Itroduction to the Nuclear Medicine: biophysics and basic principles. Zámbó Katalin Department of Nuclear Medicine

Transcription

1 Itroduction to the Nuclear Medicine: biophysics and basic principles Zámbó Katalin Department of Nuclear Medicine

2 NUCLEAR MEDICINE Application of the radioactive isotopes in the diagnostics and in the therapy.

3 Radioactivity It is the spontaneous disintegration (decay) of the nucleus of a radioactive atom, while the element becomes to an other one.

4 The hydrogen atom

5

6 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.

7 Radioactive isotopes Only certain combinations of protons and neutrons are stable, the other ones are radioactive, which become stable form by different radioactive radiations.

8 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)

9 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!

10 Types of radiation Corpuscular rays (, -, + ) Electromagnetic ray ( ) Lead Paper Penetration

11 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

12 alpha particulum

13 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

14 beta particle

15 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: cells diameter) Radium Ra 223 dichlorid Bone marrow Bone Bone marrow Bone α β 1. Henriksen G, et al. Cancer Res. 2002;62: Bruland Ø, et al. Clin Cancer Res. 2006;12:6250s-6257s. 3. Brechbiel M. Dalton Trans. 2007;43:

16 +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

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18 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

19 gamma photon

20 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)

21 Isotope Energy (kev) Tc-99m h Half time Study Preparation brain, thyroid, heart, lung, liver, bone, kidney, etc. generator Tl h myocardium cyclotron I days thyroid dg + therapy reactor I h thyroid cyclotron Ga , 185, h In days tumor-searching, inflammation tumor-searching, immunoscintigraphy cyclotron cyclotron F (2x) 109 min PET cyclotron

22 The scintillation detector

23 The equipments I. Gamma-camera: the present - it sees the whole entire area below the detector

24 Gamma-camera for the detection Display printing

25 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

26 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.

27 SPECT + CT fusion (from 2007) CT SPECT Fusion CT SPECT SPECT/CT

28 Equipments III. PET/CT (Positron Emission Tomograph/Computer tomograph)

29 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

30 The principle of the PET II. Annihilation photons from patient Printing Ring detectors

31 PET + CT fusion (from 2000) CT PET

32 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

33 Imaging tehniques Anatomy Physiology Metabolism Molecular Rtg. / CT NM / SPECT / PET MRI MR spectroscopy fmri Ultrasound Hybrid imaging: SPECT/CT, PET/CT, (PET/MRI)

34 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)

35 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

36 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

37 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

38 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

39 Perfusion of the organs Pharmaceutical macroalbumon thallium-clorid metoxiisobutylisonitryl (MIBI), tetrofosmin hexamethylenpropylenamin-oxym (HM-PAO) Isotope Dose Studied organ Name of study Tc-99m 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

40 Radiopharmaceuticals in parenchymal cells Pharmaceutical Isotope Dose Studied organ Name of study pertechnetate Tc-99m MBq thyroid thyroid scintigraphy colloids Tc-99m MBq iminodiacetate (HIDA) dimercaptosuccinylamid (DMSA) diethylentriaminpentaacetate (DTPA) mercaptoacethyltriglicyl (MAG3) liver, spleen RES cells Tc-99m MBq liver hepatocytes liver, spleen scintigraphy hepatobiliar scintighraphy Tc-99m MBq renal tubular cells renal scintigraphy Tc-99m 400 MBq 200 MBq renal glomerular cells renal tubular cells renal perfusion and renography

41 Radiopharmaceuticals in tumor cells Pharma-ceutical Isotope Dose Studied organ Name of study NaI I MBq (dg) 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 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 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 MBq sentinel lymph node limfoscintigraphy F-18 6 MBq/kg ( MBq) different tumors glucose metabolism PET study