Imaging Techniques. Introduction. Patrícia Figueiredo IST

Transcription

1 Imaging Techniques Introduction Patrícia Figueiredo IST

2 Faculty: Patrícia Figueiredo, IST IST North Tower, 6th floor, Tel: ext 2277) Jorge Campos, FMUL Serviço de Imagiologia Hospital Santa Maria Piso 3 Rosa Barroca, Tel: ) Objectives: By the end of the semester, the student should be familiar with: the physical principles and basic instrumentation used for the acquisition of the main biomedical imaging techniques; the most important image reconstruction and analysis methods; the main applications in disease diagnosis and monitoring. Bibliography: Principal: - Introduction to Biomedical Imaging. Andrew Webb. Secondary: - Foundations of Medical Imaging. Zang-Hee Cho, Joie P. Jones, Manbir Singh. - Medical Imaging Physics. William R. Hendee, E. Russell Ritenour. - Biosignal and Biomedical Image Processing: Matlab-Based Applications. John L.Semmlow. - Imagiologia Básica Texto e Atlas, Ed. João Martins Pisco, LIDEL Julho 2009.

3 Program: 1. Introduction 1. Historical perspective 2. General imaging principles 2. X ray imaging 1. X rays 2. Planar radiography 3. Computed Tomography (CT) 4. Image reconstruction 5. Specialized imaging techniques 3. Nuclear medicine imaging 1. Radionuclides 2. Scintigraphy 3. Single Photon Emission Computed Tomography (SPECT) 4. Positron Emission Tomography (PET) 4. Magnetic Resonance Imaging (MRI) 1. Nuclear Magnetic Resonance (NMR) 2. Image formation and reconstruction 3. Instrumentation 4. Constrast mechanisms 5. Imaging sequences 6. Rapid imaging 7. Specialized imaging techniques 5. Ultrasound imaging 1. Ultrasounds 2. Transducers 3. Imaging modes

4 Evaluation method: Two tests or Final exam - 50% (IST) (the 2 nd test will coincide with the first part of, and take place on the same date as, the 1 st exam). Lab work - 30% (IST) Essay - 15% (FMUL) Assiduity to FMUL classes 5% (FMUL) A minimum grade of 9.5 is required for the tests/exam and the lab work. IST Labs: - Lab work is carried out in groups of 2 students, split into 3 shifts of 10 groups each: A - Wednesdays, 14h00 15h30; B Wednesdays, 15h30 17h00; and C Wednesdays, 17h00 18h30. - Lab guidelines will be published on Thursdays before each Lab. - Lab reports should be handed in to the IST lecturer at the end of each lab class. FMUL Site visits and essay: - The FMUL site visits are performed in 4 shifts of ~15 students each: I 15/05, 14-16h; II 15/05, 16-18h; III 22/05, 14-16h and IV 22/05, 16-18h. - The essay will be written in groups of ~4 students each (pairs of lab groups); - The essay should be handed in to the FMUL lecturer by 24/05. Groups and shifts: - The students should organize themselves into IST lab groups, IST lab shifts, FMUL essay groups and FMUL site visit shifts; and the student delegate should send the respective lists to patricia.figueiredo@ist.utl.pt by 22/02.

5 Schedule: Labs are in Room QLTI, South Tower 5 th floor

6 On Fenix! (check Announcements and section Materials)

7 Introduction 1. Historical perspective of medical imaging a) From the first x ray image b) to PET-MR 2. Definition and classification of medical imaging modalities a) Definition and scope b) Classification according to different criteria 3. Basic principles of medical imaging a) Image properties b) Imaging principles c) Visualization methods and image processing

8 Röntgen, discovery of X rays and the first radiography, Würzburg (1895) Within a month of their discovery, x rays were being explored as medical tools in several countries

9 London(1896)

10 Technical developments leading to radiography today -hot-cathode x-ray tubes -rotating anodes - intensifying screens - image intensifiers -contrast agents - -computed radiography -digital radiography - angiography -

