Radioisotope imaging uses radioactive tracers and gamma cameras to produce images of physiological processes. Technetium-99m is commonly used due to its short half-life and gamma ray emissions. Common scans include thyroid scans using iodine-123 or technetium, parathyroid scans using sestamibi, MIBG scans for pheochromocytoma, bone scans, renal scans using DTPA or MAG3, and HIDA scans of the gallbladder. PET scans using fluorodeoxyglucose provide functional imaging combined with anatomical data from CT scans and are useful for cancer staging, treatment response, and detecting recurrence.

1. Radioisotope Imaging
A Bharath
Final year PG

2. • Introduction
• Historical perspective
• Components in Imaging
• Uses in surgical field
• PET and Hybrid imaging

3. Introduction
• Nuclear medicine is a medical specialty involving the application of
radioactive substances in the diagnosis and treatment of disease.
• Nuclear imaging is a form of physiologic imaging.
• Produces images of physiologic processes utilizing radioactive
isotopes

4. History
• In mid 1920s George de Hevesy made experiments with radionuclides
administered to rats
• Discovery of artificially produced radionuclides by Frédéric Joliot-Curie
and Irène Joliot-Curie in 1934
• In 1936, John Lawrence, known as "the father of nuclear medicine",
his brother Ernest Lawrence made the first application in patients of
an artificial radionuclide - Phosphorus-32 to treat leukemia.

5. • December 7, 1946 - article was published in the Journal of the
American Medical Association by Sam Seidlin - successful treatment
of a patient with thyroid cancer metastases using I-131
• Technetium-99m was first discovered in 1937 by C. Perrier and E.
Segre, is the most utilized element in nuclear medicine and is
employed in a wide variety of nuclear medicine imaging studies.

6. Components of imaging
• Radionucleide
•eg: Tc99m, I 123, I 131
• Radiopharmaceutical / Tracer
•pertechnate, sestamibi, NaI
• Gamma camera

7. Radionucleide / Radioisotope
There are several properties of the ideal radioisotope for diagnostic
purposes:
•Half life - short enough to limit radiation dose, but long enough to
allow good signal during imaging (ideally 1.5 x length of imaging)
•Emits only gamma rays
•Mono-energetic - ideal energy range is 100 to 250 keV
•Decays to stable daughter isotopes
•Easy to bind to different pharmaceuticals

8. Technetium 99m
• First artificial element to be produced
• Generated from Mo99 in a cyclotron
• Half life - 6hrs
• Emits gamma rays 140KeV
• Used in more than 70% of nuclear medicine scans

9. Radiopharmaceutical / Tracer
There are several properties of the ideal pharmaceutical:
•High target:non-target uptake ratio
•Easy and cheap to produce
•Non-toxic
•Does not alter physiology

10. Gamma Camera
• The Gamma camera consists of a
large area NaI crystal with a lead
collimator which allows only
transmission of radiation from a
particular point.
• The detector device can be
moved to cover larger areas.

12. Types of Imaging
• Static planar scintigraphy - provides 2D representations of a three
dimensional object by measuring the spatial distribution of the
radioisotope in the body
• Dynamic planar scintigraphy - measures temporal changes in the
spatial distribution of the radioisotopes in the body by taking multiple
images

13. • Single photon emission tomography (SPECT) or positron emission
tomography (PET) which allows to form 3D static or dynamic
representations of the organ and organ functions by taking multiple
images from different directions.

14. Commonly used scans in surgical field
• Thyroid scintigraphy
• Parathyroid sestamibi scan
• MIBG scan
• Bone scan
• DTPA, DMSA, MAG3
• HIDA scan
• Labelled RBC for GI bleeding
• Meckels diverticulum

15. RAIU test
• Radioactive iodine uptake test is used to evaluate functional status of
thyroid gland or nodule
• I 123 is given in form of Sodium iodide (100-200 uCi)
• Tracer is given orally
• Images are taken 24hr later
• Normal uptake is around 25%
• Based on uptake, gland/nodule is labelled as hot or cold

16. Increased Uptake
•Hyperthyroidism
•Hashimoto’s thyroiditis
•Decreased renal clearance of
iodine
•Iodine deficiency
Decreased Uptake
•Hypothyroidism (primary or
secondary)
•TSH resistance
•Thyroid hormone replacement,
suppression
•Iodine excess (dietary, drugs)

18. • I 123 has lower half life
• Emits pure Gamma rays
• Emitted gamma rays are ideal
for imaging
• Has minimal radiation exposure
risk
• Does not cause stunning of
tissue
• Expensive
• I 131 has higher half life
• 90% is beta decay
• Gamma rays emitted are of
higher energy
• Radiation exposure is 100 times
more
• Stuns tissue that it accumulates
in
• Much cheaper than I 123

