Lec2: Digital Images and Medical Imaging Modalities
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This document discusses an introductory lecture on digital images and medical imaging modalities. It provides background on several modalities including X-ray, ultrasound, computed tomography, magnetic resonance imaging, positron emission tomography, and diffusion weighted imaging. For each modality, it describes the basic physics principles, clinical applications, and examples of images. The document emphasizes that medical image analysis is an important and active area of research that can help address challenges in measurement, detection, and diagnosis.
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Lec2: Digital Images and Medical Imaging Modalities
- 1. MEDICAL IMAGE COMPUTING (CAP 5937) LECTURE 2: Digital Images and Medical Imaging Modalities Dr. Ulas Bagci HEC 221, Center for Research in Computer Vision (CRCV), University of Central Florida (UCF), Orlando, FL 32814. [email protected] or [email protected] 1SPRING 2017
- 2. Background Check • X-ray ? • Ultrasound? • ComputedTomography (CT)? • Magnetic ResonanceImaging (MRI)? • Positron Emission Tomography (PET)? • Diffusion Weighted Imaging (DWI)? • Diffusion Tensor Imaging (DTI)? • Magnetic Particle Imaging (MPI)? • Optical Coherence Tomography (OCT)? 2
- 3. Medical Imaging • The most direct way to see inside the human (or animal) body is cut it open (i.e., surgery) 3
- 4. Medical Imaging • The most direct way to see inside the human (or animal) body is cut it open (i.e., surgery) • We can see inside the human body in ways that are less invasive or (completely non-invasive) 4
- 5. Medical Imaging • The most direct way to see inside the human (or animal) body is cut it open (i.e., surgery) • We can see inside the human body in ways that are less invasive or (completely non-invasive) • We can even see metabolic/functional/molecular activities which are not visible to naked eye 5
- 6. Medical Imaging • The most direct way to see inside the human (or animal) body is cut it open (i.e., surgery) • We can see inside the human body in ways that are less invasive or (completely non-invasive) • We can even see metabolic/functional/molecular activities which are not visible to naked eye 6 Image Processing Image quality improvement Machine Learning Tissue types Image Understanding Semanticdescription & content understanding
- 7. Where do radiologists interpret scans? 7 •Dedicated light source •Darkened environment •Limited distraction
- 9. Medical Image Analysis • Because of the rapid technical advances in medical imaging technology and the introduction of new clinical applications, medical image analysis has become a highly active research field. 9
- 10. Medical Image Analysis • Because of the rapid technical advances in medical imaging technology and the introduction of new clinical applications, medical image analysis has become a highly active research field. • Improvements in image quality, changing clinical requirements, advances in computer hardware, and algorithmic progress in medical image processing all have a direct impact on the state of the art in medical image analysis. 10
- 11. Medical Image Analysis • Because of the rapid technical advances in medical imaging technology and the introduction of new clinical applications, medical image analysis has become a highly active research field. • Improvements in image quality, changing clinical requirements, advances in computer hardware, and algorithmic progress in medical image processing all have a direct impact on the state of the art in medical image analysis. • Medical images are often multidimensional (2D, 3D, 4D,nD), have a large dynamic range, are produced on different imaging modalities in the hospital, and make high demands upon the software for visualization and human–computer interaction. – A high resolution MR image of the brain, for instance, may consist of more than 200 slices of 512 x 512 pixels each, i.e., more than 50 million voxels in total. (100MB) – In clinical studies that involve the analysis of time sequences or multiple scans of many subjects, the amount of data to be processed can easily exceed 10 GB. – While 8 bits or 1 byte per pixel is usually sufficient in digital photography, most medical images need 12 bits per pixel (represented by 2 bytes in the computer memory). 11
- 12. Medical Image Analysis-Manual • Often accepted as surrogate of the truth (if biopsy or real ground truth is not available) • However, manual analysis is highly subjective because it relies on the observer’s perception. – Intra and inter-observer agreements/variabilities • It is highly tedious 12
- 13. Observer Variability – Example: Liver lesion 13 Intra- (one week interval) Inter-
- 14. Medical Image Analysis-Automated • Different strategies for image analysis exist. However, few of them are suited for medical applications. 14
- 15. Medical Image Analysis-Automated • Different strategies for image analysis exist. However, few of them are suited for medical applications. • The reason is that both the medical image data and the model or prototype (i.e., the a priori description of the features to be analyzed), are typically quite complex. 15
- 17. Digital Images 17 • Definition:A digital image is defined by integrating andsampling continuous (analog) data in a spatial domain [Klette, 2014].
- 18. Picture Elements (Pixels), Volume Elements (Voxels) 18 PIXELS are ATOMIC ELEMENTS of an image. In late 1960s, terminology ‘pixel’ was introduced by a group of scientist at JPL in California!
