocortisone to D-50-W to minimize pain at injection site. Fasting BGL is between 125 and 225 mg/dl, administer 12g  D-50-W. Fasting BGL is >225 mg/dl, administer insulin using the following formula: (BGL-50)/25 After 30-60 minutes, if BGL is < 150 mg/dl, administer 5 to 15 mCi FDG intravenously. After 30-60 minutes, if BGL is > 150 mg/dl, administer more regular insulin until BGL is < 150 mg/dl before administering FDG. Uptake time is 45 to 60 minutes Normal fasting plasma glucose level of at least 6 hours. Dose: 5-10 mCi. Uptake: Patient should be resting Eyes closed Ears unplugged No physical activity Time: 20-60 minutes Conditions that can affect global levels of FDG distribution State of consciousness Sensory influences Anxiety Sedative drugs Overall uptake is affected, depending on sleep cycle Slow wave sleep: Global decrease in CBF Anxiety during REM phase: Increases CMRglc Avoid sleep during uptake periods Resting State No specific sensory stimulation No engagement in a behavioral or physical task. Quiet uptake area needed. Recommend eyes closed throughout procedure. Make patients familiar with surroundings prior to exam to avoid anxiety and restlessness. Not possible to control all patient’s mental functions. Global reduction in CMRglc and CBF Propofol Sevoflurane Isoflurane Halothane Increase in CMRglc and CBF Ketamine Related anesthetics Benzodiazepine Effects Most pronounced in the thalamus and occipital cortex. Opioids (Morphine and Buprenorphine) Reduces CMRglc Influence CBF and CMRglc Some will increase in certain areas of the brain Acetazolamide Adenosine You should now be able to: State the fundamentals of PET physics, instrumentation and image formation. Describe the concept of attenuation correction with CT List the steps for preparing patients for PET oncology imaging List the steps for preparing patients for PET cardiac imaging List the steps for preparing patients for PET Neurology imaging