Nuclear Medicine

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Nuclear medicine

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 uses medical isotopes to map physiology and pathophysiology in human body
 also known as functional or molecular imaging
 synergistic with Radiology which displays anatomy
 70 year history and recent rapid growth due to convergence technologies such as PET-CT.

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Radiopharmaceutical

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= isotope + ligand
localises in target organ, or target pathology
radiopharmaceutical = isotope + ligand
emits gamma rays
detected by gamma camera or PET camera with or without CT

eg
Tc99m bisphosphonate (eg HDP) for bone scan
Tc99m MIBI: cardiac perfusion scan
Tc99m MAA: lung perfusion scan
Tc99m ECD: brain perfusion scan
F18 FDG: PET tumour scan
Ga68 Octreotide: neuro-endocrine tumour scan

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PET/CT scan

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Medical Isotopes

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“Tracer Principle” allows exploration of basic functions

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Permits evaluation of:
1.regional blood flow of various molecules
2.metabolism within tissues
3.function of organs
4.intra- and intercellular communication
Maps physiology and pathophysiology

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Molecular medicine and neurology

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1.Epilepsy
2.Dementia
3.Tumours
4.Parkinson’s disease
5.Brain death

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Epilepsy

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Ictal and interictal 99mTc-HMPAO and 99mTc-ECD for brain perfusion evaluation: increases in regional cerebral blood flow because of seizure propagation and increased neurotransmission and synaptic activity

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Dementia

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Potential molecular targets: neuroreceptors / tau protein / neuro-inflammation / beta oligomers

Hypometabolism of temporal, parietal lobes, precuneus and posterior cingulate
Similar changes with brain perfusion agents (99mTc-ECD, HMPAO)
Scans can document improvement in perfusion + metabolism with treatment (eg Donepezil, eg Acetylcholinesterase inhibitor)

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Tumours

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gliomas are inflitrative and not all areas are the same grade so need to knwo where to biopsy

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Parkinson’s disease

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PK assesment of Status

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Assessment of status using:
1.Dopamine synthesis – 18F-DOPA
2.Dopamine transporter – 123I-β-CIT
3.Dopamine receptor – 123I-IBZM

IMAGE: shows loss of DA metabolism in Basal Ganglia

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Brain death

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Absence of blood flow to anterior and middle cerebral artery territory
Implies cellular death

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Gastroenterology applications

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Function of oesophagus, stomach, small bowel and colon.
Liver: masses, function
Spleen: function
Gastrointestinal bleeding, protein loss
Gallbladder: function, inflammation

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oesophageal function

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Common upper GI symptoms: dyspepsia, upper abdominal pain + distension, satiety occur in up to 20% of population
Suspected oesophageal disorder: use OGD, barium swallow/CT to exclude anatomic lesion and gastric path
Oesophageal transit studies can measure transit. Up to 50% of people with dysphagia and normal barium studies: have dysmotility.

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gastric function

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Gastroparesis can cause nausea, vomiting, distension
50% have no obvious cause on anatomic studies
Functional assessment is important
Assessed using radiolabelled solid meals such as eggs, pancake
Measures gastric emptying: solid + liquid

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small/large bowel transit

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Therapy for chronic constipation depends on cause
a)irritable bowel syndrome
b)slow colon transit
c)pelvic floor dysfunction
d)many others
Use 67Gallium citrate

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liver

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Liver tumours occur commonly
a)malignant-metastatic/primary hepatocellular carcinoma
b)benign-haemangioma, adenoma, focal nodular hyperplasia, cysts, fat sparing, fat infiltration, others
Radioligands used:
a)18F-FDG glucose analogue: increased uptake in most malignant processes
b)99mTc-red blood cells: used for haemangiomas
c)99mTc-heat denatured red blood cells: splenic tissue
d)99mTc-sulfur colloid: used for liver function (RES)
e)99mTc-HIDA: used for hepatocyte function, biliary excretion and gall bladder function

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Liver Metastasis (colorectal cancer)

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still curable

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Hepatic haemangiomas:

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a)common benign tumour of the liver
b)up to 10-12%
c)more common in women
d)often asymptomatic
e)cause diagnostic dilemma
Cluster of capillaries: accumulate red blood cells

haemangiomas display delayed bloodpooling because of large venous capacitance: characteristic appearance

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BILIARY SCAN

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Equivocal US – does the patient have acute cholecystitis?
Chronic abdominal pain – does the patient have chronic cholecystitis or biliary dyskinesia?
Other – post cholecystectomy surgical complications (eg biliary leak), neonatal jaundice

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THYROID GLAND

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99mTc pertechnetate uptake shows “iodine trapping” function, while ultrasound sounds shows size, shape and presence of nodules

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Thyroid single hot nodule

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single hot nodule = toxic autonomous adenoma, as a cause of hyperthyroidism

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Diffuse Increased trapping function in thyroid scan

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Graves’ disease as a cause of hyperthyroidism
- ALMOST NO background uptake left

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sub-acute thyroiditis

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sub-acute thyroiditis: thyroid hormone release due to gland inflammation (post viral usually). Common cause of hyperthyroidism

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Single cold nodule

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cold nodule  20% chance of malignancy
cardiac MIBI scan: abnormal focus in Rt thyroid 99mTc scan: single cold nodule

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Fine needle thyroid

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HYPERPARATHYROIDISM

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“stones, moans and broken bones”
typically raised serum Ca level with measurable serum PTH
usually sporadic (parathyroid adenoma)
sometimes secondary to renal failure
investigation to assist surgeon locate glands (neck/chest) to allow minimally invasive surgery
ultrasound, MRI, CT used
Nuclear Medicine most sensitive
early-delayed MIBI (sestamibi) scan or MIBI subtraction scan

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Parathyroid Scan

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parathyroid MIBI scan showing early uptake and delayed washout from the parathyroid adenoma behind the lower pole of right lobe of thyroid

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ADRENAL GLAND

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small masses common
adenoma: 1-5% incidence
some adenomas are hormonally active eg cortisol secreting
common site for metastases
adrenal “incidentalomas” common – need Ix

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adrenal gland: Anatomy
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ADRENAL TUMOUR

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adrenal adenoma

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Phaeochromocytoma

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Arise from the adrenal medulla
Hypertension-chronic or intermittent; headache; palpitations; sweating; subclinical-incidental
Diagnosis important: high mortality in undiagnosed subjects undergoing surgery or anaesthesia
High sensitivity of both 123I-MIBG and 111In-octreotide

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neuroendocrine: Tumours

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Neuroendocrine tumours: arise from adrenal medulla, sympathetic nerve chain, pancreas, gastrointestinal tract and skin
Carcinoid tumour:
a)usually arise from pancreas or lower small bowel
b)metastasise to liver, classic triad of diarrhoea, flushing and asthma
c)secrete excess 5-hydroxytryptamine (serotonin)  urinary 5-HIAA 95 hydroxyindolacetic acid = metabolite of serotonin
Express somatostatin receptors
Imaged with 111In-octreotide, occasionally 18F-FDG PET

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Carcinoid tumours

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therapy: Applications

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Radionuclide therapy is possible with appropriate compounds:
1.177Lutetium-octreotate: uses β energy (neuroendocrine tumours)
2.131I-lipiodol – uses β energy (liver cancer)
3.90Yttrium microspheres: uses β energy (liver cancer)
4.131I – uses β energy (thyroid cancer)
5.131I – uses β energy (various causes of hyperthyroidism)

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Radioiodine ablation

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Radioiodine ablates residual thyroid tissue post surgery, reduces risk of local recurrence and improves survival