2015 U N I V E R S I T I T E K N O L O G I P E T R O N A S

Size: px

Start display at page:

Download "2015 U N I V E R S I T I T E K N O L O G I P E T R O N A S"

Pierce Anthony
5 years ago
Views:

Multi-Modality based Diagnosis: A way forward by Hafeez Ullah Amin Centre for

Electronic Engineering 2015 U N I V E R S I T I T E K N O L O G I P E T R O N A

No part of this document may be reproduced, stored in a retrieval system or

1 Multi-Modality based Diagnosis: A way forward by Hafeez Ullah Amin Centre for Intelligent Signal and Imaging Research (CISIR) Department of Electrical & Electronic Engineering 2015 U N I V E R S I T I T E K N O L O G I P E T R O N A S All rights reserved. No part of this document may be reproduced, stored in a retrieval system or transmitted in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the permission of the copyright owner. 1

2 Outline Introduction Electroencephalography (EEG) Functional Magnetic Resonance Imaging (fmri) Positron Emission Tomography (PET) Magnetoencephalography (MEG) Functional Near Infrared Spectroscopy (fnirs) Recent Studies using multimodality approach Summary 2

3 Introduction What is multi-modality? combines two or more data sets collected with different imaging techniques with the objective of enhancing the understanding of brain functions. It also refers to fusion of different data sets. 3

4 Brain Imaging Modalities fmri fnirs MEG 4

Methods for Imaging Neural Activity electrical activity - excitatory - inhibitory - soma action potential electrophysiology EEG MEG metabolic response - ATP tightly

5 Methods for Imaging Neural Activity electrical activity - excitatory - inhibitory - soma action potential electrophysiology EEG MEG metabolic response - ATP tightly regulated - glucose consumption - oxygen consumption hemodynamic response - blood flow - blood volume - blood oxygenation FDG PET H 15 2 O PET fnir fmri Perfusion MRI 5

6 Electroencephalography (EEG) ANT Neuro eego MITSAR 6

7 EEG The electroencephalogram (EEG) measures the activity of large numbers (populations) of neurons. First recorded by Hans Berger in EEG recordings are noninvasive, painless, do not interfere much with a human subject s ability to move or perceive stimuli, are relatively low-cost. Electrodes measure voltage-differences at the scalp in the microvolt (μv) range. Voltage-traces are recorded with millisecond resolution great advantage over brain imaging (fmri or PET). 7

8 EEG Standard placements of electrodes on the human scalp: A, auricle; C, central; F, frontal; Fp, frontal pole; O, occipital; P, parietal; T, temporal. 8

9 EEG 9

10 EEG Many neurons need to sum their activity in order to be detected by EEG electrodes. The timing of their activity is crucial. Synchronized neural activity produces larger signals. 10

11 EEG EEG potentials are good indicators of global brain state. They often display rhythmic patterns at characteristic frequencies 11

12 EEG EEG suffers from poor current source localization and the inverse problem 12

13 EEG Strength and Limitations High temporal Resolution (accurate at recording fast changes in neuronal activity) Direct measurement of electrical activity Low cost, portable, long-term recordings Less subject to motion artifacts Low spatial resolution Poor current source localization 13

14 Magnetoencephalography (MEG) 14

15 MEG SIGNAL 15

16 MEG Measures changes in magnetic fields that accompany electrical activity. 16

17 EEG MEG Electrical signal Deep & shallow: radial and tangential sources Tricky to localize A relatively cheap technique Magnetic signal Mostly shallow: tangential sources Easier to obtain and localize But expensive Both: excellent temporal resolution 17

18 Functional Magnetic Resonance Imaging (fmri) 18

19 fmri fmri is a technique for measuring brain activity. detecting the changes in blood oxygenation and flow that occur in response to neural activity e.g. when a brain area is more active it consumes more oxygen and to meet this increased demand, blood flow increases to the active area. fmri can be used to produce activation maps showing which parts of the brain are involved in a particular mental process. 19

BOLD signal Oxygenated Hemoglobin Diamagnetic (no

fmri magnetic field Deoxygenated Hemoglobin

20 BOLD signal Oxygenated Hemoglobin Diamagnetic (no unpaired electrons or magnetic moment) No affect of fmri magnetic field Deoxygenated Hemoglobin Paramagnetic (significant magnetic moment) Changes in magnetic field (Thulborn et al., 1982; Ogawa, 1990) Nature Reviews Neuroscience 3, (February 2002) 20

21 Hardware for fmri Four Key Components Magnet (provides strong, homogenous static magnet field) The Gradient Coil (provides smaller, rapidly changing magnetic fields for spatial encoding of the spins in the volume being imaged) RF Transmitter Coil(RF pulse is used for excitation of nuclei and resultant resonance is also RF signal) RF Receiver Coil 21

22 fmri: Necessary Equipment 4T magnet gradient coil (inside) RF Coil Magnet Gradient Coil RF Coil Source: Joe Gati, photos 22

The Big Magnet Very strong 1 Tesla (T) = 10,000 Gauss Earth s magnetic field = 0.5 Gauss 4 Tesla = 4 x 10,000 0.

