Fysisk institutt - Rikshospitalet 1

2 Overview Gamma camera Positron emission technology (PET) Computer tomography (CT) Proton therapy Electrical impedance tomography (EIT)

Scintillation- detector

Gamma Camera A camera for nuclear imaging. The most used so far was invented by H. Anger in the 1960’s (The Anger camera)

Anger camera Photons with a proper direction are let through the collimator, into the detector and photomultipliers

Anger Camera (cont.)

Gamma-camera

Collimator focusing

Actual isotopes (1)

Actual isotopes (2) half life ”parents”

Line spread and MTF

PET camera

Annihilation coincidence detection Emitted positrons lose their kinetic energy by causing excitation and ionization A positron that has lost most of the energy will interact with an electron by an annihilation This annihilation will convert the mass of the electron- positron pair into two 511-keV photons, emitted in contrary directions

Annihilation coincidence detection If a simultaneous photon is registered in two different detectors, the annihilation came into being along a straight line between the two detectors. The electronics within a scanner detects the simultaneous hits in a process called annihilation coincidence detection When two simultaneous hits have been detected, a line between the two detectors is calculated

True, random, and scatter coincidences A true coincidence = detection is the result of a single nuclear annihilation A random coincidence = photons from different nuclear transformations are detected simultaneously at the detectors. May give erroneous results. A scatter coincidence = one or both photons from a single annihilation are scattered in different directions but still detected in the detector

Design of a PET scanner PET = scintillation crystals coupled to photomulitiplier tubes (PMT) The signals are then processed in pulse mode in order to find the position, energy and the timestamp for each interaction The energy levels can be used to discriminate between scatter coincidences and true coincidences Early PET scanners coupled each scintillation crystal to a single PMT –Size of individual crystal largely determined spatial resolution of the system Modern designs couple larger crystals to more than one PMT Relative magnitudes of the signals from the PMTs coupled to a single crystal used to determine the position of the interaction in the crystal

Fysisk institutt - Rikshospitalet 23 PET-CT Usually combined with CT in order to localize activity in the body

Non-invasive surgery Kilde: NIRS, Chiba, Japan

Non-invasive surgery Kilde: NIRS, Chiba, Japan Heavy ion therapy (Proton-terapi)

Non-invasive surgery A treatment for patients with a local tumor not possible to treat with regular therapeutic methods Kilde: Magne Guttormsen, Fysisk Institutt, UIO

Non-invasive surgery Better dose distribution to the tumor Source: Magne Guttormsen, Fysisk Institutt, UIO

Non-invasive surgery Kilde: NIRS, Chiba, Japan

Non-invasive surgery Kilde: NIRS, Chiba, Japan Minimalized heavy ion therapy centre Tung-kjerne terapi sentre - Less size than today’s centres - Reduced investmentcost, approximately 800 mill NOK

Computertomography (CT)

Computertomograph (CT)

What is the CT? Mathematical transform to the measured data. Reconstruct n dimension function (image) => projection data of n – 1 dimension Radon Transform (1917) “Two dimension and three dimension object can be reconstructed from the infinite set of projection data”. The First CT: 1973 in the U.S. 4 minutes scan, thickness of 10mm

Concept of CT ・ Getting the shape by back projection of the projection data. ・ For example, outward view is the quadrangle => it is the cylinder CT Algorithm

X Basic principle of CT -Reconstruction of 2 dimensional image- Simple Backprojection Projection Data Blur x y x y curvilinear integral of absorption coefficient regarding Y object X-ray tube X-ray detector array Data Acquisition field Reconstruction field X X Y

1., 2. and 3. generation scanner Linear translation + rotation Cirkular scanning Volume scanning

CT picture old technology

CT picture new technology Source:

Geometry of a CT-scanner

Image reconstruction

Back- projection (1)

Back- projection (2)

Basic principle of CT -Reconstruction of 2 dimensional image- Filtered Backprojection Projection Data x y ＊ x Multidirectional Backprojection Reconstruction Filter ω or x Filtered Projection data x X

CT image

CT 3-D image

2D og 3D images

Rapidscanner

Fysisk institutt - Rikshospitalet 47 Multislice CT Several rings of detectors for multiple scanning of several layers. Time efficiant, a 4 slice multislice CT is up to 8 times faster than a single slice CT Possible monitoring of a beating heart ++

Reconstruction process

Data acquisition at angle : 0 – 180 degree Obtain F(u,v) and then 2D IFFT -> reconstruction Radon Transform is equivalent to Filtered backprojection !

Example of Simulation Model ImageSimple Backprojection Filtered Backprojection

Electrical impedansetomography (kap 8.7)

Image buildup

EIT, praktical measurement

Fysisk institutt - Rikshospitalet 54 EIT, Example Dräger Until now, impossible to get a real time image of lung ventilation bedside without using expensive/cumbersome methods. Impedance-based new add-on to Dräger ventilators Non-invasive, no harmful influence on the patient

Nuclearmedical images