Diagnostic imaging techniques. Krasznai Zoltán. University of Debrecen Medical and Health Science Centre Department of Biophysics and Cell Biology

Transcription

1 Diagnostic imaging techniques Krasznai Zoltán University of Debrecen Medical and Health Science Centre Department of Biophysics and Cell Biology

2 1. Computer tomography (CT) 2. Gamma camera 3. Single Photon Emission Computer Tomography (SPECT) 4. Pozitron Emission Tomography (PET)

3 Computer tomography (CT) CT is a diagnostic imaging technique that provides information about a slice perpendicular to the longitudinal axis of the examined body.

4 The a, b and c squares can not be distinguished on the base of their projection to the y axis.

5 If we take into consideration their projection to the x axis, the c square can be properly drown, but the a and b squares still look uniform.

6 Modeling the density matrix radiation source detector

7 The attenuation of the I 0 intensity of X-ray can be discribed as: I x = I 0 e -μx The I A-D intensities are the following: I A = I 0 e -(D1+D2) I B = I 0 e -(D3+D4) I C = I 0 e -(D2+D4) I D = I 0 e -(D1+D3) where D k = μx

8 Good resolution requires small voxel size! For all measured I k intensities it is determined which voxels are between the rotating radiation source and the detector. That is called back projection.

9 Following it using Furier transformation the density matrix can be reconstucted. I k = I 0 e - μl where I 0 is the X-ray intensity entering to the body, l a distance the X-ray travels in the body and μ the average attenuation coefficient for the given distance μ=( μ i Δl) /n = D i /n where n is the number of voxels on the given distance.

10 In the energy range used in CT ( kv X-ray tube voltage) The X-ray attenuates mainly by Compton effect (85%) and by fotoeffect (15%). Pair production can not occur. The attenuation in a voxel has two components: μ x = τ x + σ x where τ = absorption coefficient σ = scattering coefficient

11 Both have additional components: μ x = p ρ x Z n eff,x + s ρ x (Z/A) eff,x ρ = density Z = atomic number Z eff,x = Effectiv atomic number n = exponential power (appr. 3) s = scattering constant at a given voltage A = mass number

12 The attenuation coefficient depends upon the atomic and mass number of the material Element Z A Z 3 Z/A H C N O Ca Fe I Ba

13 The Ba and I atoms (because the 3. power of their atomic number is high) shift the attenuation to higher absorption! The contrast material selectively modify the absorption coefficients of the voxels in different tissues/organs. The most frequently applied contrast material is the iodin bound to different organic carries/metabolites. CT angiography (CTA) Renotrop and hepatotrop contrast materials. Dinamyc CT examinations.

14 The density values in CT are expressed in HOUNSFIELD (HU) units. The attenuation of the air and the water are constant (-1000 HU and 0 HU) The density values of few tissues/organs in HU units: Tissue/organ Compact bones Spongy bones Liver Kidney Plasma Lung HU value between between ± 5 30 ± ± 2 between

15 Block scheme of the different generations of CT a detector Radiation source

16 b detector radiation source

17 c detector radiation source

18 d d detector Wolfram ring elektron beam deflecting coil

19 deflecting coil elektron beam Wolfram ring

20 Possible development of CT: Faster speed of the X-ray tube Inceased number of detectors Smaller size of detectors 1 mm slices 3 dimensional secondary image reconstruction. Unravel secondary image reconstruction (so called Janus projection) (data generated from the digital image)

21 Spiral CT Dynamic Volume Scanning, DVS Using continuously moving X-ray tube and patient table in helical (spirális) arrangement within sec all voxel densities of a relatively thick slice of body cylinder can be determined. This method results in an excellent 3 dimension secondary image reconstruction which coupled with Janus projection, using contrast material makes CT angiography possible.

22 CT images of a healthy human brain and after stroke

23 Gamma-camera Using gamma camera the two dimensional projections of γ radiation of radioactive isotope labeled pharmacons from the human body can be detected.

24 Principle of gamma scintillation examinations

25 Upper view of the scintillation crystal and the connected photoelectron amplifiers

26 Renogram showing the kidneys function Counts/sec furosemid injection Right kidney Left kidney Time (min)

27 Block scheme of the scintillation gamma camera Matrix circuit Differential discriminator ADC ADC

28 Scanning trajectory following the body contour

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30 Positron Emission Tomography PET A PET is a functional imaging method, that provides information about the distribution of the radioactive isotope labeled metabolite administered into the body for diagnostic purpose.

31 Positron-electron annihilation electron/positron annihilation β β + photon γ Conservation of momentum Before: annihilation the momentum of the system is ~ 0 After:two photons of the same energy travelling to opposite directions are created photon γ decay by positron emission Conservation of energy Before: two electrons, with mass equivalent 2 x 511 kev After: two photons with 511 kev energy each

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33 Block diagram of a PETexamination Production of positron emitting isotope (ciklotron) Injection of the radiopharmacon Data collection Processing of data Synthesis of the radiopharnacon Image reconstruction Interpretation

34 Data collection

35 Data collection

36 Data collection

37 Data collection

38 Image construction

39 Image construction

40 Characteristics of the PET-method Advantages: high sensitivity high spatial resolution high selectivity characteristic for the applied radiopharmacon low radiation dose Disadvantages: low accessibility time consuming high cost

41 Commonly used radiopharmacons 18 FDG Image construction is on the base of glucose metabolism [ 11 C]-metionin Image construction is on the base of protein synthesis (helps in differentiating malignant tumours from inflammations)

42 The PET-camera in Debrecen GE

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44 Image registration: anatomically equivalent sections CT FDG-PET

45 Image fusion: overlayed visualization

46 Epipharynx-tumour & 3D fusion axial sagittal coronal

47 Image fusion based 3D radiotherapy planning

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53 Whole body 3D fusion

54 The main metabolic differences between normal tissue and cancer increased glycolysis (FDG uptake) increased protein synthesis (C11methionine uptake) increased amino acid transport (C11methionine uptake) increased or decreased receptor densities (radionuclid labeled ligands show receptor densities) increased DNA synthesis (C11 thymidine uptake) increased blood flow (O15 butanol/or water uptake) more anoxic and hypoxic cells (F18 labeled ligand uptake)

55 Low-grade astrocytoma FDG METHIONINE

56 Low-grade recurrent glioma (FDG)

57 Low-grade recurrent glioma (MET)

58 Recurrent colorectal cc. & metastases

59 Malignant melanoma Before chemotherapy After chemotherapy

60 Search for unknown tumour No. 1 Metastatic lymph node on the right side of the neck CT [ 11 C]Methionine-PET CT-PET image fusion