11 Radon and the Radon transform (1917) R { f ( x, y) } = f ( x( l), y( l) )dl L

12 Hounsfield and the first CT prototype at EMI Ltd., England (1972) EMI Ltd., the commercial developer of CT, was the first company to enter CT into the market. They did so as a last resort, only after offering the rights to sell, distribute, and service CT to the major vendors of imaging equipment. The vendors rejected EMI s offer because they believed the market for CT was too small

13 The successive generations of CT: 1st, 2nd, 3rd, 4th,

14 A 3rd generation CT scanner today T = X-ray tube D = X-ray detector X = X-ray fan beam R = Rotation direction

15 CT images today

16 Becquerel and the discovery of spontaneous radioactivity (1896) α decay

17 The discovery of Tc and the synthesis of artificial radionuclides (1937)

18 Anger and the scintillation camera (or γ camera), 1952

19 Positron Emission Tomography, PET (1953) Isótopos emissores de positrões

20 Single Photon Emission Computed Tomography, SPECT (1963) 99m-Tc T1/2= ~ 6 h I-123 T1/2= ~ 13 h

21 Molecular imaging today

22 Molecular imaging today Oncology Neurotransmitters

23 Bloch and Purcell and the discovery of Nuclear Magnetic Resonance, NMR (1945) B 0 ω L B 0 Isotope Spin I γ [MHz/T] Natural abundance [%] 1 H ½ H F ½ P ½

24 Lauterbur and the first MR images - zeugmatography (1973) One would not think from reading the title that it represented the foundation for a revolution in imaging. Indeed the paper was nearly not published having been initially rejected by the editor as not of sufficiently wide significance for inclusion in Nature.

25 Ernst and Fourier reconstruction of MR images (1975) 2DFT Jean-Baptiste-Joseph Fourier K space

26 Ernst and Fourier reconstruction of MR images (1975) 2DFT Brain slice K space

27 Damadian and the first whole body images (1977) In 2003, The Noble Prize for the MRI was awarded, not to Dr. Damadian, but to two nuclear magnetic resonance scientists Paul Lauterbur and Peter Mansfield.

28 Mansfield and the acquisition of ultra-fast MR images (1977)

29 From Nuclear Magnetic Resonance (NMR) to Magnetic Resonance Imaging (MRI) 1946 MR phenomenon - Bloch & Purcell 1952 Nobel Prize - Bloch & Purcell NMR developed as analytical tool Computerized Tomography 1973 Backprojection MRI - Lauterbur 1975 Fourier Imaging - Ernst 1977 Echo-planar imaging - Mansfield 1986 Gradient Echo Imaging 1987 MR Angiography - Dumoulin 1991 Nobel Prize - Ernst 1992 Functional MRI 2003 Nobel Prize - Lauterbur & Mansfield

30 MRI today

31 MRI today Hardenbergh et al., 2005

32 MRI today: going up the field strength T, 3T, 7T Super-conducting magnets: liquid helium fill for cooling shielding of large fringe field

33 Leonardo Da Vinci was the first to compare sound reflection to light reflection (1480) The sonar was developed only during the 2nd World War (1940s)

34 Ultrasound and echography (1953) In May 1953 they produced real-time images at 15 MHz of cancerous growths of the breast. They had also coined their method 'echography' and 'echometry...

35 Ultrasound and echography (1953)

36 Utrasounds today

37 Trends in medical imaging From To Analog Digital Qualitative Quantitative Anatomic Physiobiochemical Static Dynamic Nonspecific Tissue-Targeted Diagnosis Diagnosis/Therapy Single modality Hybrid systems

38 PET-CT

39 PET-MR RF shield gantry phantom head coil Protótipo Siemens Medical, Grazioso et al., 2005 Prototype from the Cambridge PET/MR project Animal MR system PET Detectors MR Receiver Coil Cherry, University of California, Davis

40 Medical imaging definition and scope

41 Medical imaging definition in Cho et al.: Medical imaging refers to the study of the interaction of all forms of radiation with biologicak tissues and the development of appropriate technology for the extraction of clinically useful information from the observation of these interactions. Medical imaging in wikipedia.org: As a discipline and in its widest sense, it is part of biological imaging and incorporates radiology (in the wider sense), radiological sciences, endoscopy, (medical) thermography, medical photography and microscopy (e.g. for human pathological investigations). Measurement and recording techniques which are not primarily designed to produce images, such as electroencephalography (EEG) and magnetoencephalography (MEG) and others, but which produce data susceptible to be represented as maps (i.e. containing positional information), can be seen as forms of medical imaging.

