Chapter 17 Physics of Nuclear Medicine. (Radioisotopes in Medicine)

Transcription

1 (Radioisoopes in Medicine) Naural radioaciviy (Table 17.1) Becquerel (1905 Novel Prize) Curie: radium Alpha ray Nuclei of helium aoms A few cenimeers in air Posiively charges Fixed energy Bea ray or negaron (β-) High-speed elecrons A few meers in air Negaively charged Spread of energies Gamma ray Very peneraing Physically idenical o x-ray bu much higher energy Fixed energy Isoopes: single radioacive elemen Nuclei of a given elemen wih differen numbers of neurons Sable isoopes: no radioacive, 12 C, 13 C Radioisoopes: radioacive, 11 C, 14 C, 15 C Radionuclide: several radioacive elemens 1. Review of Basic Characerisics and Unis of Radioaciviy Radioacive elemen daugher (radioacive) daugher final daugher (Table 17.2) Radionuclide (Table 17.3) > KHU, EI 468

2 Mos of hem are man-made Characerisics: radioaciviy, ype and energy of is emied paricles of rays Bea-emiing radionuclide: 3 H, 14 C, 32 P are used in medicine Gamma rays: usually > 100 kev Posiron (β+): posiive bea ray, only from man-made radionuclide, physically idenical o elecron wih posiive charge Decay A = Ae λ o (A is in disinegraions/s, A o : iniial aciviy, λ: decay consan) A = λn (N is he number of radioacive aoms) Half-life, T 1/2 = : Fig λ Average or mean life ime, τ = 1.44T1/2 Uni of radioaciviy (Table 17.4) 1 curie (Ci) = disinegraions/s SI uni: Becquerel (Bq), 1 Bq = 1 disinegraions/s 2. Sources of Radioaciviy for Nuclear Medicine Radioacive drugs or radiopharmaceuical Long-lived: may be delivered from a facory Shor-lived: produced by radiopharmacis in local medical ceners Need calibraion before use 3. Saisical Aspecs of Nuclear Medicine Couning he number of gamma rays deeced from a paien in 1 min: Fig Ne coun, N ne = N g N b and N g = gross coun wih radioacive source N b = background coun wihou radioacive source (noise) Sandard deviaion of ne coun, σ ne = N g + N b KHU, EI 468

3 Nne Ne coun rae, min N = g b and sandard deviaion of ne coun rae, g N b σ = σ + σ 2 2 ne g b 4. Basic Insrumenaion and Is Clinical Applicaions Types of couning Amoun of radioaciviy in a given sample or volume Disribuion of radioaciviy in he body (imaging) Deecor Scinillaion couner: alpha paricle crysal of zinc sulfide flash or scinillaion Geiger-Mueller couner (Geiger couner or GM couner): Fig Bea ray ionizaion elecric pulse No informaion abou he amoun of ionizaion No efficien for gamma ray Phoomuliplier ube (PMT): Fig and 17.8 Scinillaion deecor Gamma ray crysal ligh phoon elecron from phoocahode more elecrons and acceleraion hrough dynodes anode Usually 10 dynodes 10 5 ~ 10 6 imes elecron muliplicaion High volage source of 1000 V Scinillaion crysal (NaI): gamma ray ligh flash (phoon) Collimaor Pulse heigh analyzer (PHA) deermines he energy of gamma ray: Fig Mulichannel analyzer (MCA): Fig Solid-sae semiconducor deecor: Fig Gamma ray elecron-hone pair generaion Collimaor: lead shield wih one or more holes: Fig Open or fla field collimaor: gamma rays from large volume (hyroid or kidney) Focused collimaor: gamma rays from small volume (imaging) KHU, EI 468

4 Applicaions 24-h upake of radioacive iodine by he hyroid: hyroid uses iodine in he producion of hormones (Fig ) Kidney funcion evaluaion using 131 I-labeled hippuric acid: hippuric acid is removed from blood by he kidney (Fig and 15) In-viro couning: well couner (Fig ) 5. Nuclear Medicine Imaging Devices Disribuion of radioaciviy image Recilinear scanner Gamma camera Recilinear scanner (Fig ) Focused collimaor Two deecors for scanning boh sides of a paien simulaneously (Fig ) Long scan ime moion arifac Gamma camera or Anger camera (Fig and 21) Large scinillaion crysal many PMTs image (Fig ) Resoluion of 5 mm Shorer imaging ime of 1 ~ 2 min Posiron camera (Fig ) 6. Physical Principles of Nuclear Medicine Imaging Procedures Cancerous nodules in he hyroid (Fig ) Liver scan (Fig ) Normal liver: filer radioacive paricles from blood Tumor in he liver: no filraion of radioacive paricle Brain umor (Fig ) Brain umor akes up some radioacive maerials beer Bone scan (Fig ) Desroyed bone due o cancer ake up more radioacive maerials o rebuild bone Pulmonary embolism (blood clo blocking a major arery in he lung) KHU, EI 468

5 Radioacive maerial in blood o deec blockage Air circulaion sysem in he lung using radioacive gas Hear scan using radioacive maerial ha will be concenraed in infarc region 7. Therapy wih Radioaciviy Radioacive drugs See Chaper Radiaion Doses in Nuclear Medicine Criical organ: an organ receiving he larges dose (Table 17.6) Gonad dose o esimae he possible generic effec of he procedure KHU, EI 468