Diagnostic radiology - Nuclear Medicine

Question 1

Most common radionucleotide?

Answer 1

Technetium-99m

Question 2

Function of radionucleotide imaging?

Answer 2

Use radioactive isotopes-emitted ionizing radiation to assess organ function and structure

Detect changes in metabolism, blood flow, regional chemical composition

Question 3

Difference between Gamma radiation and X-ray

Answer 3

Gamma rays have higher energy and penetrating power than X-ray

X-ray = photons emitted from electron orbits
Gamma rays = photons emitted from nucleus

Question 4

Explain how a gamma camera works

Answer 4

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

Question 5

2 Cardiovascular nuclear imaging tests

Answer 5

Heart wall motion (MUGA scan)

Myocardial perfusion and viability scan

Question 6

Indication for Multigated acquition scan (MUGA) for heart wall motion

Answer 6

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)

Question 7

Classify regional wall motion seen on MUGA scans?

Answer 7

Hypokinesia
Akinesia
Dyskinesia

Question 8

Myocardial perfusion and viability scan.

• Indications?
• Radionucleotides

Answer 8

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**

Question 9

Describe one stress test for myocardial perfusion and viability scan

List 4 drugs for cardiac stress
Which one to use for asthma

Answer 9

Vasodilation by Adenosine&raquo_space; dilate coronary vessels, stenotic vessels show ‘cold spots’

a2- agonist:

• Dipyridamole
• Adenosine
• Regadenoson

B2 agoinst (for asthma)
- Dobutamine

Question 10

Clinical indications for thyroid radionucleotide scan

Answer 10

• D/dx Hyperthyroidism
• Thyroid cancer
• Thyroid nodules
• Ectopic thyroid
• Congenital hypothyroidism
• Developmental defect: Lingual thyroid, Hemi-agenesis

Question 11

Compare treatment for Thyroiditis, Grave’s, Solitary toxic nodule and Toxic multinodular goiter

Answer 11

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

Question 12

Thyroid CA metastasis. Type of radionucleotide scan needed?

Answer 12

Whole body I-131 scan

Question 13

3 primary causes of hyperparathyroidism?

Secondary cases?

Answer 13

Primary:
Solitary adenoma
Multiglandular parathyroid disease
Parathyroid carcinoma

Secondary to chronic renal failure, GI malabsorption, rickets, drugs

Secondary to hypocalcemia > parathyroid hyperplasia

Question 14

Parathyroid localization

• 3 non-invasive methods
• 4 invasive methods

Answer 14

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

Question 15

Radionucleotide for parathyroid scan?

Mechanism?

Answer 15

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

Question 16

Indication for respiratory radionucleotide scans?

2 radionucleotides?

Answer 16

Acute pulmonary embolism/ Chronic PE

Compares ventilation and perfusion

Perfusion = Tc-99m MAA (Macroaggregated albumin)
Ventilation = Technegas

Question 17

CT Angiography or VQ scan.

Advantages and disadvantages?

Answer 17

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

Question 18

3 radionucleotide scans for the GI tract

Answer 18

1. In-vitro RBC labelling (UltraTag) for GI bleeding
2. Tc-99m RBC scintigraphy for fresh melena
3. Merkel’s scan and scintigraphy

Question 19

3 advantages of In-vitro RBC labelling (UltraTag) for GI bleeding over angiography

Answer 19

• Can detect lower bleed rate/ insidious bleeding
• Can detect intermittent bleeding up to 24 hours
• Less invasive

Question 20

Merkel’s scan
Indication?
Mechanism?
Patient preparation?

Answer 20

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

Question 21

Name of radionucleotide scan to evaluate biliary tree?

Indications?

Answer 21

EHIDA scan

• Evaluate congenital abnormalities of biliary tree: biliary atresia, choledochal cyst…etc
• Acute and chronic cholecystitis
• Detect bile leak
• Evaluate gallbladder function

Question 22

Name of radionucleotide for EHIDA scan?

Mechanism?

Answer 22

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

Question 23

Neonate with persistent cholestatic jaundice with conjugated bilirubin 10x.
Cannot see gallbladder and bile ducts after 24h of EHIDA scan
Dx?

Answer 23

Biliary atresia

Question 24

Patient prep for EHIDA scan

Answer 24

Phenobarbitone for 5 days

> induce hepatic enzymes and increase secretion

Question 25

Indication for radionucleotide scan of MSS?

Answer 25

- Bone metastasis - Primary bone tumor assessment - Dx Osteomyelitis - Unexplained bone pain - Assess metabolic bone diseases

Question 26

Describe structure and adsorption of radionucleotides used for bone scans

Answer 26

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

Question 27

Indication for Superscan (Beautiful Bone Scan)?

Answer 27

CA breast, CA prostate metastasis Paget's bone disease (localized to pelvis) Benign: - Renal osteodystrophy - Secondary hyperparathyroidism - Osteomalacia

Question 28

Indication for radionucleotide scan of Genito-urinary system?

