Hybrid PET/CT

Flashcards about Hybrid PET/CT

What does PET stand for?

Positron emission tomography

What is the use of a PET scan?

Non-invasive method of gaining 3D functional imaging and a form of molecular imaging. Can detect changes in tissues at a molecular level before structural changes can be observed on anatomical imaging

What are the indications for PET scans?

Oncology, infection/inflammation, neurology and cardiology

What is the rationale of PET?

PET relies on the administration of positron-emitting radiopharmaceuticals (β⁺)

Name three Radiopharmaceuticals?

18F-FDG, 68Ga-PSMA, 68Ga-DOTATATE

Where does 18F-FDG accumulate in the body?

Areas with high glucose demand

Where does 68Ga-PSMA accumulate in the body?

Areas which express the PSMA receptor

Where does 68Ga-DOTATATE accumulate in the body?

Areas which express the somatostatin receptor

What is the physics behind PET imaging?

Co-incidence detection

What is the tube voltage of CT acquisition?

Tube voltage of 80 – 120 kVp

What is attenuation correction?

CT scan (or MRI for PET/MRI) is reconstructed into a map of attenuation coefficients - provides more accurate understanding of radiopharmaceutical distribution.

What are Standardised Uptake Values (SUV)?

Allow radiopharmaceutical uptake in a region of interest to be quantified

What is 18F-FDG?

18Fluorine (radioisotope) bound to FDG (Fluorodeoxyglucose)

What is 18F-FDG a analogue of?

Glucose analogue

What happens when 18F-FDG enters the cells?

Taken into cells and phosphorylated by same mechanism as glucose. Once phosphorylated cannot diffuse out so remains in cells. Does not enter glycolysis pathway. Accumulates in areas of high metabolic demand (increased glucose needs)

What are the patient preparation requirements before 18F-FDG?

Fasting for 4 – 6h prior (plain water okay), Withhold diabetic medications (e.g. insulin, metformin), Avoid strenuous exercise for 24h prior, Establish IV access, Measure blood glucose level (between 4 – 11mmol/L)

What is the dose of 18F-FDG?

185 – 444MBq

Uptake period upon intravenous (IV) injection of 18F-FDG?

Rapidly distributes through the body, Cellular uptake increases & background activity decreases, Primary route of clearance → kidneys, bladder, Optimal imaging time at 60 mins

What is the scan region for most clinical indications?

Vertex (or eyes) to mid thighs

What are the normal image appearances of 18F-FDG?

Brain, Kidneys, ureters and bladder, Liver, Bone marrow

What is brown fat?

Is a type of adipose tissue, Contains many more mitochondria than white fat, More vascular and has higher oxygen usage, Involved in non-shivering heat generation and regulating body temperature

Longitudinal uptake along the aorta and the large vessels is pathognomonic for what?

Giant cell arteritis

What are some Image variants and artefacts?

Insulin, Metformin, Exercise, Respiratory motion, Patient movement, Physiological muscle uptake

What is Prostate Specific Membrane Antigen (PSMA)?

Transmembrane protein

Where is Prostate Specific Membrane Antigen (PSMA) normally expressed?

Epithelium of secretory ducts in benign prostate tissue

What are the clinical indications of 68Ga-PSMA-11?

Diagnosis, Staging, Monitoring therapeutic response

What is the dose of 68Ga-PSMA-11?

1.8 – 2.2 MBq/kg

What are the normal PSMA image appearances?

Lacrimal gland, Parotid gland, Submandibular gland, Sublingual gland, Nasal mucosa, Vocal cords, Liver, Spleen, Small intestine/colon, Kidneys/bladder

What is 68GA- DOTATE?

DOTATATE binds to somatostatin receptors

Name some Neuroendocrine tumours?

Carcinoids, Gastrinoma, Insulinoma, Pituitary tumours, Paraganglioma, Pheochromocytoma

What are the clinical indications of 68GA- DOTATE?

Localise primary tumours and detect sites of metastatic disease (staging), Follow-up patients with known disease to detect residual, recurrent or progressive disease (restaging), Determine SST receptor status visually and by using SUV

What is the dose of 68GA- DOTATE?

2MBq/kg of body weight to a max of 200 MBq

What are the Normal 68GA-DOTATE image appearances?

Pituitary gland, Salivary glands, Spleen, Liver, Kidneys/Bladder, Adrenal gland, Thyroid, Stomach and bowels

What is the difference between 18FDG and 68GA-DOTATE?

A combination of 18F-FDG and 68Ga-DOTATATE imaging can be used to evaluate the molecular profile of the disease.

Use of PET CT in paediatrics?

18F-FDG for oncology or neurological indications (e.g. epilepsy), 68Ga-DOTATATE for oncology (NETs), 68Ga-PSMA-11 very rarely used in paediatrics

What are the Image appearances of 18F-FDG in Paediatrics?

Thymus uptake, Epiphyseal plates of long bones, Increased likelihood of brown fat, Increased laryngeal muscles if talking or crying

What are the Image appearances of 68Ga-DOTATATE in Paediatrics?

Epiphyseal plates of long bones

What is the purpose of PET CT for RT planning?

PET/CT scans can provide invaluable information regarding the molecular behaviour of a tumour