MEDICAL IMAGING : AN INTRODUCTION

Medical imaging is a field that grows constantly along with the other disciplines of healthcare area at present. It promises better healthcare by helping in diagnosing the complex diseases at an early stage. Medical imaging deals with different imaging methods and image processing that enhances the quality of imaging and thus in diagnosing. Therefore it is quite worthy for a biomedical engineer to have a concrete knowledge in this arena.


Image processing is similar to signal processing, just that image has multiple dimensions. Signals are one dimensional, f(t) which is represented by amplitude and time whereas in case of images are two dimensional, f(x,y) is represented using amplitude of intensity and x, y coordinates as pixels. The size and number of pixels determine the quality of image. The need of image processing is when the images taken are to be transferred especially in case of space- craft photographs. These photographs when transferred included noise, to avoid the noise, processing is required. Also, in the reconstruction of images in medical field using different imaging techniques including CT, MRI, and Ultrasound etc. In industries, the image for error detection in manufacturing process of items also requires processing. The preprocessing includes converting the analog image or signal into discrete time signals then after quantizing these; we get a digital image or signal. Thus through different medical imaging techniques we can improve the quality of an image, which is of greater significance in medical, more precisely when the diagnosing field is concerned.

Medical Imaging is done in order to obtain the detailed view of the various body parts or body as a whole. Sophisticated technologies are used nowadays so as to perform the process with minimum harm and pain to the body. This is done via various methods which include radiology (which consists of X-Ray, PET, CT, MRI) endoscopy, etc. The image is reconstructed with the necessary enhancements, focussing on the desired part. This has helped doctors in diagnosing the disease condition in the earlier stages and providing necessary cure. After the discovery of X-Ray imaging the medical images play an important role in diagnostics, treatment planning and procedures, and further studies. Also these images are used for education, documentation and research in the morphology, the physical and biological functions in 1D, 2D, 3D and 4D images. Medical images contain noise due to interferences, nature of physiological system, and the imaging procedures add to distortion and attenuation of image thus diminishing the contrast and visibility. The difference between normal and abnormal tissues is very small which is confounded by these noise; hence becomes difficult to analyse acquired images.


The major areas covered in image processing are formation, visualisation, analysis and management. Image enhancement is done at pre- and post- stages of various processing steps with the help of algorithms. Image formation deals with steps from image capture to the image matrix formation. Image visualisation refers the manipulation of this matrix, and the optimized image output. Image analysis includes the processing of images in quantitative measurements and interpretations of medical images which requires a prior knowledge of nature and content of images. The core steps incorporates feature extraction, segmentation, classification, quantitative measurements, and interpretation. The feature extraction enhances the information contained in image for a particular amount and suppresses other levels of information.


In segmentation the image is divided into connected regions also the regions to be emphasised are determined by pre-stage of classification. Classification as the name implies classify the regions segmented above into various classes of object. The automatic detection of objects and their properties are determined through quantitative measurements and interpretation of images deals with analyzing the individual images in space or time domain. Image management deals with the storage, communication, transmission, archiving, and retrieval of image.