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Procedure Guidelinesand Practical Applications For PET \CT ImagingbyDr. H. HawesaRAD 466-Lecture 7

1Advantages of PET :1- Better ( spatial resolution , quantitation) .2- Potential for labeling of biological compounds with positron emitters including C11 , N13 , O15 , F183-F18 flourodeoxyglucose (FDG) is the most commonly used radiopharmaceutical in all applications.

F18 flourodeoxyglucose (FDG):1-F18 is acyclotron produced radionuclide with a half-life of 110 minutes.2-integration of F18 into the Glucose molecule in position 2= F18-fluro-2-deoxyglucose.3-Behaves like a sugar4-Measures tissue metabolism ,which is enhanced in many tumors with significantly increased uptake compared to normal tissue25- F18- FDG is transported & phosphorlylated remains trappedin the cell6- Unlike glucise, this tracer does not undergo further significant enzymatic reactions.7- F18- FDG ,the accumulation of this compound is pe=roportional to glycolytic rate.

3Clinical Indications:1-Differentiation between benign & malignant tumors.2-Staging of cancer at the time of initial diagnose & after recurrence.3-Evaluation of the effect of therapy on cancer.4-Ptovided images of viable tumor distribution for target definition for optimal external beam radiation therapy.5- Cardiology & Neurology6- Whole body screening for cancer.4Patient preparation :1-Give instruction to the patient..2-Remove any metallic object that can cause attenuation artifacts3-NPO for 4-6 hr prior to scan (decrease insulin level)4-blood sugar level should be within reference range.5 -Non diabetic patient ( start scanning the morning after an overnight fasting.)6 -Diabetic patient can eat their usual breakfast & medication & they start scanning around noon.7- Avoid vigorous exercise for 24hr prior to beginning the study.8 - No interventions (surgery chemotherapy) within the last 1-2 months.9 -Muscle uptake should be controlled: A- Patient should lie still throughout the uptake period. B- Patient shouldnt talk ( to minimize the uptake in the laryngeal muscle.) C- Use muscle relaxant510 - Keep the patient warm during uptake period to minimize the uptake in brown adipose tissue (e.g: superclavicular & paraspinal regions)11 - Hydrate the patient with 1-2 glass if water12 - Sedation may be need for patient with claustrophobia.13 - patient should be screened for a history of iodinated contrast material allergy (in CT study.)14 - For brain imaging , patient should be in a quite & dimly lit room.15 - Blood glucose should be checked before FDG administration . (tumor uptake of FDG is reduced in Hyperglycemic states)16 - Arms should be elevated over head.17- FDG should be injected at a site contra lateral to the site of concern.6

PET scan procedure :1- Dose = 10-20 mci (370 - 740 MBq) of F18-FDG.2- Begin image acquistion = 45-60 minutes later.3-Scan acquisitions : A-Limited area scanning B-Dynamic imaging C- Whole body imaging D-Total body imaging4- 2D or 3D.5-Dedicated PET or PET/CT 6-Imaging time (E = 4-5 min/bed position)11Technical consideration :.1- The dose prior to dispensing2- The dose prior to injection(dispensing). A-Dont invert the lead pot & vial to withdraw FDG. B-Use of a long flexible needle (angled away from the top of the vial). C-Shielded long flexible needle D- Dose drawing system.12

Normal FDG scan:.1- Brain.2- Heart activity (varible).3- Kidney & the Bladder

Imaging Artifacts :Objects. 1- Metallic.2- Respiratory motion3- Contrast medium.4- Truncation.

Metallic Object:-e.g: Prostheses ,dental implants .- Currently, there are no clear methods for overcoming this14

Respiratory Atrifacts :CT = with breath hold at full inspirationPET= breathing normally- The anatomy of CT should match with PET images (If not = artifacts )

Solution :1-PET (no AC) & reviewed with PET (AC)2- Use of multislice CT3- Respiratory gating4- Correction algorithm5- Immobilization

AC= Attenuation correction17

Contrast Media:- Iodinated contrast used in CT to enhance attenuation values in the vessels (IV) & gastrointestinal tract GIT (oral)

Solution:-Perform two CT scans : 1-Clinical CT with CM. 2-CT for AC (non-contrast , low dose )-Use of algorithms to set the contrast - enhanced pixels to a tissue-equivalent value

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Truncation:1- Large patient. 2-patient with arms down.3-Several algorithms..4-Breast implant23

Cardiac viability .. Area of reduced myocardial blood flow in The anterior wall has visible tissue as illustrated by enhanced uptake of FDG .

Neurology application. . Dopamine receptor system is particularly useful in patients with movement disorders ( e.g. parkinsons disease ).

. Blood flow using O 15 labelled water .. MRI & CT.( replaced much of the brain studies , . SPECT .( recommended in the case of epilepsy)Radiation Protection . Fast & reliable technique .. L shield .. Dose to technologist.. Use of unit doses. . Minimize the time in dispensing .. Minimize the time handling of syringe.. Minimize the time spent with injected patient.. Use of cart to transport the dose from the hot lab to injection room .. Use of additional shielding in the injection room & waiting area .. Using long flexible needle & long handled forceps.Time distanceesshielding

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