Radiopharmaceuticals


Radiopharmaceuticals consist of a radioactive isotope, which creates the image, and a pharmaceutical, which determines the physiological behaviour of the compound and, therefore, where the signal accumulates to form the image.

 

Radiopharmaceutical

 

There are several properties of the ideal radioisotope for diagnostic purposes (i.e. not therapeutic):

  • Half life which is short enough to limit radiation dose to patient but long enough to allow good signal during imaging (ideally 1.5 x length of imaging)
  • Emits gamma rays which are of high enough energy to leave the body, reach the camera and contribute to the image. The low energy of alpha or beta particles means they are absorbed by the body which increases the radiation dose to the patient and limits the radiation that reaches the camera to produce the image
  • Mono-energetic gamma emitter (i.e. gamma rays of one energy). The ideal energy range is 100 to 250 keV for optimal imaging
  • Decays to stable daughter isotopes that will not cause significant radiation dose to patient
  • Easy to bind to different pharmaceuticals
  • Doesn't change behaviour of pharmaceutical

And 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 in order to give accurate depiction of patient's physiology

Clinical radiopharmaceuticals

There are many combinations of radioisotopes and pharmaceuticals that are used in medicine and in imaging. Some of these will produce an image and other will just produce a measurement but no image.

Classification by system

The most common imaging tests for different systems have been outlined below. 

Cardiac imaging

  • Thallium-201: For myocardial perfusion. Injected while the patient is in peak exercise or shortly after the pharmacological stress agent (adenosine) is administered. Patient is imaged immediately to see muscle that is non-perfused and then 3-4 hours later to see muscle that is persistently non-perfused i.e. irreversible infarct vs. poorly perfused i.e. ischaemia.
  • Technetium-99m (99mTc) sestamibi or tetrofosmin: For myocardial perfusion. This has a shorter half-life than thallium-201. It also requires a second injection on the delayed study.
  • MUGA: For ventriculography. The patient's RBCs are radiolabelled and injected. This study is used to assess regional and global wall motion, ventricular function and cardiac chamber size but not myocardial perfusion.

Endocrine imaging

  • 99mTc-pertechnetate: For thyroid function. Patient is imaged within 15-30 minutes after injection. 
  • 99mTc-sestamibi or tetrofosmin: for parathyroid function. Patient scanned at 20 minutes and 2 hours after injection.
  • Iodine-131 MIBG: For neuroendocrine imaging. Thyroid blockade administered 5 days before scan. Patient imaged 1-2 days after injection of I131-MIBG.
  • 99mTc-MDP (methylene diphosphonate): For bone scan. Imaged 2-5 hours after injection. Can be performed as SPECT.

Renal imaging

  • DTPA: For GFR estimation. Dynamic images acquired for 25-30 minutes after injection. Can give diuretics.
  • DMSA: For cortical function e.g. scarring. Patient imaged 3 hours after injection. Static study, not functional.

CNS imaging

  • Brain SPECT with technetium-99m HMPOA: Start imaging patient 20 minutes to 2-3 hours after injection.
  • Iodine 123 Ioflupane (aka DaTscan): SPECT. Used in imaging Parkinson's disease. Thyroid blockade administered. Patient imaged 3-6 hours after injection.

Lung imaging

  • 99mTc-DTPA aerosol: For ventilation. Static image immediately after inhalation.
  • 99mTc-MAA injection: For perfusion. Imaged immediately after injection then static images taken from different angles.

Infection / inflammation imaging

  • Gallium-67 citrate: Performed for regional or whole body imaging, planar or SPECT. Patient imaged at 48 hours and 72 hours.

Oncology imaging

  • Gallium-67 citrate: For NHL, melanoma and hepatocellular carcinoma. Image on day 2 and 3.
  • 99mTc-octreotide: imaged at 2-4 hours and at 4 hours
  • 18F-FDG PET: Imaged at 30-60 minutes after injection for 5-60 minutes.

GI imaging

  • 99mTc-mebrofenin: For hepatobiliary function. Continuous dynamic imaging up to 60 minutes. Delayed imaging at 3-4 hours if needed.
  • Radiolabeled test meal: For gastric emptying. Planar images taken 1 minute immediately after then repeated for 1 minute every hour.

Classification by radioisotope

Below is a summary of each radioisotope and the common uses. In the radioisotope header is the radioisotope, type of radiation emitted, method of production and half-life. For each radiopharmaceutical is the method of administration, whether it is used in vivo or in vitro, clinical use and whether it produces images or not. Despite the length of this table it is not exhaustive!