Answer 28

Kidney: - Cortical imaging - Outflow obstruction - Transplant - Vascular hypertension - Vesicoureteric reflux

Question 29

3 radiopharmaceuticals for genito-urinary scans? | What do they assess?

Answer 29

DMSA - Renal cortical binding MAG3 - Tubular secretion DTPA - Glomerular filtration

Question 30

Pyelonephritis, renal scarring, renal infarct: which type of radionucleotide scan?

Answer 30

DMSA - Renal cortical binding

Question 31

Describe GA-67 radionucleotide scan used for infection assessment. Binding?

Answer 31

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

Question 32

Clinical indications for GA-67 citrate scan

Answer 32

Osteomyelitis Pulmonary infection Tuberculosis Fever of unknown origin Fever in immunocompromised Autoimmune disorder Drug induced pulmon1ary toxicity

Question 33

Normal distribution of GA-67 citrate in body? (what organs uptake)

Answer 33

Glandular tissue: breast, lacrimal, salivary...etc Liver, GIT, Spleen Bone marrow, soft tissue Thymus in children

Question 34

Osteomyelitis is shown on GA-67 citrate scan. Next scan for assessment?

Answer 34

3 phase bone scan - assess lesion vascularity 1 - Dynamic flow study 2 - Blood pool image 3- Delayed static image

Question 35

List 2 radionucleotide scans for infections

Answer 35

GA-67 citrate scan | White blood cell scan (IN-111 Oxine)

Question 36

Describe the White blood cell scan (In-111 Oxine) for infections

Answer 36

Indium-111 oxine - Lipophilic, diffuses through leukocyte membrane, oxine diffuses out of cell and Indium stays in cytoplaslm t1/2 = 67h

Question 37

Normal distribution of In-111 Oxine?

Answer 37

Liver Spleen Bone marrow

Question 38

2 radionucleotide scans for brain imaging? | Purpose of these tests?

Answer 38

Tc-99m HMPAO (Exametaxine) Tc-99m ECD (Bicisate) Cognitive impairment - scan whilst questioning with MMSE Epilepsy Brain death

Question 39

What must be excluded before Dx of brain death by radionucleotide imaging?

Answer 39

Exclude causes of coma - Primary hypothermia - Hypoglycemia - Electrolyte imbalance - Barbiturate overdose - Alcohol overdose - Sedative overdose

Question 40

Pheochromocytoma, Neuroblastoma, Decarboxylation cell line tumors (paraganglioma, medullary thyroid tumor) Which radionucleotide test to use?

Answer 40

MIBG scan MetaIdodoBenzylGaunidine Analog of Norepinephrine

Question 41

Normal distribution of MIBG?

Answer 41

``` Liver Spleen Myocardium Salivary glands Adrenals Thyroid ``` Others: nasal mucosa, bladder, colon

Question 42

Etiologies of pheochromocytoma. | Radionucleotide scan?

Answer 42

Sporadic 90% Familial 10% - MEN IIa and IIb - Von Hippel Lindau syndrome - Neurofibromatosis type 1 - Familial paraganglioma syndrome MIBG scan

Question 43

Radionucleotides used for breast cancer lymphatic spread? | Difference between the types?

Answer 43

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

Question 44

Radionucleotide for embolization? Indication? MoA?

Answer 44

Yttrium-90 glass or resin microspheres (TARE) Palliative treatment for HCC and liver metastasis Travel through arteries, deposit in tumor plexus/ periphery for embolization

Question 45

PET principle

Answer 45

PET radioisotope decays and emits positron and annihilates a nearby electron >> cause emission of 2 gamma rays travelling in opposite directions

Question 46

Name one radiotracer used to scan for tumor on PET-CT | MoA

Answer 46

F-18 FDG Competes with GLUT-1 receptor on cell membrane, GLUT-1 highly expressed on cancer cells

Question 47

Limitation of PET- CT using radiotracers to assess tumor activity?

Answer 47

TB can mimic malignancy

Question 48

Use of PET-MRI Limitations

Answer 48

Head and neck cancer Prostate cancer Breast imaging Paediatric cancers Longer scan duration than PET-CT No implants or pacemaker with ferrous metals

Question 49

Compare PET-CT with PET- MRI - Soft tissue contrast - Radiation exposure

Answer 49

- Soft tissue contrast PET-MRI is better - Radiation exposure PET-CT is lower

Question 50

Compare PET-CT with PET- MRI - Attenuation correction

Answer 50

- Attenuation correction PET-CT is validated PET-MRI is not validated

Question 51

Compare PET-CT with PET- MRI - Functional or Anatomical information - Time for scan

Answer 51

- Functional or Anatomical information PET- CT = Anatomical/ morphological information PET-MRI = functional information - Time for scan PET-CT is much faster