Medical Imaging

Medical imaging
Medical imaging is the visualization of the interior of a body. It is the technique and process which seeks to reveal internal structures hidden by the skin and bones for clinical diagnosis, treatment and disease monitoring. There are many types of medical imaging, the main types of imaging used in modern medicine are radiography, magnetic resonance imaging (MRI), nuclear medicine imaging(such as PET and SPECT), and ultrasound.

Radiography
Radiography uses electromagnetic radiation in X-ray range (ionizing radiation) to take images of the internal parts of the body by sending beams through the body. The X-rays are absorbed by the material they pass through in differing amounts depending on the density and composition of the material (soft tissues do not absorb these rays while objects such as bones do).

Computed Tomography
Computed Tomography (CT) is an imaging technique that combines a series of X-ray images taken from different angles to create cross-sectional internal images, resulting in more detailed images compared to regular X-rays.

Magnetic Resonance Imaging
Magnetic Resonance Imaging (MRI) involves radio waves and magnetic fields to look at the internal structures of the body. The MRI scanner uses powerful magnets to polarize and excite hydrogen nuclei of water molecules in human tissue, producing a detectable signal resulting in images of the body.

Nuclear Medicine Scan
Nuclear Medicine Scan (such as PET and SPECT) involves in the use of radioactive tracers, which are radioactive materials that are injected or swallowed to travel through the digestive or the circulatory system. The radiation produced by the material can then be detected by the use of a special camera (e.g. gamma camera) to take pictures of tissues and organs in the body to observe its activity and function.

Ultrasound Imaging
Ultrasound Imaging uses high frequency sound waves which are reflected off body tissue to create images of organs, muscles, joints, and other soft tissues. The light travels through the skin layers which can be viewed by using electronic sensors.

Digital Image
A digital image is a numeric representation of a two-dimensional image. Depending on whether the image resolution is fixed, it may be of vector or raster type. By itself, the term "digital image" usually refers to raster images or bitmapped images. Digital images (raster images or bitmapped images) are made of picture elements called Pixels.

Resolution and size of the image
Pixels are organized in an ordered rectangular array. The sesolutionize of an image is determined by the dimensions of this pixel array: The image width is the number of columns, and the image height is the number of rows in the array.

Each pixel can contain a color value. It is called a color depth. It can contain only basic colours or shades of gray which can be typically sufficiently saved in 8 bits. However the true colour images need 24 bits or more. The size of the image in(e.g. in MB) is then given by: resolution of the image times bits for the pixel (color depth)

Image Digitization
Digitization is the process used to convert analogue data (such as text, image) into digital form that is saved in the computer memory, through two steps:

1. Sampling
Analog signal is read at specific sampling frequency to create sample of analog signal at each specific point. The frequency of sampling is referred to as resolution of the image, and sampling turns continuous data (analog) into discrete (digital) data.

2. Quantization
Each sample (pixel) is quantified. That means that a numerical value is assigned to each pixel (such as 0-255 in the case of an 8-bit grayscale image). By the quantization activity of Digitization, the brightness levels are determined.

Image Contrast
Contrast can be defined as the differences in intensities of colors between the pixels in an image. If the differences in intensities are high then that translates to an image having a high contrast, but if the differences in intensities were low then the image would have a low contrast.

Function
After getting a digital image, the next step is its evaluation.

In medical imaging this is of particular relevance, because we don’t need an aesthetic but a highly detailed image to base diagnoses on.

An easy way to visualize the quality of greyscale pictures are histograms. The histogram is a graph showing the number of pixels in an image that refers to each different pixel intensity value (how often it appears).

Applications
•	Image processing

•	Brightness adjustments

•	Equalization of an image

•	Thresholding (minarization of image - results in two colours only - black/white)

Image Formats
Some of the more common examples of digital image formats are '''JPEG, TIFF, and PNG. '''JPEG Supports the 8-bit grayscale and 24-bit color images. TIFF is an adaptable file format that can save 8 or 16-bits per color for 24 and 48-bit totals. PNG which supports 8-bit paletted images and 24 and 48-bit TrueColor.

Compression
Most of the Digital Image Formats can be divided by their compression method:

Loseless
No information is lost from the digital image file when a compression algorithm is applied to it. Includes: RAW, TIFF, PNG and BMP. Those image formats store the full RGB digital image without any loss of information. This comes with the advantage of permitting high quality reproductions but at the price of requiring a lot of memory to save those files.

Lossy
Results in the loss of some image data to achieve a smaller file size. Includes: JPEG, GIF. JPEG achieves compression by removing some color and image details. GIF compression is achieved by limiting the total number of colors allowed to be present in the image file.

DICOM
Digital imaging and Communication in Medicine, also known as DICOM, is used in medical purposes to store, share and handle information of imaging files. It enables integration of different medical devices, such as scanners, servers and workstations, from multiple manufacturers by using the communication protocol TCP/IP.

PACS
working alongside DICOM are picture archive and communication systems, or PACS, which is capable of storing 2D and 3D medical images. This system allows professionals to save and handle the large database of MRI, CT scan, X-rays and other paperless radiology or to send it to other doctors in hospital.