Carbon-11 Positron  Cyclotron 20.3 m  
C11-Choline IV In vivo PET: suspected prostate recurrence Imaging
C11-L-Methyl-methionine IV In vivo

Brain tumour imaging

Parathyroid imaging

Imaging
Carbon-14 Beta  Reactor 5730 y  
C14-Glycocholic acid Oral In vitro Breath test for small intestine bacterial overgrowth Non-imaging
C14-Urea Oral In vitro Breath test for H. pylori Non-imaging
Chromium-51 Gamma  Reactor 28 d  
Cr51 IV In vitro RBC volume heart scan, RBC sequestration, GI blood loss Non-imaging
Cr51-EDTA IV In vitro GFR Non-imaging
Cobalt-57 Gamma  Cyclotron 279 d  
Co57-Cyanocobalamin Oral In vitro GI absorption Non-imaging
Fluorine-18 Positron  Cyclotron 109 m  
F18-FDG IV In vivo

Tumour imaging

Myocardial imaging

Imaging
F18-Sodium fluoride IV In vivo bone imaging Imaging
F18-Fluorocholine IV In vivo Prostate cancer Imaging
F18-Desmothoxyfallypride IV In vivo Dopamine receptor imaging Imaging
Gallium-67 Gamma  Cyclotron 78.3 h  
Ga67-Ga3+ IV In vivo

Tumour imaging

Infection / inflammation

Imaging
Ga67-Citrate IV In vivo

Hodgkin's disease, lymphoma, bronchogenic carcinoma

Acute inflammation

Imaging
Gallium-68 Positron Generator 68 m  
Ga68-Dotatoc IV In vivo Neuroendocrine tumour Imaging
Ga68-PSMA IV In vivo Prostate cancer Imaging
Indium-111 Gamma Cyclotron 1.81 d  
In111-DTPA Intraperitoneal In vivo Ventriculoperitoneal shunt patency Imaging
In111-DTPA Intra-cisternal In vivo Cisternography Imaging
In111-leucocytes IV In vivo Infection / inflammation Imaging
In111-platelets IV In vivo Thrombus imaging Imaging
In111-Pentetreotide or Octreotide IV In vivo Neuroendocrine tumour Imaging
Iodine-123 Gamma Cyclotron 13.2 h  
I123-Iodide IV or oral In vivo

Thyroid function

Thyroid cancer metastases

Imaging
I123-MIBG IV  In vivo Neuroectodermal tumour imaging Imaging
I123-ioflupane aka DaTscan IV In vivo SPECT: Parkinson's disease Imaging
Iodine-131 Gamma and beta Reactor 8.06 d  
I131-Iodide Oral In vivo Hyperthyroidism / thyroid cancer treatment Therapeutic
I131-Iodide IV or oral In vivo Thyroid metastases Imaging
I131-MIBG IV In vivo Neuroectodermal tumour imaging Imaging
Krypton-81m Gamma Cyclotron 13 s  
K81m-gas Inhalation In vivo Lung ventilation imaging Imaging
Kr81m-aqueous solution IV In vivo Lung perfusion imaging Imaging
Oxygen-15 Positron Cyclotron 2.04 s  
O15-water IV bolus In vivo

Cerebral blood flow

Myocardial blood flow

Imaging
Strontium-89 Beta Reactor 50.5 d  
Sr89-Chloride IV In vivo Bone metastases treatment Therapeutic
Technetium-99m Gamma Generator 6.02 h  
Tc99m-Pertechnetate IV In vivo

Thyroid uptake and imaging 

Stomach and salivary glands

Meckel's diverticulum

Brain imaging

Imaging
Tc99m-human albumin IV In vivo

Cardiac blood pool / peripheral vascular imaging

Lung perfusion imaging

Imaging
Tc99m-Phosphonates and phosphates IV In vivo

Bone imaging

Myocardial imaging

Imaging
Tc99m-DTPA IV In vivo

Renal imaging

Brain imaging

Imaging
Tc99m-DTPA Inhalation In vivo Lung ventilation Imaging
Tc99m-DMSA IV In vivo

Tumour imaging

Renal function

Imaging
Tc99m-Colloid IV In vivo

Bone marrow

GI bleeding

Imaging
Tc99m-Colloid Interstitial In vivo Lymph node drainage Imaging
Tc99m-Colloid Oral In vivo

Oesophageal transit and reflux

Gastric emptying

Imaging
Tc99m-HIDA IV In vivo Functional biliary system Imaging
Tc99m-denatured RBCs IV In vivo

RBC volume

Spleen imaging

Imaging
Tc99m-whole RBCs IV In vivo

GI bleeding

Cardiac blood pool

Imaging
Tc99m-MAG3 IV In vivo Renal imaging Imaging
Tc99m-HMPOA IV In vivo Cerebral blood flow Imaging
Tc99m-examatazime labelled leucocytes IV In vivo Infection / inflammation Imaging
Tc99m-Sestamibi IV In vivo

Parathyroid / thyroid

Myocardial

Imaging
Tc99m-Tetrosfosmin IV In vivo

Parathyroid

Myocardial

Imaging
Tc99m-Tilmanocept Interstitial   Lymphatic mapping with handheld gamma counter Non-imaging
Thallium-201 Gamma Cyclotron 73.5 h  
Tl201-Tl+ IV In vivo

Thyroid tumour / parathyroid adenoma

Myocardial

Imaging
Xenon-133 Gamma Reactor 2.26 d  
Xe133-gas Inhalation In vivo Lung ventilation Imaging
Xe133 in isotonic sodium chloride solution IV In vivo Cerebral blood flow Imaging

 

 

 

Download now on Kindle
Written by radiologists, for radiologists with plenty of easy-to-follow diagrams to explain complicated concepts. An excellent resource for radiology physics revision.

 

FRCR Physics Notes: Revision notes for the First FRCR Physics exam

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