42 Main medical imaging modalities: - Radiography, Angiography, Fluoroscopy, Mammography (X-rays) - Computed Tomography (CT) (X-rays) - Single Photon Emission Computed Tomography (SPECT) (nuclear medicine) - Positron Emission Computed Tomography (PET) (nuclear medicine) - Magnetic Resonance Imaging (MRI) - Ecography, Echo-Doppler (ultrasound) - Diffusion Optical Imaging (DOI) (optical imaging) - Optical Coherence Tomography (OCT) (optical imaging) - Confocal laser microscopy (optical imaging) -Electric impedance tomography (EIT) - Electro-encephalography (EEG) (neurophysiology) - Magneto-encephalography (MEG) (neurophysiology)

43 As a function of the type of radiation: - X-rays: Radiography, CT, Angiography - γ photons: PET, SPECT - Radiofrequencies (RF): MRI, fmri - Ultrasound (US): Echography, Echo-Doppler

44 As a function of the type of radiation: - X-rays: Radiography, CT, Angiography - γ photons: PET, SPECT - Radiofrequencies (RF): MRI, fmri - Ultrasound (US): Echography, Echo-Doppler As a function of the observed process: - transmission: X-rays (Radiography, CT) - emission: PET, SPECT - reflexion: Ultrasound (Echography, Echo-Doppler) - magnetic resonance: MRI, fmri

45 As a function of the ionizing nature of the radiation: - ionizing (E>13.6 ev): X-rays, PET, SPECT Specific Ionization (SI), Quality Factor (QF), Dose - non-ionizing (E<13.6 ev): Ultrasound, MRI Dielectric constant, Specific Absorption Rate (SAR)

46 As a function of the ionizing nature of the radiation: - ionizing (E>13.6 ev): X-rays, PET, SPECT Specific Ionization (SI), Quality Factor (QF), Dose - non-ionizing (E<13.6 ev): Ultrasound, MRI Dielectric constant, Specific Absorption Rate (SAR) As a function of invasiveness: - invasive: X-rays, PET, SPECT - non-invasive: Ultrasound, MRI

47 As a function of the method of image production: - Classic: the image is a direct manifestation of the interaction between the radiation and the object (Radiography, Echography) - Modern: the image is obtain from the observations through some computation leadin to the so-called image reconstruction (CT, PET, SPECT, MRI, Echo-Doppler) As a function of quantitativeness: - Non-quantitative (Radiography, Echography) - Quantitative (CT, PET, SPECT, MRI, Echo-Doppler )

48 As a function of the type of information obtained: - structural: Radiography, CT, Echografia, MRI - functional: Angiography, PET, SPECT, Echo-Doppler, fmri - dynamic (blood flow): Angiography, Echo-Doppler - physiological (diffusion, perfusion): fmri, PET, SPECT - metabolic: MRSI, PET, SPECT - molecular: PET, SPECT,

49 As a function of spatial and temporal resolution: neuralmusic/neural-activity-work.html CT MRI SPECT PET fmri EEG PET-MRI (fusion) MEG-MRI (superimposed)

50 Imaging principles

51 Image orientation Image properties

52 Image properties Image volume, slice, voxel and field-of-view (FOV) Image prescription slice volume FOV 2D image

53 Image properties Spatial resolution Image resolution ~ pixel size Image resolution = smallest distance between two point sources for which the sources can be resolved. Image resolution depends on the imaging system and parameters used.

54 Image properties Spatial resolution Image resolution ~ pixel size

55 Spatial frequency Image properties

56 Image properties Image contrast Image contrast = difference in image intensity that makes an object distinguishable from another or from the background. Image contrast depends on the tissue characteristics as well as the contrast sensitivity of the imaging system used.