- 19. Image Types 19 • A scalar image has integer values a: level (bit) Ex. If 8 bit (a=8), image spans from 0 to 255 0 black 255 white Ex. If 1 bit (a=1), it is binary image, 0 and 1 only. u 2 {0, 1, ..., 2a 1}
- 20. Image Types-Color 20 • Image has three channels (bands), each channel spans a-bit values. • RGB, Hue-Saturation- Brightness
- 21. Brief Introduction to Imaging Modalities 21
- 22. 22 ELECTROMAGNETIC SPECTRUM (P. Suetens)
- 23. X-Ray Imaging / Radiography • The first published medical image was a radiograph of the hand of Wilhelm Conrad Roentgen’s wife in 1895. Nobel Prize in Physics 1901. 23 routine diagnostic radiography (2D images): chest x-rays, fluoroscopy, mammography,motion tomography, angiography,…
- 24. X-Ray Imaging / Radiography 24 Iin Iout D = log( Iin Iout ) D=Optical density E=exposure (Iin/Iout) Iin=incoming light intensity Iout=outgoing light intensity
- 25. X-Ray Imaging / Radiography-Sensitometric Curve 25 Linear part (useful!) • Maximum slope of the curve is known as the gamma of the film. • A larger slope implies a higher contrast at the cost of a smaller useful exposure range • In low and high density areas, contrast is low and little information available. • In linear part, slope characterize Contrast of the film. Max slope is known as Gamma of the film. Defn. Contrast: is the intensity difference in adjacent regions of the image.
- 26. Basics Use of X-Rays • Dental examinations • Surgical markers prior to invasive procedures • Mammography • Orthopedic evaluations • Chest examination (Tuberculosis) • Age estimation (forensic, left hand) 26
- 27. Clinical Examples – X-Rays 27 PELVIS ELBOW
- 28. How Radiologists SearchAbnormal Patterns in Chest X-Rays? 28 Patterns belonging to Potentially Benign Lesions Patterns belonging to Potentially Malignant Lesions
- 29. How Radiologists SearchAbnormal Patterns in Chest X-Rays? 29 Radiologists often report the following • Size, dimension, volume • Pattern description, • Location, • Interaction with Nearby structures, • Intensity distribution • Shape • … Difficulties • Noise • vessels can be seen as small nodules • radiologists may miss the pattern • patterns may not be diagnostic • CT often required for betterdiagnosis • size estimation is done manually in 2D • Shadowing • total lung capacity computation
- 30. How Radiologists SearchAbnormal Patterns in Chest X-Rays? 30 Radiologists often report the following • Size, dimension, volume • Pattern description, • Location, • Interaction with Nearby structures, • Intensity distribution • Shape • … Difficulties • Noise • vessels can be seen as small nodules • radiologists may miss the pattern • patterns may not be diagnostic • CT often required for betterdiagnosis • size estimation is done manually in 2D • Shadowing • total lung capacity computation Computer algorithms can solve/simplify these problems for improved healthcare
- 31. Another Example for X-ray Imaging 31 Benign Malignant
- 32. Ultrasound Imaging • US is defined as any sound wave above 20KHz 32 1794-Lazzaro Spallanzani- Physiologist First to study US physics by deducing bats used to US to navigate by echolocation. 1826-Jean Daniel Colladon - Physicist Uses church bell (early transducer) under water to calculate speed of sound through water prove sound traveled faster through water than air. 1880-Pierre&Jacques Curie discover the Piezo-Electric Effect (ability of certain materials to generate an electric charge in response to applied mechanical stress.
- 33. 33 1942-Karl Dussik - Neurologist First physician to use US for medical diagnosis 1948-George Ludwig - MD First described the use of US to diagnose gallstones 1958-Ian Donald Pioneers in OB-GYN US Imaging Technology
- 34. Principle of US Imaging 34 Sound source Point source US equipment assumes that sound velocity is constant in the body. Ultrasonic Probe Human Body Ultrasonic Beam Reflected Signal
- 35. Features of US Imaging • Resolution: – direction of pulse propagation,pulse width 1-2mm – direction of scanning:beam width 2-3mm – low resolution and low SNR in deep region • Ability of imaging soft tissue • imaging in real time • Doppler image • Artefacts 35 Color flow mapping shows simultaneous amplitude (US) and velocity information (doppler)
- 36. Clinical Use of US Imaging 36
- 37. Clinical Use of US Imaging 37 Renal Artery Blood Flow manual measurements? can computer help calculating all blood flow and identify automatically the abnormal regions? (See Next Lecture, afternoon) stenosis is seen eca: external carotid artery cca: common carotid artery ica: internal carotid artery
- 38. Clinical Use of US Imaging 38 Bone, fat, and physical length Measurements –unborn babies (Image Credit: S. Rueda, Oxford Univ.)
- 39. Computed Tomography (CT) 39 Tomo:slice/level (Greek) Graphe: draw
- 40. CT Imaging (continue) 40 C-arm CT Micro-CT ~CAT Scan (computerized Axial tomography)
- 41. 3D Nature of CT 41
- 43. 3D Images 43 x y z I: Image I(x,y,z) denotes intensity value at pixel location x,y,z Note also that whatever you see on the left is right part of the body!
