Itroduction to the Nuclear Medicine: biophysics and basic principles Zámbó Katalin Department of Nuclear Medicine
NUCLEAR MEDICINE Application of the radioactive isotopes in the diagnostics and in the therapy.
Radioactivity It is the spontaneous disintegration (decay) of the nucleus of a radioactive atom, while the element becomes to an other one.
The hydrogen atom
Number of protons = atomic number Number of protons and neutrons = mass number - Atoms with the same number of protons but differing number of neutrons are called isotopes of that element. - The behaviour of the different radioactive isotopes of an element is the same as the stable form in every conditions.
Radioactive isotopes Only certain combinations of protons and neutrons are stable, the other ones are radioactive, which become stable form by different radioactive radiations.
Activity of a radioactive atom is usually given in disintegrations per second or minute, this is the dps or dpm. The unit of the activity - 1 Bq = 1 disintegration/second - 1 kbq = 10 3 disintegration/second - 1 MBq = 10 6 disintegration/second (used in practice) Measurement - counts/second (cps) or counts/minute (cpm)
Half-life is defined as the time required for one-half of the atoms in a group of radioactive atoms to decay. - Physical half-life is characteristic for an element, independent on the external conditions. - Biological half-life depends on the physiological conditions (e.g. increased fluid input). - Effective half-life: 1/T eff = 1/T phys + 1/T biol Energy of the decay is a constant value. - Measurment unit: ev or kev or MeV 1 ev is an extremly small energy!
Types of radiation Corpuscular rays (, -, + ) Electromagnetic ray ( ) Lead Paper Penetration
Alpha radiation the emission of a helium nucleus (2 protons + 2 neutrons) the ionizating property and biological effectivity is great range in tissue is with in a few micrometers cannot be detected outside! e.g. 223 Radium for therapy of bone metastases in prostatic cancer
alpha particulum
Beta radiation - the emission of high-speed electrons - the biological effectivity is smaller than the alpha radiation - the range in tissue is a few millimeters - external detection is impossible - the biological damage to tissues is high - e.g. 131 Iodine for thyroid ablation
beta particle
Alpha particulums in bone metastasis therapy: the very short penetration in the bone decreases the exposure of the bone marrow 1,2 α-particles (short: 2-10 cells diameter) β-particles (longer: 10-1000 cells diameter) Radium Ra 223 dichlorid Bone marrow Bone Bone marrow Bone α β 1. Henriksen G, et al. Cancer Res. 2002;62:3120-3125. 2. Bruland Ø, et al. Clin Cancer Res. 2006;12:6250s-6257s. 3. Brechbiel M. Dalton Trans. 2007;43:4918-4928.
+Beta (positron) radiation too many protons are in the nucleus its life is very short, when it slows down, it combines with a normal electron in a process known annihilation, which destroyes both the electron and positron and produces two energetic photons each with 511 kev they are used for PET examinations e.g. 18-Fluor for glucose metabolic study
Gamma radiation - really electromagnetic radiation - phisically similar to X-rays, but it comes from the nucleus of the atom - very penetrated and easily pass trough tissue - SO: it can be detected externally well! - e.g. 99mTechnetium for the diagnosis
gamma photon
Mo-Tc generator - metastable state During the - and -decay the new atom remains in excited state, and it will reset with emission of -radiation. 99mTc ( -radiating, half time is 6 hours, energy is 140 KeV - ideal one for diagnostics)
Isotope Energy (kev) Tc-99m 141 6.03 h Half time Study Preparation brain, thyroid, heart, lung, liver, bone, kidney, etc. generator Tl-201 68-80 73.1 h myocardium cyclotron I-131 364 8 days thyroid dg + therapy reactor I-123 159 13 h thyroid cyclotron Ga- 67 93, 185, 300 78.1 h In-111 172 2.81 days tumor-searching, inflammation tumor-searching, immunoscintigraphy cyclotron cyclotron F-18 511 (2x) 109 min PET cyclotron
The scintillation detector
The equipments I. Gamma-camera: the present - it sees the whole entire area below the detector
Gamma-camera for the detection Display printing
SPECT (Single Photon Emission Computer Tomograph) The equipments II. SPECT/CT (Multimodality equipment) - the computer program reconstruates the transversal, sagittal and coronal slices of the organ + fusion imaging
The principle of the SPECT Patient The detectors whirl around the patient and make pictures from different steps. The reconstruction and/or the reorientation are made by the computer program from this pictures after the imaging. Transversal, sagittal and coronal slices are reconstruated and evaluated.