19. • Routine use of RAIU test is ill advised
• Main implication is in hyperthyroid patient with goitre
• Malignancy is sen in 20% of cold noduls and 5% of hot nodules
• Though suggestive, malignancy is neither confirmed nor excluded
using RAIU test
• Thyroid scintigraphy can also be done using Tc99m but has few
drawbacks

20. • Tc pertechnate is rapidly taken up by follicular cells
• Trapped but not organified
• Short half life helps in rapid evaluation of functioning and non
functioning areas of thyroid gland
• Taken up by other structures like salaivary glands and vascular
structures

21. Parathyroid scintigraphy
• Sestamibi is monovalent, lipophilic cation which accumulates in
mitochondria
• Initially used for myocardial perfusion
• In 1989, its affinity for abnormal parathyroid tissue was identified
• Radionucleide used is Tc99m
• Sensitivity decreases in case of simultaneous thyroid pathology

22. 3 types of imaging
•Subtraction imaging using both I 123 and Tc sestamibi
•Dual phase sestamibi scan
•Sestamibi SPECT

24. Pheochromocytoma
• Meta iodo benzyl guanine (I 123)
• Used for pre operative localization of Pheochromocytoma
• Tracer is given IV and images are taken at different time intervals
• F18 L DOPA scan is superior at identifying and localizing the tumor
• More costly and lesser availablity

25. MIBG is specifically done in patients who have
•equivocal CT/MRI
•suspected of having multifocal disease
•suspected of having malignant disease
•Highly specific for pheochromocytoma but sensitivity is only about 75-
90%
•F18 DOPA PET scans have higher sensitivity and specificity

30. Bone Scintigraphy
• Tc labelled methylene diphosphate
• Binds to hydroxyapatite crystals proportional to blood flow and
osteoblastic activity
• Hence is a marker of bone perfusion and turnover
• Mainly useful to detect bone secondaries
• Choice of radioisotope can vary depending on primary tumor

32. Renal cortex scintigraphy
• Di mercapto succinic acid
• Labelled with Tc99m
• Accumulates in Proximal tubular cells of renal cortex
• Static scan
• Position, size and morphology of renal cortex can be evaluated
• Any loss of renal cortex can be noted - renal scarring
• Pitfalls - UTI, HUN

35. Radioisotope Renogram
• Diethylene triamine penta acetate
• Mercapto acyltriglycine
• Both are Tc99m labelled
• DTPA is excreted through Glomerular filteration
• MAG3 is excrete through secretion in proximal tubules

37. Cholescintigraphy
• Hepatobiliary imido diacetic acid
• Tc99m labelled lidofenin
• Secreted into bile about 1hr after administration
• Can identify anomalies or obstructions in biliary tree
• Also used to diagnose gallbladder dysfunction
• Not the first line investigation and considered only if MRI is not
available

39. GIB scintigraphy
• Gastro intestinal bleeding scintigraphy
• initially Tc99m sulphur colloid was used
• Tc99m labelled RBC are used now
• Useful mainly in small bowel and lower gi bleeding

42. Meckels diverticulum
• 60% of diverticulae tend to have ectopic mucosa
• more than 70% have gastric mucosa
• Tc99m labelled Na pertechnate is used
• Taken up by mucin secreting cells of gastric mucosa
• Its sensitivity decreases after adolescence
• False positives can be seen with vasular malformations or other sites
of ectopic gastric mucosa

45. PET
• Positron emission tomography
• Positron emmitters are used as radionucleides
• Emitted positron travels short distance and interacts with electron
• Resulting in 2 gamma photons travelling at 180 degrees
• These are recognised by detectors and position is localised and a 3D
image is created

46. • PET scan is used in various fields but has important role in oncology
• F18 is the most commonly used isotope
• Used in form of Fluoro deoxy glucose
• Accumulated in cells that actively uptake glucose for metabolism

47. Hybrid Imaging
• PET-CT combines, in a single gantry, a PET scanner and a CT scanner,
to acquire sequential images from both devices in the same session,
which are combined into a single superposed image
• Functional imaging obtained by PET, can be more precisely correlated
with anatomic imaging obtained by CT scanning

48. Uses
• staging of carcinoma
• establish baseline staging before commencing treatment
• evaluation of an indeterminate/equivocal lesion on conventional
imaging
• assessing response to therapy
• evaluation of suspected disease recurrence or relapse
• to guide a biopsy (e.g. pleural biopsy for mesothelioma)

49. • In work up of an occult primary lesion
• differentiate between radiation-induced necrosis and tumour
recurrence

50. Take Home
• While some procedures have become obsolete owing to
developments in CT and MRI, still there are specific indications for
isotope scans
• Using in combination with CT is more informative
• Only contraindications are Pregnancy and Lactation

51. Thank You