ELECTRICAL ENGINEERING DEPARTMENTSpring 2012

EE 5359-002 (DE) – Multimedia ProcessingProject Report On

MEDICAL IMAGING

GUIDED BY: DR. K.R.RAO

SUBMITTED BY:

Anuja Kulkarni (1000722132)

MEDICAL IMAGING

ABSTRACT

Medical imaging[1] as the name suggests is the technique and process used to create images of parts and functions of human body for clinical purposes. It is a medical procedure seeking to reveal, diagnose or examine disease.

As a discipline, it is part of biological imaging and incorporates radiology, nuclear medicine, investigative radiological sciences, endoscopy, (medical) thermography, medical photography and microscopy (e.g. for human pathological investigations). As a field of scientific investigation, medical imaging constitutes a sub-discipline of biomedical engineering, medical physics or medicine depending 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 TomographyCT - Computed TomographyDICOM - Digital Imaging and Communications in MedicineEEG - ElectroencephalographyEKG - ElectrocardiographyfMRI- Functional Magnetic resource imagingJFIF- JPEG File Interchange FormatJPIP- JPEG 2000 Interactive ProtocolMEG - MagnetoencephalographyMRI - Magnetic Resonance ImagingNMR- Nuclear Magnetic ResonanceRF- Radio Frequency

IntroductionMedical imaging [1]is the technique and process used to create images of the human body for clinical purposes. Although imaging of removed organs and tissues can be performed for medical reasons, such procedures are not usually referred to as medical imaging, but rather are a part of pathology.

As a discipline and in its widest sense, it is part of biological imaging and incorporates radiology, nuclear medicine, investigative radiological sciences, endoscopy, medical photography and microscopy.

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

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

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.

Up until 2010, 5 billion medical imaging studies have 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, they are-

1. Invisible light medical imaging2. Visible light medical imaging

In the clinical context, "invisible light" medical imaging is generally equated to radiology or "clinical imaging" and the medical practitioner responsible for interpreting the images is a radiologist.

"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. Diagnostic radiography designates the technical aspects of medical imaging and in particular the acquisition of medical images. The radiographer or radiologic technologist is usually responsible for acquiring medical images of diagnostic quality, although some radiological interventions are performed by radiologists. While radiology is an evaluation of anatomy, nuclear medicine provides functional assessment.

As a field of scientific investigation, medical imaging constitutes a sub-discipline of biomedical engineering, medical physics or medicine depending on the context: Research and development in the area of instrumentation, image acquisition (e.g. radiography), modelling and quantification are usually the preserve of biomedical engineering, medical physics and computer science; Research into the application and interpretation of medical images is usually the preserve of radiology and the medical sub-discipline relevant to medical condition or area of medical science i.e neuroscience, 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 of mathematical inverse problems. This means that cause is inferred from effect. In the case of ultra sonography the probe consists of ultrasonic pressure waves and echoes inside the tissue show the internal structure. In the case of projection radiography, the probe is X-ray radiation which 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 following medical imaging modalities do not penetrate the skin physically. But on the electromagnetic and radiation level, 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]

Fluoroscopy produces real-time images of internal structures of the body in a similar fashion to radiography, 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]

2. Magnetic Resonance Imaging (MRI)

A magnetic resonance imaging instrument [8] (MRI scanner), or "nuclear magnetic resonance (NMR) imaging" scanner as it was originally known, uses powerful magnets to polarise and excite hydrogen nuclei (single proton) 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.

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

Figure 2 shows a fMRI scan showing regions of activation in orange, including the primary visual cortex

Figure 2: A fMRI scan [9]

3. 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 from positron emission tomography can be related to anatomical information provided by magnetic resonance imaging (MRI). Similarly, fiducial points established during MRI can be correlated with brain images generated by magnetoencephalography to 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: Fiducial marker 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 Photo acoustic imaging [13] is a recently developed hybrid biomedical imaging modality based on the photo acoustic 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 photo acoustic imaging can be used in vivo for tumor angiogenesis monitoring, blood oxygenation mapping, functional brain imaging, and skin melanoma detection, etc.

5. Tomography [14]

Tomography is the method of imaging a single plane, or slice, of an object resulting in a tomogram. There are several forms of tomography like Linear tomography Poly tomography Zonography Orthopantomography Computed tomography [15]

X-ray computed tomography, also computed tomography (CT) or computed axial tomography (CAT), can be used for medical imaging and industrial imaging methods employing tomography created by computer processing. Digital geometry processing is used to generate a three-dimensional image of the inside of an object from a large series of two-dimensional X-ray images taken around a single axis 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 computer tomography of human brain, from base of the skull to top, taken with intravenous contrast medium.

Figure 4: Computed tomography of brain [16]

6. Ultrasound [17]

Medical ultra-sonography uses high frequency broadband sound waves in the mega Hertz range 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 an ultrasound 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

o A-scano B-scano Corneal topographyo Optical coherence tomographyo 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 2000 is the state-of-the-art image compression DICOM standard 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, called JPIP, to enable efficient streaming of the JPEG 2000 compressed image data.[1]

1. JPEG2000JPEG 2000 is an image compression standard and coding system. It was created by the joint photographic experts group committee in 2000 with the intention of superseding their original discrete cosine transform-based JPEG standard (created in 1992) with a newly designed, wavelet-based method. [20]

The standardized filename extension is .jp2 for ISO/IEC 15444-1 conforming files and .jpx for 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 toachieve 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. Skipping one bit plane while decoding = Increasing quantization stepsize by a factor of 2. [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]

2. JPIP

JPIP (JPEG 2000 Interactive Protocol) [22] is a compression streamlining protocol that works with JPEG 2000 to produce an image using the least bandwidth required. It can be very useful for medical and environmental awareness purposes, among others, and many implementations of it are currently being produced, including the HiRISE camera'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 imagingNeuro-imaging has also been used in experimental circumstances to allow people (especially disabled persons) to control outside devices, acting as a brain computer interface. [25]

Neuro-imaging falls into two broad categories:

Structural imaging, which deals with 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 as Alzheimer's disease) and also for neurological and cognitive psychology research and building brain-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, 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 neuroimaging i.e non-diagnostic medical imaging as in Figure 6.

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