SPECT + CT fusion (from 2007) CT SPECT Fusion CT SPECT SPECT/CT
Equipments III. PET/CT (Positron Emission Tomograph/Computer tomograph)
The principle of the PET I. - the administered isotope is positron emitting - the annihilation 511 kev gamma-rays are detected - isotopes with ultrashort half-life ( 11 C, 15 O, 13 N, 18 F) - the metabolic changes of the heart, the brain and the tumours can be examinated
The principle of the PET II. Annihilation photons from patient Printing Ring detectors
PET + CT fusion (from 2000) CT PET
Radiation exposure - principle of ALARA (as low as reasonable achieveble) both the patients and the staff - correct indication of the examinations! - examination of pregnant women is contraindicated - children should be examined carefully
Imaging tehniques Anatomy Physiology Metabolism Molecular Rtg. / CT NM / SPECT / PET MRI MR spectroscopy fmri Ultrasound Hybrid imaging: SPECT/CT, PET/CT, (PET/MRI)
The short history of nuclear medicine - Discovery of radioactivity (Bequerel 1896) - Using of radioactive material as a tracer (György Hevesy 1943) - Development of arteficial radioactivity (Irene Curie és Frederic Joliot Curie 1934) - Gamma-camera (Anger 1951)
Radionuclide studies - are based on the function of an organ or an organ system - are very sensitive, but aspecific methods - specific for the organs (gamma-emitting isotope + carrier molecule) - are easily performed - need no any premedication - are not associated with any morbidity and complications, have only minimal risk
Method - gamma emitting isotopes, which are detected outside - carrier molecules, which paricipate in the examined function of the organs - together: radiopharmaceutical - they are usually administered intravenously in steril physiological NaCl solution - various delayed times before the examinations - imaging by scintillation detector
Static examinations (scintigraphies) - the radiopharmaceutical distribution is examined in an organ, after an optimal waiting time, from different directions, either by SPECT or SPECT/CT (morphology) Dynamic studies - a frame-serie is stored in the computer from the time of the isotope injection during an optimal time interval of the examined organ function
The blood-pool of the body Pharmaceutical Isotope Dose Studied organ Name of study Labeled RBCs Tc-99m 600 MBq blood-pool of heart ECG gated radionuclide ventriculography Labeled RBCs Tc-99m 600 MBq blood-pool of liver liver blood-pool scintigraphy
Perfusion of the organs Pharmaceutical macroalbumon thallium-clorid metoxiisobutylisonitryl (MIBI), tetrofosmin hexamethylenpropylenamin-oxym (HM-PAO) Isotope Dose Studied organ Name of study Tc-99m 15-200 MBq lung perfusion lung scintigraphy Tl-201 Tc-99m 74 MBq 600 MBq myocardium perfusion Tc-99m 800 MBq brain perfusion rest and stress mycardial perfusion study brain perfusion study diethylentriaminpentaacetate (DTPA) Tc-99m 600 MBq heart, bone, kidney, etc. perfusion dinamyc perfusion studies
Radiopharmaceuticals in parenchymal cells Pharmaceutical Isotope Dose Studied organ Name of study pertechnetate Tc-99m 37-74 MBq thyroid thyroid scintigraphy colloids Tc-99m 150-200 MBq iminodiacetate (HIDA) dimercaptosuccinylamid (DMSA) diethylentriaminpentaacetate (DTPA) mercaptoacethyltriglicyl (MAG3) liver, spleen RES cells Tc-99m 150-200 MBq liver hepatocytes liver, spleen scintigraphy hepatobiliar scintighraphy Tc-99m 150-200 MBq renal tubular cells renal scintigraphy Tc-99m 400 MBq 200 MBq renal glomerular cells renal tubular cells renal perfusion and renography
Radiopharmaceuticals in tumor cells Pharma-ceutical Isotope Dose Studied organ Name of study NaI I-131 74 MBq (dg) 1000-3700 MBq (th) diphosphonates Tc-99m 800 MBq metoxi-isobutylisonitryl (MIBI) tetrofosmin thallium-clorid meta-iodo-benzylguanidine (MIBG) methylnorcholesterol octreotide depreotide human serum albumin (HSA)- nanocolloid fluoro-dezoxyglucose (FDG) Tc-99m Tl-201 I-131 I-123 600 MBq 74 MBq 40 MBq 185 MBq differentiated thyroid cancer bone tumors and metastases parathyroid adenomas breast tumor, etc. neuroblastoma, pheocromocytoma thyroid scintigraphy + therapy bone scintigraphy tumor, metastasis searching adrenerg receptor study I-131 40 MBq adrenal gland cortex hormon-syntesis study In-111 Tc-99m 122 MBq 800 MBq carcinoid, GEP tumors, lung tumors somatostatin receptor study Tc-99m 20-60 MBq sentinel lymph node limfoscintigraphy F-18 6 MBq/kg (111-555 MBq) different tumors glucose metabolism PET study