Nuclear medicine is a medical speciality that uses small amounts of unsealed radioactive materials to diagnose and treat diseases

• Attached to specific organs, bones, tissues
• Emit gamma rays that can be detected externally by special types of cameras: gamma camera or PET camera (positron emission tomography)

• Time
• Distance
• Shielding

• Radioactive decay: exponential

• Decay procedure

• Ideal physical props of radioactive substances:
• Readily available and cheap
• High specific activity
• Short t 1/2 (few hrs)
• For gamma camera imaging: decay by isomeric transition with mono-energetic gamma emission of approximately 150 keV

Distribution depends on

1. Radionuclide (eg. Iodine)
2. Carrier molecule (eg. DTPA, MDP)

Technetium-99 radiopharmaceuticals

1. Elution of generator and preparation in lab inside hospital

2. Unit dose (purchased on demand)

Other pharmaceuticals

1. Eg. Thallium-201, Iodine-131
2. Purchased on demand

• With shielding
• Inside is syringe with solution with contains radiopharmaceutical
• One generator can be used for 1w-10d

• Gamma camera or PET camera works in conjunction with computers used to form images that provide data and information about the area of body being imaged
• 0.01% of gamma radiation coming from Pt enters detector (most are absorbed by lead in collimator)
• Scintillator (sodium iodide): interacts with gamma radiation to produce visible light
• Gamma camera produces digital picture (c/f x-ray which produces analogue image)

• Need gas or aerosol for Pt to breathe in
• Particles produced are much smaller than aerosol, behaves like gas

• Calibrator: to measure dose
• Cupboard: to make doses yourself inside

Lead shielding: removes 99% of radiation to the operator's finger

Lead brick: put around storage

Forceps

Also

• Ga-67 gallium citrate
• Infection
• Tc-99m / In-111 WBC [labelled EBC]
• Infection

• Multiple hot spots compatible with multiple bony metastases
• [Half of tracer is excreted through kidneys to bladder, therefore can see these structures
• Wait 2-4 hours until scan, until tracer is excreted from soft tissues]
• Increased uptake - increased phosphate update - increased osteoblastic activity
• Bony reaction to presence of bony metastases
• Note: not seeing uptake by tumour cells; we are seeing increased bone formation
• It is sensitive but not specific
• X-ray: need change in 50% of BMD before changes can be seen
• Bone scan: changes can be seen earlier

• Only when we see abnormal changes in x-ray (eg. osteophyte) there will be increased uptake in bone scan. But if there is increased uptake in bone scan but normal x-ray, this indicates bony metastases

• Increased uptake in primary tumour and lung metastasis

• Need both bone scan and x-ray for definitive Dx

• Transverse linear uptake in the lumbar spine is characteristic of benign osteoporotic collapse

• Perfusion: flow of tracer inside Pt (immediate)
• Serial 4 sec images (tracer in descending aorta, kidneys, etc). Increased early uptake in perfusion phase
• Delayed bone scan: increased uptake in lumbar region - can make Dx of osteomyelitis in the region (increased early uptake and delayed)
• Sensitive but not specific (increased specificity with WBC scan)

• 15 ml blood from Pt, centrifuge, add radiopharmaceutical, suspend in Pt's plasma, re-inject into Pt
• Image distribution of WBC in Pt
• Diagram: mainly in spleen, BM
• If focus of infection, WBC will accumulate here

• Bone scan: increased phosphate uptake in # site due to bone formation
• WBC scan: concentrate in lower part of femur (doesn't accumulate at # site)

• # neck of left femur
• In undisplaced #, may not see # line clearly in x-ray
• Therefore, can use bone scan will be +ve in 1-2d (depends on phosphate uptake)

• Bone scan and X-ray
• Stress # in pelvis
• Difficulty to Dx in x-ray (area occluded by bowel)
• Bone scan: increased uptake in sacrum, iliac area

Uptake

• Actively transported into tissue by Na-K-ATPase
• 88% extraction in one pass through coronary circulation

Redistribution

• Different in clearance of thallium
• Normally perfused zones clear lying more rapidly than ischaemic areas

• Detection of CAD
• Prognostic of likelihood of major ischaemic event
• Post-Tx follow-up

Normal thallium scan: < 1% chance of major heart event in next 2 years

• Antero-apical reversible ischaemia
• Normal after 4 hours (exercise-induced ischaemia)

• Polar map display
• MI
• Both stressed and rest images are abnormal

• See ppt

• Vesicoureteric reflux
• UTI
• Previous obstruction
• Congenital malformation
• Non-compliant bladder
• Obstruction

• See ppt
• After can, give Lasix, if no obstruction tracer will be washed down to UB

• T 1/2 , 10min - no obstruction
• T 1/2 10-20 min - indeterminate
• T 1/2 > 20 min - significant obstruction

Not always true, but taught in classical textbooks

• Dilated non-obstructed pelvicalyceal systems

• Right renal artery stenosis

• Gives picture of renal cortical mass
• Picture shows right upper pole scarring
• 43-57% = normal differential renal mass of one kidney

• Horseshoe kidneys with hydronephrosis of left moiety
• Easy Dx in DMSA scan because you can see the horseshoe kidney
• Harder in US (spine obscures bridging part of kidney)
• Can also use DMSA to Dx ectopic kidney (this tracer is specific for renal cortical tissue)

• Uptake mechanisms
• Analogue of adrenergic blocking agent guanethidine
• Same uptake but not metabolised

Uses

• Phaeochromocytoma
• Neuroblastoma
• Carcinoid
• Medullary carcinoma of thyroid
• Other neuroectodermal tumours

These all take up catecholamines

MIBG is taken up but not metabolised

• Right phaeochromocytoma

• Extra-adrenal phaeochromocytoma

• Tc-99m MIBI for parathyroid adenoma (one gland hyperactive), parathyroid hyperplasia (more than one gland hyperactive)

• Tc-99m, Iodine-131, Idoine-123 (iodine used less because has both alpha and beta radiation)
• Thyrotoxicosis, thyroid nodule, congenital hypothyroidism, ectopic thyroid, carcinoma of thyroid

• Graves disease and Autonomous nodule
• Both cause thyrotoxicosis
• Graves: whole gland hyperactive (diffuse uptake - can see pyramidal lobe)
• Nodule: only nodule takes up tracer, other parts of gland don't take up

• Subacute thyroiditis
• Decreased uptake: due to thyroid gland damaged + negative feedback

• Cold nodule
• Palpate Pt and use tracer to show where nodule is

• Thyroglossal cyst and ectopic thyroid

• Bone scan and iodine-131 scan
• Iodine used to scan
• Bone metastases; can see bone metastasis (destruction of bone by metastatic ca thyroid causes bone reformation)
• Can only use iodine to image papillary carcinoma and follicular carcinoma of thyroid (other less-differentiated types of carcinoma thyroid cannot take up iodine)
• Use thyroid to treat this Pt
• Bone scan: uptake in pelvic region