PET-CT in Adrenal Tumors

PET-CT in Adrenal Tumors

Arman Hassanzadeh-Rad, MD

Nuclear Medicine Physician, Research Center for Nuclear Medicine,

 Shariati Hospital, Tehran University of Medical Sciences

Hybrid Imaging: PET-CT

• In hybrid PET-CT imaging ,CT is used for two different purposes:

1- Attenuation Correction: Each 511 KeV photon passes through tissues with variable tissue densities (from bone , to soft tissues and lung). This interaction of photon with material (through Compton scattering and photoelectric processes) decreases photon intensity. CT gives attenuation coefficients of different tissues (and an attenuation map) and corrects the amount of intensity which has been decreased because of the attenuation (initial photon intensity is more than non-attenuation corrected photon intensity)

2-CT is used for anatomical localization: although CT applied in PET-CT is non-diagnostic low-dose CT( tube current= 30 mA),it still can be used to roughly find out anatomical locations in neck, chest, abdomen, pelvis and extremities. However; the interpreter should examine “Registration” of PET images with CT images.(i.e bladder activity should be precisely matched with anatomical location of bladder). In most instances, PET and CT images are automatically fused. If not, one should manually shift organ’s activity (in this case bladder) to match anatomical location of that organ. Usually by precise fusion of one organ’s PET and CT images, other regions will be matched simultaneously.

Standardized Uptake Value (SUV)

• SUV is a semi-quantitative parameter to measure amount of uptake in a region.
• SUV is defined as:[mCi/ml(decay corrected) in tissue] /mCi injected/body weight in grams
• If tissue density is assumed 1 gr/ml, SUV will be dimensionless.

SUV

• Severel methods to express SUV:

• SUV max: pixel with maximum SUV throughout the whole Region of Interest (ROI)
• SUV mean: average of SUV in the hottest 4 * 4 pixels
• SUV adjusted to lean body mass (SUL)
• SUV adjusted to body surface area (SUVbsa)