- 44. Clinical Use of CT Imaging • Standard imaging technique in many organs, particularlygold standard for lung imaging • Fast • Radiation exposure • Often used in surgery rooms • Show anatomy and pathology • Intensity values are (more-or-less) fixed, read as HU (Hounsfield Unit) 44
- 45. CT Imaging Example: Tumor 45 2D manual measurement of tumor size (short and long axis of tumor)
- 46. CT Imaging Example: Lung 46 (A)$Normal$ $(B)$Emphysema $(C)$Ground$Glass$Opacity$ (D)$Fibrosis $(E)$Micronodules $(F)$Consolida?on$
- 47. CT Imaging Example: Cardiac 47 how to calculate the amount of fluid? Fluid
- 48. Magnetic Resonance Imaging (MRI) • 1882-Nichola Tesla • Discovered rotating magnetic field • 1971-Paul Lauterbur NOBEL PRIZE • First invented MRI • Late 1970-Sir Peter Mansfield (Nottingham) NOBEL PRIZE • Developed mathematical techniques to create clearer images and also in minutes rather than hours as Lauterbur did. • CT is more widely used than MRI. • MRI does not have ionizing-radiation. • MRI has excellent soft tissue contrast, while CT is preferred for lung and bone imaging. • CT is fast (few seconds), while MRI is slow (sparse MRI ~5-10 mins, abdomen or brain may take 30-40 mins). 48
- 49. MRI Basics 49
- 51. Types of MRI 51
- 52. Brain MRI 52
- 53. Safety in MRI 53
- 54. Diffusion Tensor Imaging (DTI) 54 •MRI (sub-)modality •measures random Brownian motion of water molecules. •useful for tumor characterization (densely cellulartissues exhibit lower diffusion).
- 55. MRI Physics (Recap) • MR fields generatedby spinningelectrons are stronger then those created by spinningprotons. • However, hydrogenatoms take the right amount of energy (than the electrons) for their spins to be flipped against the appliedmagnetic field with a radio frequency (RF). • See WebCourse for additional links for imaging physics of MRI! 55
- 56. Diffusion Weighted Imaging (DWI) 56 Glioblastoma Tumor
- 58. Clinical Use: Example 58 Myocardial Infarction Detection
- 59. Clinical Use: Example 59 rectal tumor
- 60. Functional MRI (fMRI) • measures brain activity through oxygen concentration in the blood flow. • relies on the fact that cerebral blood flow and neuronal activation are coupled. • when area of the brain is active (in use), blood flow to that area also increases. • which part/location of the brain is activated when reading? • which part/location of the brain is activated when listening music? • which part/location of the brain is activated when searching puzzle? 60
- 62. Nuclear Medicine Imaging – PET/SPECT • Scint: Scintigraphy, two-dimensional images • PET: Positron Emission Tomography • SPECT: Single Photon EmissionTomography 62
- 63. Nuclear Medicine Imaging – PET/SPECT 63
- 64. Basics of PET Imaging • uses short-lived positron emitting isotopes (produced by collimators) • two gamma rays are produced from the annihilation of each positron and can be detected by specialized gamma cameras • resulting image show the distribution of isotopes • an agent is used to bind into isotopes (glucose, …) 64 Late 1950s, David L. Kuhl concept of emission and transmission molecular activity is measured.
- 65. PET/CT and MRI/PET (Hybrid Imaging) 65 PET/CT -choice of modality for oncological applications(yet) MRI/PET -superior soft tissue contrast resolution -minimized radiation
- 66. What to Measure in PET? • SUV (standardized uptake value: voxel-wise or region- wise) (SUVpeak, SUVmax, SUVlbm) • Metabolic lesion/tumor volume (MTV) • Shape information of (functional) lesion (spiculated vs focal) • Texture information of lesion (heterogeneous vs homogeneous) • Number and distribution of the lesions (focal, multi-focal) 66
- 67. Clinical Use of PET: Example 67
- 68. Clinical Use of PET: Example 68
- 69. Serial and Simultaneous MRI/PET 69 Past Now!
- 70. Shallow Comparison of Imaging Methods 70 Chest Abdomen Head/Neck Cardiovascul ar Skeletal/mus cular CT gold standard Need contrast for excellency, widely used Good for trauma Gold standard Gold standard US no use except heart or P.Effusion Problems with gas Poor Poor Elastography Nuclear Extensive use in heart and therapy in lung CT or MRI is merged PET Perfusion bone marrow MRI growing cardiac applications Increased role of MRI Gold standard Will replace ct in near future Excellent
- 71. Summary • Medical image analysis/computingis a highly active research field. • Measurement is the key in MIC! Volumetry, morphometry, quantification, visualizationare all necessary methods in diagnostic radiology applications. • Different imaging modalities are in use for different clinical purpose(s) • Imaging modalities have distinct properties from each other 71
- 72. References and Slide Credits • P. Suetens, Fundamentals of Medical Imaging, CambridgeUniv. Press. • ITK.org • siemens.com • slicer.org • Read the additionallecture notes given in the web- course and course webpage. • When you send email, please put “MIC:…” into subject line 72
- 73. Questions? 73
- 74. Quiz! • 1 pt 74