ELECTRICAL ENGINEERING DEPARTMENT

Spring 2012

EE 5359-002 (DE) – Multimedia Processing

Project Report On

MEDICAL IMAGING

GUIDED BY: DR. K.R.RAO

SUBMITTED BY:

AnujaKulkarni(1000722132)

MEDICAL IMAGING

ABSTRACT

Medical imaging[1] as the name suggests is the technique and process used to createimagesof parts and functions of human body for clinical purposes. It is a medical procedureseeking to reveal,diagnoseor examinedisease.

As a discipline, it is part ofbiological imagingand incorporatesradiology,nuclear medicine, investigativeradiological sciences,endoscopy, (medical)thermography, medical photography andmicroscopy(e.g. for human pathological investigations).As a field of scientific investigation, medical imaging constitutes a sub-discipline ofbiomedical engineering,medical physicsormedicinedepending on the context.

This project mainly covers three topics of medical imaging i.e. creation of 3D images, compression of medical images and non-diagnostic imaging, its evaluation and implementation.

List of acronyms

CAT - Computed Axial Tomography

CT - Computed Tomography

DICOM - Digital Imaging and Communications in Medicine

EEG - Electroencephalography

EKG - Electrocardiography

fMRI- Functional Magnetic Resonance imaging

JFIF- JPEG File Interchange Format

JPEG- Joint Photographic Experts Group

JPIP- JPEG 2000 Interactive Protocol

MEG - Magnetoencephalography

MRI - Magnetic Resonance Imaging

NMR- Nuclear Magnetic Resonance

PET - Positron Emission Tomography

PNG- Portable Network Graphics

RF- Radio Frequency

SSIM- Structural Similarity

Introduction

Medical imaging[1]is the technique and process used to createimagesof thehuman bodyfor clinical purposes. Although imaging of removedorgansandtissuescan be performed for medical reasons, such procedures are not usually referred to as medical imaging, but rather are a part ofpathology.

As a discipline and in its widest sense, it is part ofbiological imagingand incorporatesradiology,nuclear medicine, investigativeradiological sciences,endoscopy, medical photography andmicroscopy.

Measurement and recording techniques which are not primarily designed to produceimages, such as-

  1. Electroencephalography(EEG)
  2. Magnetoencephalography(MEG)
  3. Electrocardiography(EKG)

and others but which produce data susceptible to be represented asmaps(i.e. containing positional information), can be seen as forms of medical imaging.

Up until 2010, 5billion medical imagingstudieshave been conducted worldwide [1].Radiation exposure from medical imaging in 2006 made up about 50% of total ionizing radiation exposure in the United States.[1]

There are two types of medical imaging [1], they are-

  1. Invisible light medical imaging
  2. Visible light medical imaging

In the clinical context, "invisible light" medical imaging is generally equated toradiologyor "clinical imaging" and the medical practitioner responsible for interpreting the images is aradiologist.

"Visible light" medical imaging involves digital video or still pictures that can be seen without special equipment. Dermatology and wound care are two modalities that utilize visible light imagery. Diagnosticradiographydesignates the technical aspects of medical imaging and in particular the acquisition of medical images. Theradiographerorradiologic technologistis usually responsible for acquiring medical images of diagnostic quality, although some radiological interventions are performed byradiologists. While radiology is an evaluation of anatomy, nuclear medicine provides functional assessment.

As a field of scientific investigation, medical imaging constitutes a sub-discipline ofbiomedical engineering,medical physicsormedicinedepending on the context: Research and development in the area of instrumentation, image acquisition (e.g.radiography), modelling and quantification are usually the preserve ofbiomedical engineering,medical physicsandcomputer science; Research into theapplicationand interpretation ofmedical imagesis usually the preserve ofradiologyand the medical sub-discipline relevant to medical condition or area of medical science i.eneuroscience,cardiology,psychiatry,psychology, etc. under investigation.