57 Image contrast Image properties

58 Image properties Signal-to-noise-ratio (SNR): SNR ~ compares the level of a desired signal to the level of background noise. Signal processing definition: (power of signal over power of noise) Medical imaging definition: (mean signal over SD of noise) Image SNR depends on the available object signal and on the imaging system noise characteristics. SNR Noise

59 Signal-to-noise-ratio (SNR): Image properties

60 Image properties Contrast-to-noise ratio (CNR): CNR ~ compares the image contrast between regions-of-interest A and B to the level of background noise. Image CNR depends on the tissue contrast, the object size and the contrast sensitivity, image resolution and SNR of the imaging system.

61 Image properties Main image characteristics: Spatial resolution = minimum point separation (R): PSF, LSF, MTF Signal-to-noise-ratio (SNR): Object, Noise Contrast-to-noise ratio (CNR): Object, Noise, PSF CT, PET, SPECT: SNR = N σ N N = número de raios X ou γ, com distribuição de Poisson, σ = desvião padrão MRI: SNR = s, SNR σ ξ N SNR N s = sinal médio; σ ξ = desvio padrão do erro, N = número de repetições

62 The imaging process Imaging principles

63 Imaging principles In general: ( x, y) = S{ O( x, y) } + N( x y) I, I ( x y) S O( x, y ) δ ( x x, y y ) dx dy N( x, y), = (x 0,1,y 0,1 ) System (x 0,1,y 0,1 ) (x 0,2,y 0,2 ) Object Noise (x 0,2,y 0,2 ) Image

64 Imaging principles For a spatially invariant system : I ( x y) O( x, y ) PSF( x x, y y ) dx dy N( x, y), = + ( x, y) = O( x, y) PSF( x, y) Noise I + PSF = Point Spread Function Determinant factors (depend on modality): h total = h sensor h sampling h reconstruction h filtering Ideal PSF: h(x,y,z) = δ(x,y,z) I = O, δ = Delta de Dirac. Most common PSF shapes: Gaussian, sinc,...

65 Imaging principles Point spread function (PSF): ( x, y) = O( x, y) PSF( x, y) Noise I + Linear spread function (LSF): ( y) LSF = PSF( x, y) dx PSF(x,y) LSF(y) x

66 Imaging principles Spatial resolution R = smallest distance between two point sources for which the sources can be resolved. R is related with the system point spread function (PSF): A common shape for the PSF is a Gaussian - in 1D: (in this case, R~FWHM in each direction) The total imaging PSF results from several contributions:... and so does the final image resolution: I ( x, y, z) = PSF( x, y, z) O( x, y, z) 2 1 ( x µ ) h( x) = 2πσ FWHM = 2 PSF R final total = = R PSF 2ln 1 exp ( 2σ ) + + R 2 N σ σ PSF N,

67 Imaging principles Modulation transfer function (MTF): MTF = Amp FT [ ( PSF) ] = Amp PSF( x, y) [ ] i2πk x i2πk y e e dxdy x y

68 Image processing Medical image digital formats: Digital Imaging and Communications in Medicine (DICOM) = standard for handling, storing, printing, and transmitting information in medical imaging. AVW Analyze = data format used by the image processing program written by The Biomedical Imaging Resource at the Mayo Foundation, now extended to a wide variety of other software. Neuroimaging Informatics Technology Initiative (NIfTI) = to speed the development and enhance the utility of informatics tools related to neuroimaging.

69 Image processing Medical image visualization and processing tools: Manufacturers: e.g., Siemens Medical

70 Image processing Medical image visualization and processing tools: Freeware tools: - General purpose software: e.g. ImageJ - Specialized software: e.g., MRIcro

71 Image processing Medical image development tools: Matlab Image Processing Toolbox Description Topics Image Acquisition, Import, and Export Image Processing, Analysis, and Visualization Algorithm Development and Application Deployment Video and Image Processing System Design Geospatial Computing Medical Imaging

72 References Webb, Introduction to Biomedical Imaging, Wiley Cho, Jones, Singh, Foundations of Medical Imaging. Hendee, Medical Imaging Physics, Wiley Sprawls, Physical Principles of Medical Imaging. Changing the Landscape: How Medical Imaging Has Transformed Health Care in the U.S.. National Electrical Manufacturers Association, December 2006.