Diagnostic radiology - Nuclear Medicine Flashcards
Most common radionucleotide?
Technetium-99m
Function of radionucleotide imaging?
Use radioactive isotopes-emitted ionizing radiation to assess organ function and structure
Detect changes in metabolism, blood flow, regional chemical composition
Difference between Gamma radiation and X-ray
Gamma rays have higher energy and penetrating power than X-ray
X-ray = photons emitted from electron orbits
Gamma rays = photons emitted from nucleus
Explain how a gamma camera works
1) Decay of radioisotopes (e.g. technetium-99m) releases ionizing radiation
2) Passage/ absorption of Tc99m photon in collimator
3) Scintillation in crystal emits light photons
4) Light photons interact with photocathode and is amplified in photoamplifier tube
5) Conversion into electrical signal
2 Cardiovascular nuclear imaging tests
Heart wall motion (MUGA scan)
Myocardial perfusion and viability scan
Indication for Multigated acquition scan (MUGA) for heart wall motion
Use Tc-99m tagged RBC
- Ischemic heart disease - assess global LV function, regional wall motion and prognosis
- Non-ischemic cardiomyopathy = assess LV function
- Prior and after heart transplant
- Chemo follow-up (e.g. cardiotoxic drugs)
Classify regional wall motion seen on MUGA scans?
Hypokinesia
Akinesia
Dyskinesia
Myocardial perfusion and viability scan.
- Indications?
- Radionucleotides
Coronary artery disease**
- Myocardial infarction
- Myocardial viability, perfusion under exercise or drug stress
- Cardiac wall motion
- Treatment of CAD
- Preoperative risk assessment for sever myocardial ischemia or infarction
Thallium 201, Tc99m Sestamibi**
Describe one stress test for myocardial perfusion and viability scan
List 4 drugs for cardiac stress
Which one to use for asthma
Vasodilation by Adenosine»_space; dilate coronary vessels, stenotic vessels show ‘cold spots’
a2- agonist:
- Dipyridamole
- Adenosine
- Regadenoson
B2 agoinst (for asthma) - Dobutamine
Clinical indications for thyroid radionucleotide scan
- D/dx Hyperthyroidism
- Thyroid cancer
- Thyroid nodules
- Ectopic thyroid
- Congenital hypothyroidism
- Developmental defect: Lingual thyroid, Hemi-agenesis
Compare treatment for Thyroiditis, Grave’s, Solitary toxic nodule and Toxic multinodular goiter
Thyroiditis: Beta-blocker, steroid
Grave’s: Antithyroid drugs, surgery, 5-15mCi I-131
Solitary toxic nodule: Surgery, 15-30mCi I-131
Toxic multinodular goiter = surgery, 60mCi I-131
Thyroid CA metastasis. Type of radionucleotide scan needed?
Whole body I-131 scan
3 primary causes of hyperparathyroidism?
Secondary cases?
Primary:
Solitary adenoma
Multiglandular parathyroid disease
Parathyroid carcinoma
Secondary to chronic renal failure, GI malabsorption, rickets, drugs
Secondary to hypocalcemia > parathyroid hyperplasia
Parathyroid localization
- 3 non-invasive methods
- 4 invasive methods
Non-invasive
- US (neck)
- CT/MRI (mediastinum)
- Scintigraphy: planar, pinhole, SPECT/ SPECT-CT
Invasive:
- Image-guided biopsy/ aspiration
- Parathyroid angiography
- Parathyroid venous sampling
- Intra-operative US
Radionucleotide for parathyroid scan?
Mechanism?
Tc-99m Sestamibi (same and Myocardial perfusion scan)
Retained by Oxyphil cells (mitochondria-rich)
Early phase: traces taken up by thyroid and parathyroid
Delayed phase: Tracer washout from thyroid and leave parathyroid stain
Indication for respiratory radionucleotide scans?
2 radionucleotides?
Acute pulmonary embolism/ Chronic PE
Compares ventilation and perfusion
Perfusion = Tc-99m MAA (Macroaggregated albumin) Ventilation = Technegas
CT Angiography or VQ scan.
Advantages and disadvantages?
CT angiography:
- Faster, better resolution
- Acute PE, no need for patient cooperation
C/O pregnant, CA breast, Renal failure
VQ scan:
- Lower radiation exposure
- Safe for pregnant, young women
- High sensitivity, comparable to CTA
3 radionucleotide scans for the GI tract
- In-vitro RBC labelling (UltraTag) for GI bleeding
- Tc-99m RBC scintigraphy for fresh melena
- Merkel’s scan and scintigraphy
3 advantages of In-vitro RBC labelling (UltraTag) for GI bleeding over angiography
- Can detect lower bleed rate/ insidious bleeding
- Can detect intermittent bleeding up to 24 hours
- Less invasive
Merkel’s scan
Indication?
Mechanism?
Patient preparation?
Children with lower GI bleeding
Tc-99m Pertechnetate is secreted by tubular glands of gastric mucosa
Prep: give H2 blocker to enhance Tc-99m Per technetate uptake and inhibit gastric mucosa release before scan
Name of radionucleotide scan to evaluate biliary tree?
Indications?
EHIDA scan
- Evaluate congenital abnormalities of biliary tree: biliary atresia, choledochal cyst…etc
- Acute and chronic cholecystitis
- Detect bile leak
- Evaluate gallbladder function
Name of radionucleotide for EHIDA scan?
Mechanism?
Iminodiacetic acid (IDA)
Tc-99m IDA complex - Mebrofenin, Disofenin
IDA bound to albumin, extracted by hepatocyte, release into bile canaliculi
Structurally similar to bilirubin,. but no conjugation
Neonate with persistent cholestatic jaundice with conjugated bilirubin 10x.