Medical imaging is often perceived as the set of techniques that noninvasively produce images of the internal aspect of the body. In this restricted sense, medical imaging can be seen as the solution ofmathematicalinverse problems. This means that cause is inferred from effect. In the case of ultrasonography [2] the probe consists of ultrasonic pressure waves and echoes inside the tissue show the internal structure. In the case of projection radiography, the probe isX-rayradiationwhich is absorbed at different rates in different tissue types such as bone, muscle and fat. [2]

The term non-invasive is a term based on the fact that medical imaging modalities do not penetrate the skin physically. But on the electromagnetic and radiation levels, they are quite invasive. From the high energy photons in X-Ray computed tomography, to the 2+ Tesla coils of an MRI device, these modalities alter the physical and chemical environment of the body in order to obtain data.

Imaging Technologies:

  1. Radiography [5]

Two forms of radiographic images are in use in medical imaging; projection radiography and fluoroscopy.[6]

Fluoroscopyproduces real-time images of internal structures of the body in a similar fashion toradiography, but employs a constant input of x-rays, at a lower dose rate.

Figure 1 shows an example of digital radiography i.e fluoroscopy

Projectional radiographs, more commonly known as x-rays, are often used to determine the type and extent of a fracture as well as for detecting pathological changes in the lungs.

Figure 1: Digital radiography [7]

  1. Magnetic Resonance Imaging (MRI)

A magnetic resonance imaging instrument [8] (MRI scanner), or "nuclear magnetic resonance (NMR) imaging" scanner as it is originally known, uses powerful magnets to polarize and excitehydrogennuclei (singleproton) in water molecules in human tissue, producing a detectable signal which is spatially encoded, resulting in images of the body. The MRI machine emits an RF (radio frequency) pulse that specifically binds only to hydrogen.

LikeCT, MRI traditionally creates a two dimensional image of a thin "slice" of the body and is therefore considered atomographicimaging technique. Modern MRI instruments are capable of producing images in the form of 3D blocks, which may be considered a generalization of the single-slice, tomographic concept.

Figure 2 shows afMRI scan showing regions of activation in orange, including theprimary visual cortex

Figure 2: A fMRI scan [9]

  1. Fiduciary Markers

Fiduciary markers [10] are used in a wide range of medical imaging applications. Images of the same subject produced with two different imaging systems may be correlated by placing a fiduciary marker in the area imaged by both systems. In this case, a marker which is visible in the images produced by both imaging modalities must be used. By this method, functional information frompositron emission tomographycan be related to anatomical information provided bymagnetic resonance imaging(MRI). Similarly, fiducial points established during MRI can be correlated with brain images generated bymagnetoencephalographyto localize the source of brain activity.

Fiducial markers also have other applications for example indoor positioning and navigation. [11]

Figure 3 shows an example of fiduciary markers taken from reacTIVision.

Figure 3: Fiducialmarker example [12]

ReacTIVision is an open source, cross-platform computer vision framework for the fast and robust tracking of fiducial markers attached onto physical objects, as well as for multi-touch finger tracking.

4.Photo acoustic imaging

Photoacoustic imaging [13] is a recently developed hybrid biomedical imaging modality based on the photoacoustic effect. It combines the advantages of optical absorption contrast with ultrasonic spatial resolution for deep imaging in (optical) diffusive or quasi-diffusive regime. Recent studies have shown that photoacoustic imaging can be used in vivo for tumor angiogenesis monitoring, blood oxygenation mapping, functional brain imaging, and skin melanoma detection, etc.

  1. Tomography [14]

Tomographyis the method of imaging a single plane, or slice, of an object resulting in atomogram. There are several forms oftomography like

  • Linear tomography
  • Poly tomography
  • Zonography
  • Orthopantomography
  • Computed tomography [15]

X-raycomputed tomography, alsocomputed tomography(CT) orcomputed axial tomography(CAT), can be used formedical imagingand industrial imaging methods employingtomographycreated by computer processing.Digital geometry processingis used to generate athree-dimensionalimage of the inside of an object from a large series of two-dimensionalX-rayimages taken around a singleaxis of rotation.

CT produces a volume of data that can be manipulated, through a process known as "windowing", in order to demonstrate various bodily structures based on their ability to block the X-ray beam.