23 The Big Magnet Very strong 1 Tesla (T) = 10,000 Gauss Earth s magnetic field = 0.5 Gauss 4 Tesla = 4 x 10, = 80,000X Earth s magnetic field Continuously on Main field = B 0 Robarts Research Institute 4T x 80,000 = B 0 Source: 23

24 Advantages and Limitations of fmri Good spatial (2 mm) resolution (source localization) Poor time resolution (2-6 seconds) Slight danger to subjects Expensive Treatment induced changes such as radiation necrosis can be difficult to distinguish from recurrent tumor. Hence, to evaluate disease status with MRI in patients who have been treated is a challenge. 24

25 Positron Emission Tomography (P.E.T) 25

26 What is PET PET is a noninvasive, diagnostic imaging technique for measuring the metabolic activity of cells in the human body. It was developed in the mid 1970s and it was the first scanning method to give functional information about the brain. 26 Htt://

27 What is a Positron? A Positron is an anti-matter electron, it is identical in mass but has an apposite charge of +1. Positron can come from different number of sources, but for PET they are produced by nuclear decay. Nuclear decay is basically when unstable nuclei are produced in a cyclotron by bombarding the target material with protons, and as a result a neutron is released. 18-O + proton => 18-F + neutron In PET the target material is chosen so that the product of the bombardment decays to a more stable state isotope by emitting a positron, for instance 18-F has too many protons, so one of these protons decays into a neutron emitting in the process a positron an a neutrino. proton (+1 charge) => neutron (0 charge) + positron (+1 charge) + neutrino (0 charge) After decay, we re left with 18-O 27

determine where they came from, where the nucleus was when it

28 How do we detect photons (gamma rays)? PET detects these photons with a PET camera which allows to determine where they came from, where the nucleus was when it decayed, and also knowing where the nucleus goes in the body. 28

29 Uses of PET Scan To diagnose cancer Prepare for epilepsy surgery Help diagnose dementia if other tests and exams do not provide enough information Tell the difference between Parkinson disease and other movement disorders Several PET scans may be taken to determine how well you are responding to treatment for cancer or another illness. 29

30 Challenges with PET scan False results are possible on PET scan, especially, Blood sugar or insulin levels may affect the test results in people with diabetes. It is possible, though very unlikely, to have an allergic reaction to the radioactive substance. Some people have pain, redness, or swelling at the injection site. PET must be done by a radiologist who has specialized in nuclear medicine and has substantial experience with PET. 30

31 Functional Near Infrared Spectroscopy (fnirs) 31

32 Mechanisms of fnir: Overview fnir = functional Near InfraRed Measure changes in infrared light absorption and scattering Primary source of signal contrast [Hb] and [Hb0] Biological tissue is highly scattering in NIR window Primarily used in vivo as a spectroscopic modality Not used to produce true images DOT = Diffuse Optical Tomography Methods for accurate image reconstruction 32

33 Mechanisms of fnir: Absorption of [Hb] and [Hb0] Water Absorption Near infrared window ~ nm Water absorption is mimized Hemoglobin species are dominant absorbers [Hb] & [HbO] Absorption 33

34 Vascular Response fmri vs fnir fmri fnir Spatial Resolution 8-27 mm 3 Blobs 1-10 cm 3 Temporal Resolution Slow (1-2 sec) Fast (50 Hz) important? Measurement parameter Mix of blood volume, blood flow, and O 2 metabolism [Hb] and [HbO] 34

35 Research Studies with Multimodality Approach 35

36 36

37 37

38 38

39 39

40 40

41 PET-MRI 41

42 42

43 43

44 44

45 45

46 46

47 47

48 48

49 49

50 Summary Multimodality approach provides several advantages compared with standalone imaging system, such as both temporal and spatial resolution, source localization, and functions and structure of brain tissues. Hence, helping to diagnose the brain s disorders in a better way However, challenges are there, including: o cost, o expertise of more than one imaging techniques, o handling of large diverse nature of data, o and computational resources. 50

Magnetic resonance imaging MRI

Magnetic resonance imaging MRI Introduction What is MRI MRI is an imaging technique used primarily in medical settings that uses a strong magnetic field and radio waves to produce very clear and detailed