Cannot see gallbladder and bile ducts after 24h of EHIDA scan
Dx?
Biliary atresia
Patient prep for EHIDA scan
Phenobarbitone for 5 days
> induce hepatic enzymes and increase secretion
Indication for radionucleotide scan of MSS?
- Bone metastasis
- Primary bone tumor assessment
- Dx Osteomyelitis
- Unexplained bone pain
- Assess metabolic bone diseases
Describe structure and adsorption of radionucleotides used for bone scans
Tc-99m Phosphate analogs: Methylene Diphosphonate
Structural analog to calcium and hydroxyl group of phosphates
Adsorbed into bone surface, affected by osteoblast activity, Vascularity and sympathetic nerve supply
Indication for Superscan (Beautiful Bone Scan)?
CA breast, CA prostate metastasis
Paget’s bone disease (localized to pelvis)
Benign:
- Renal osteodystrophy
- Secondary hyperparathyroidism
- Osteomalacia
Indication for radionucleotide scan of Genito-urinary system?
Kidney:
- Cortical imaging
- Outflow obstruction
- Transplant
- Vascular hypertension
- Vesicoureteric reflux
3 radiopharmaceuticals for genito-urinary scans?
What do they assess?
DMSA - Renal cortical binding
MAG3 - Tubular secretion
DTPA - Glomerular filtration
Pyelonephritis, renal scarring, renal infarct: which type of radionucleotide scan?
DMSA - Renal cortical binding
Describe GA-67 radionucleotide scan used for infection assessment.
Binding?
GA-67 citrate
similar to ferric ion
- Bind to lactoferrin in lymphocytes and polymorphs
- Bind to siderophores in Bacteria
- Bind to transferrin and transferrin receptor CD71 > leak through vascular epithelium at site of infection
Clinical indications for GA-67 citrate scan
Osteomyelitis
Pulmonary infection
Tuberculosis
Fever of unknown origin
Fever in immunocompromised
Autoimmune disorder
Drug induced pulmon1ary toxicity
Normal distribution of GA-67 citrate in body? (what organs uptake)
Glandular tissue: breast, lacrimal, salivary…etc
Liver, GIT, Spleen
Bone marrow, soft tissue
Thymus in children
Osteomyelitis is shown on GA-67 citrate scan. Next scan for assessment?
3 phase bone scan - assess lesion vascularity
1 - Dynamic flow study
2 - Blood pool image
3- Delayed static image
List 2 radionucleotide scans for infections
GA-67 citrate scan
White blood cell scan (IN-111 Oxine)
Describe the White blood cell scan (In-111 Oxine) for infections
Indium-111 oxine
- Lipophilic, diffuses through leukocyte membrane, oxine diffuses out of cell and Indium stays in cytoplaslm
t1/2 = 67h
Normal distribution of In-111 Oxine?
Liver
Spleen
Bone marrow
2 radionucleotide scans for brain imaging?
Purpose of these tests?
Tc-99m HMPAO (Exametaxine)
Tc-99m ECD (Bicisate)
Cognitive impairment - scan whilst questioning with MMSE
Epilepsy
Brain death
What must be excluded before Dx of brain death by radionucleotide imaging?
Exclude causes of coma
- Primary hypothermia
- Hypoglycemia
- Electrolyte imbalance
- Barbiturate overdose
- Alcohol overdose
- Sedative overdose
Pheochromocytoma, Neuroblastoma, Decarboxylation cell line tumors (paraganglioma, medullary thyroid tumor)
Which radionucleotide test to use?
MIBG scan
MetaIdodoBenzylGaunidine
Analog of Norepinephrine
Normal distribution of MIBG?
Liver Spleen Myocardium Salivary glands Adrenals Thyroid
Others: nasal mucosa, bladder, colon
Etiologies of pheochromocytoma.
Radionucleotide scan?
Sporadic 90%
Familial 10%
- MEN IIa and IIb
- Von Hippel Lindau syndrome
- Neurofibromatosis type 1
- Familial paraganglioma syndrome
MIBG scan
Radionucleotides used for breast cancer lymphatic spread?
Difference between the types?
Tc-99m sulphur colloid/ nanocolloid/ antimony trisulfide
Difference in particle size:
Large particles = slower clearance from interstitial space and slower accumulation in sentinel LN
Small particles = easily enter lymphatic capillary and enter second tier nodes
Radionucleotide for embolization?
Indication?
MoA?
Yttrium-90 glass or resin microspheres (TARE)
Palliative treatment for HCC and liver metastasis
Travel through arteries, deposit in tumor plexus/ periphery for embolization
PET principle
PET radioisotope decays and emits positron and annihilates a nearby electron
> > cause emission of 2 gamma rays travelling in opposite directions
Name one radiotracer used to scan for tumor on PET-CT
MoA
F-18 FDG
Competes with GLUT-1 receptor on cell membrane, GLUT-1 highly expressed on cancer cells
Limitation of PET- CT using radiotracers to assess tumor activity?
TB can mimic malignancy
Use of PET-MRI
Limitations
Head and neck cancer
Prostate cancer
Breast imaging
Paediatric cancers
Longer scan duration than PET-CT
No implants or pacemaker with ferrous metals
Compare PET-CT with PET- MRI
- Soft tissue contrast
- Radiation exposure
- Soft tissue contrast
PET-MRI is better - Radiation exposure
PET-CT is lower
Compare PET-CT with PET- MRI
- Attenuation correction
- Attenuation correction
PET-CT is validated
PET-MRI is not validated
Compare PET-CT with PET- MRI
- Functional or Anatomical information
- Time for scan
- Functional or Anatomical information
PET- CT = Anatomical/ morphological information
PET-MRI = functional information - Time for scan
PET-CT is much faster