Figure 4 shows computed tomographyof humanbrain, frombase of the skullto top, taken with intravenous contrast medium.

Figure 4: Computed tomography of brain [16]

  1. Ultrasound [17]

Medical ultra-sonographyuses high frequencybroadbandsound waves in themega Hertzrange that are reflected by tissue to varying degrees to produce (up to 3D) images.Ultrasound is also used as a popular research tool for capturing raw data, that can be made available through anultrasound research interface, for the purpose of tissue characterization and implementation of new image processing techniques.

Creation of three-dimensional images

Recently, techniques have been developed to enable CT, MRI and ultrasound scanning software to produce 3D images for the physician.Traditionally CT and MRI scans produced 2D static output on film. To produce 3D images, many scans are made, then combined by computers to produce a 3D model, which can then be manipulated by the physician. 3D ultrasounds are produced using a somewhat similar technique [18]. In diagnosing disease of the viscera of abdomen,ultrasound is particularly sensitive on imaging of biliary tract, urinary tract and female reproductive organs (ovary,fallopian tubes). As for example,diagnosis of gall stone by dilatation of common bile duct and stone in common bile duct. With the ability to visualize important structures in great detail, 3D visualization methods are a valuable resource for the diagnosis and surgical treatment of pathologies. The 3D equipment was used previously for similar operations with great success. [19]

Other proposed or developed techniques include:

Diffuse optical tomography

Elastography

Electrical impedance tomography

Optoacoustic imaging

Ophthalmology

  • A-scan
  • B-scan
  • Corneal topography
  • Optical coherence tomography
  • Scanning laser ophthalmoscopy

Some of these techniques are still at a research stage and not yet used in clinical routines.

Compression of medical images

Medical imaging techniques produce very large amounts of data, especially from CT, MRI and PET modalities. As a result, storage and communications of electronic image data are prohibitive without the use of compression.JPEG 2000is the state-of-the-art image compressionDICOMstandard for storage and transmission of medical images. The cost and feasibility of accessing large image data sets over low or various bandwidths are further addressed by use of another DICOM standard, calledJPIP, to enable efficient streaming of theJPEG 2000compressed image data.[1]

  1. JPEG2000

JPEG 2000is animage compressionstandard and coding system. It was created by thejoint photographic experts groupcommittee in 2000 with the intention of superseding the originaldiscrete cosine transform-basedJPEGstandard (created in 1992) with a newly designed,wavelet-based method. [20]

The standardizedfilename extensionis.jp2forISO/IEC15444-1 conforming files and.jpxfor the extended part-2 specifications, published as ISO/IEC 15444-2.

The block diagram of JPEG 2000 is shown in figure 5

Figure 5: Block diagram of JPEG 2000[21]

Quantization: Each subband may use a different step-size. Quantization can be skipped to

achieve lossless coding

• Entropy coding: Bit plane coding is used, the most significant bit plane is coded first.

• Quality scalability is achieved by decoding only partial bit planes, starting from the MSB. Skippingone bit plane while decoding = Increasing quantization stepsize by a factor of2. [21]

As seen in figure 6, it is a PNG image showing comparison of compression techniques for images.

The first one is uncompressed, 378 kilo bytes. Second one is JPEG JFIF and third one is JPEG2000 both 11.2 kilo bytes.

Figure 6: Comparison of JPEG2000 with JPEG [23]

  1. JPIP

JPIP(JPEG 2000 Interactive Protocol) [22] is a compression streamlining protocol that works withJPEG 2000to produce an image using the least bandwidth required. It can be very useful for medical andenvironmentalawareness purposes, among others, and many implementations of it are currently being produced, including theHiRISEcamera's pictures, among others.[24]

JPIP has the capacity to download only the requested part of a picture, saving bandwidth, computer processing on both ends, and time. It allows for the relatively quick viewing of a large image in low resolution, as well as a higher resolution part of the same image. Using JPIP, it is possible to view large images (1Gigapixel) on relatively light weight hardware.

