This the first part of technologist teaching Series.

1. PET/CT Variants and Recommendations for
patient preparation.
2 9 D E C E M B E R , 2 0 2 2
Miad Alsulami .MD.FRCPC
Technologist
Teaching Series

2. OUTLINES:
• Positron Decay.
• Attenuation Correction.
• Factors affecting SUV measurements.
• The role of Delayed Imaging.
• FDG PET Biodistribution.
• Affect of Serum Glucose on scan Quality .
• FDG-avid BAT.

3. FDG PET Scan
Positron-emitting radionuclides are produced in cyclotrons.
These radionuclides have an excess numbers of protons and decay via the emission of positrons =n +
positron + energy.
Positrons ( Positively charged electrons) lose kinetic energy and combine with an electron.
An annihilation reaction that generates 2 photones (511keV each) emitted at 180 degrees from each
other.

4. Attenuation Correction
• Attenuation is the loss of photons by absorption in the body or scatter out of the detector field of
view.
• Common methods for attenuation correction include:
1. Calculated correction based on assumptions of body contour
2. Measured correction using transmission data: CT or 68Ge/68Ga

5. 18F-FDG Uptake
• 18F-FDG is a glucose analog .
• Increased glucose uptake can be related to activity of malignant tissue .
• Glucose transporters transfer glucose & FDG into cells where phosphorylated by hexokinases
occurs.
• Phosphorylated FDG cannot be rapidly metabolized and is trapped in proportion to glucose
metabolism.

6. SUV
• standardized uptake value.
• SUV = Mean ROI activity (mCi/mL)/ [Administered activity (mCi)/ body weight (g)].

7. Factors affecting SUV measurements
• Factor Effect on SUV
1. Plasma glucose -Lower SUV with higher blood glucose.
2. FDG dose infiltration -Lower SUV.
3. Time after injection -Higher SUV with longer uptake period.
4. ROI definition -Lower SUV for larger regions.
5. No decay correction of injected dose-Lower SUV.

8. Delayed Imaging
• Plateau in18F-FDG uptake by tumours occurs ~ 45 minutes after injection.
• Optimal tumor-to-background ratio occurs at 2-3 hours following injection.

9. • Delayed imaging can be helpful in assessing pathology.
The focal 18F-FDG in the right
lower pelvis disappeared on
delayed imaging, in keeping with
physiological activity .

10. FDG PET Biodistribution

11. The Heart
• 18F-FDG cardiac uptake is variable.
• The primary substrate for myocardium is fatty acids.
• To suppress physiologic myocardial activity : long fasting hours (16-18 hour , high fat ,high fat ,low
carb diet , and optional heparin injection).
• Suppression needed in ( infected myocarditis and sarcoidosis )

12. The Breasts, Uterus & Ovaries
Bilateral Brest uptake : postpartum ,
lactation or pregnancy . Normal In premenopausal women .

13. Tracer uptake in the Liver & Spleen

14. Whole Body FDG PET: Patient Preparation
• Exercise should be avoided for 24 hours prior to the study.
• Fast for 4-6 hours prior to the study.
• Blood glucose level should be confirmed:< 120 mg/dl preferred, up to 200 mg/dl may be
acceptable
• Diabetic patients: no standardized protocol.

15. Uptake in Skeletal Muscle
• Uptake in skeletal muscle is usually linear & symmetric, or diffuse.
• Increased with activity and elevated insulin level.

16. Skeletal muscle uptake
due to difficulty breathing
Skeletal muscle uptake
due to hyperinsulinemia
Skeletal muscle uptake
due to weightlifting
Reference :SNMMI review course

17. Rhabdomyolysis
Literature review: case report on
Rhabdomyolysis and FDG PET
Sheehy N, Israel DA. Findings on
(18)FDG-PET imaging in statin-
induced rhabdomyolysis.
Clin Radiol. 2007; 62(10):1012-1014

18. Affect of Serum Glucose
Blood Glucose 93mg/dL Blood Glucose 317 mg/dL Blood Glucose 97mg/dL

19. FDG-avid BAT
Usually multi-focal & symmetric
Thought to increase with exposure
to cold and/or anxiety
Consider patient warming, diet
and/or medication

20. Room Temperature Control and Blankets
Prior to warming Post-warming

21. • Warming patients at a constant 24C for half hour prior to until 1 hour following tracer
administration reduced FDG-avid BAT from 9% to 27%.
• This was most effective in the summer and winter.
Zukotynski et al. J Nucl Med Mol Imaging. 2010; 37: 1854-60Garcia et al. Mol Imaging Biol. 2004; 6: 368-72, Garcia et al. Mol Imaging Biol. 8: 24-9 & Christensen et al. Clin Nucl Med.
2006; 31: 193-96 showed that 24oC & extra blankets significantly reduced FDG uptake in BAT

22. Diet or Medication?
• High-fat, low-carbohydrate diet.
• Propranolol :Parysow et al. Clin Nucl Med. 2007; 32(5): 351-357 showed 20 mg oral propranolol
given 60 minutes prior to FDG administration significantly reduced FDG-avid BAT in adults.
• Fentanyl: Gelfand et al. Pediatr Radiol. 2005; 35: 984-990 showed 0.75-1.0 "g/kg iv fentanyl given
10 minutes prior to FDG administration reduced FDG-avid BAT from ~ 26% to 7%.
• Diazepam.

23. Why Do We need to stope certain
medications before PET CT ??
• Chemotherapy: (2-4 weeks) , to prevent false positive results .
• Steroid : can affect blood glucose level and can lead to altered
biodistribution , Mask intracranial metastasis)
• Immunotherapy: Pseudoprogression.