Non-diagnostic imaging

Neuro-imaginghas also been used in experimental circumstances to allow people (especially disabled persons) to control outside devices, acting as abrain computer interface. [25]

Neuro-imaging falls into two broad categories:

  • Structural imaging, whichdealswith the structure of the brain and the diagnosis of gross (large scale) intracranial disease (such as tumor), and injury, and
  • functional imaging, which is used to diagnose metabolic diseases and lesions on a finer scale (such asAlzheimer's disease) and also for neurological andcognitive psychologyresearch and buildingbrain-computer interfaces.

Functional imaging enables, for example, the processing of information by centers in the brain to be visualized directly. Such processing causes the involved area of the brain to increase metabolism and "light up" on the scan. See figure 7, it is a 3D MRI scan of a semiconscious brain.

Figure 7: 3D MRI section of the head [25]

Proposed Work

This project introduces the concept of medical imaging and divulges into its technologies like MRI, tomography, ultrasound etc. It will also compare the compression techniques of medical imaging i.e. JPEG2000 and JPIP on the basis of their bit rates, SSIM index [28], and complexity.

This project proposes to demonstrate creation of 3D images of CT/MRI scan from a normal 2D image. It also shows some circumstances of neuroimagingi.e non-diagnostic medical imaging as in Figure 6.

References

  1. G. Mitchell. andG. Morgan-Hughes; "Radiation-reduction strategies in cardiac computed tomographic angiography"; Clinical Radiology Volume 65, Issue 11, pp. 859–867Roobottom CA, November 2010
  2. S. Vedanthamand A. Karellas;"Modelling the performance characteristics of Computed Radiography (CR) systems"; IEEE Trans. Medical imaging, Volume 29, Issue 3 pp. 790-806; March 2010
  3. L.F. Squire and R.A. Novelline ;Squire's fundamentals of radiology(5th ed.).Harvard University Press.ISBN0-674-83339-2; 1997
  4. B. J. Erickson and C.R. Jack Jr.;"Correlation of single photon emission CT with MR image data using fiduciary markers", .American Journal of Neuroradiology, Vol. 14, Issue 3 pp.713-720; October 2011
  5. A. Mulloni, D. Wagner , I. Barakonyi andD. Schmalsteing; Graz Univ of Technology- Indoor positioning and navigation with camera phones; Graz- April 2009
  6. M. Xu and L.H. Wang. "Photoacoustic imaging in biomedicine",Review of Scientific Instruments,77(4): 041101.doi:10.1063/1.2195024; 2006
  7. “Computed tomography—Definition from the Merriam-Webster Online Dictionary"Retrieved 2009-08-18.
  8. G.T. Herman, Fundamentals of computerized tomography: Image reconstruction from projection, 2nd edition, Springer, 2009
  9. S. Richard and C. Cobbold,Foundations of Biomedical Ultrasound, Oxford University press; pp. 422–423. 978-0-19-516831-0, 2002
  10. A. Yamani; A novel pulse-echo technique for medical three dimensional imaging;IEEE Trans Medicalimaging; Volume 16 Issue 6 pp. 938-942; Dec 1997
  11. Chris C. Shaw-Dimensions in medical imaging: the more the better?Proceedings of the IEEE, Vol. 98. No.1 pp. 1-4, January 2012
  12. K.R.Rao and Y. Huh; Video/Image processing and multimedia communications 4th EURASIP-IEEE Region 8 International symposium, JPEG 2000- USA-2002
  13. eeweb.poly.edu/~yao/EE3414/JPEG.pdf
  14. A. Khademi and A.Krishnan;"Comparison of JPEG 2000 and other lossless compression schemes" ; Paper in Engineering in medicine and biology society conference (IEEE EMBS), 2005
  15. (Figure 5)
  16. Microsoft and NASA Bring Mars Down to Earth Through the WorldWide Telescope (07.12.10) - NASA
  17. A.G.Filler ;"The history, development, and impact of computed imaging in neurological diagnosis and neurosurgery" CT, MRI, DTI:Nature Proceeding DOI: 10.1038/npre.2009.3267.5.Neurosurgical Focus (in press); 2009
  18. (Figure 6)
  19. Picture reference: sbharris on wikipedia