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2. BASIS OF DIAGNOSTIC RADIOLOGY
Various anatomical structures of the body have different densities for the X-rays.
When X-rays from a point source penetrate a section of the body, the internal body structures absorb
varying amounts of the radiation. ex
The main properties of X-rays, which make them suitable for the purposes of medical diagnosis,
are;-
1. Capability to penetrate matter coupled with differential absorption observed in various materials
2. Ability to produce luminescence and its effect on photographic emulsions.
The X-ray picture is called a radiograph, which is a shadow picture produced by X-rays emanating
from a point source and usually obtained on photographic film
The skeletal structures are easy to visualize and even the untrained eye can sometimes observe
fractures and other bone abnormalities. but
3. 1. Chest radiographs are mainly taken for examination of the lungs and the heart. Because of the air
enclosed in the respiratory tract, the larger bronchi are seen as a negative contrast, and the pulmonary
vessels are seen as a positive contrast against the air-filled lung tissue.
2. Heart examinations are performed by taking frontal and lateral films.
The evaluation is performed partly by calculating the total heart volume and partly on the basis of any changes
in shape.
For visualization of the rest of the circulatory system and for the special examinations of the heart, use is made
of injectible, water-soluble organic compounds of iodine.
A contrast medium is injected into an artery or vein, usually through a catheter placed in the vessel.
Therefore, all the larger organs of the body can be examined by visualizing the associated vessels and this
technique is called angiography. The examination is designated according to the organ examined—
e.g. for coronary angiography—the coronary vessels of the heart, angiocardiography—the heart, and
cerebral angiography— the brain.
4. Cont....
The entire gastro-intestinal tract can be imaged by using an emulsion of barium sulphate as a
contrast medium. It is swallowed or administered to diagnose common pathological conditions
such as ulcers, tumours or inflammatory conditions.
Negative and positive contrast media are used for visualizing the spinal canal, the examination being
known as myelography.
The central nervous system is usually examined by pneumography, i.e., filling the body cavities with
air. It may, however, be mentioned that computerized tomography has greatly reduced the need for
some of the invasive neuro-radiological methods, which involve discomfort and a certain risk for the
patient.
5. NATURE OF X-RAYS
X-rays are electromagnetic radiation located at the low wavelength end of the electromagnetic
spectrum. The X-rays in the medical diagnostic region have wavelength of the order of 10–10m.
They propagate with a speed of 3 ¥ 1010 cm/s and are unaffected by electric and magnetic
fields. According to the quantum theory, electromagnetic radiation consists of photons, which
are conceived as ‘packets’ of energy. Their interaction with matter involves an energy exchange
and the relation between the wavelength and the photon is given by
6. Image stabilization
In photography and videography, image stabilization is a technique or process used to stabilize
images and videos that occurs when the camera shakes because of unsteady hands.
Image resolution?
The details held by a particular image are known as image resolution. The higher the resolution, the
more visible the details are in an image. Image resolution quantifies how close lines can get to each
other while remaining visibly resolved.
What is image processing?
Image processing describes the process of digitally transforming an image and executing specific
operations to obtain useful information from it. Image processing systems often treat images as 2D
signals when applying some predetermined signal processing approaches.
7. Image Resolution
Image resolution is the details that an image can contain.
The details depend on the following factors:
1 - Contrast Resolution
2 - Spatial Resolution
Contrast Resolution:-
Contrast resolution in radiology refers to the ability of any imaging modality to distinguish between
differences in image intensity.
The inherent or identity contrast resolution of a digital image is given by the number of possible
pixel values,
In the case of digital imaging, it depends on the bit-depth of the system.and is defined as the number
of bits per pixel value.
An 8-bit system can show only 256 gray values instead
A 12-bit system, which shows 4096 gray values.
The 8-bit system shows fewer gray values and is a high contrast system than the 12-bit system,
which shows more gray values and is a low contrast system.
8. Cont.....
Spatial Resolution;-
Spatial resolution in radiology refers to the ability of an imaging system to differentiate between two
nearby objects.
In digital imaging, it depends on the size of the pixel used. A large pixel size will be unable to resolve
two nearby structures compared to small pixel size.
The measuring unit of spatial resolution is in line pairs per millimeter
A has a low spatial resolution, and B has a high spatial resolution.
9. Digital Images
• A digital image is a representation of a real image as a set of numbers that can be stored and
handled by a digital computer.
• to translate the image into numbers, it is divided into small areas called pixels (picture elements).
• For each pixel, the imaging device records a number, or a small set of numbers, that describe some
property of this pixel, such as its brightness (the intensity of the light) or its color.
• The numbers are arranged in an array of rows and columns that correspond to the vertical and
horizontal positions of the pixels in the image.
10. Digital images have several basic characteristics
1. Black and white image records only the intensity of the light falling on the pixels.
2. Color image , RGB (Red, Green, Blue) or four colors, CMYK (Cyan, Magenta, Yellow, blacK).
RGB images are usually used in computer monitors and scanners, while CMYK images are used
in color printers.
3. Non-optical images such as ultrasound or X-ray in which the intensity of sound or X-rays is
recorded. In range images, the distance of the pixel from the observer is recorded.
4. Resolution is expressed in the number of pixels per inch (ppi). A higher resolution gives a more
detailed image. A computer monitor typically has a resolution of 100 ppi, while a printer has a
resolution ranging from 300 ppi to more than 1440 ppi. This is why an image looks much better
in print than on a monitor.
11. Types Of Digital Images
1. Binary images
2. Gray-scale images
3. Color images
4. Multispectral images
12. Binary images
• Binary images can take one two value 0 and 1 or typically black and white. Binary images takes
only 1 binary digit to represent each pixel so it is also known as 1-bit image. e.g. – optical
character recognition (OCR).
• Through threshold operation from the gray-scale images binary images are created. In threshold
operation , every pixel above the threshold value is turned white (1), and those below the
threshold are turned black (0).
13. GRAY-SCALE IMAGE
These images are also known as monochrome or one-color images.
Gray-level images only contain gray level information they do not contain any color information.
Available number of different gray levels is determined by the number of bits used for each pixel.
For example: for 256 different gray level gray scale image should contain 8bits/pixel data.
12 or 16bits/pixel data are used for the medical imaging and astronomy.
14. COLOR IMAGES
Color images are created as three-band monochrome image data, in which each band of image data
corresponds to a different color. In each spectral band there is a gray-level information which is the
actual information stored in the digital image.
Color images are also known as the RGB image because color images are represented as the red,
green, and blue. Color images would have 24-bits/pixels by using 8-bit monochrome standard as a
model and 8-bits for each of the three color band (red, green and blue).
15. MULTISPECTRAL IMAGES
This type of images contain the information outside the normal human perceptual range. Information
represented is not directly visible by human system so, these are not images in the usual sense.
However by mapping the different spectral band to RGB components the information is represented
in visual form. Multispectral images include the ultraviolet, infrared, X-ray, radar data and acoustic.
16. IMAGE TRANSFORMATION
Image transformation is a function that produces an image as
output and takes an image as input. The input and output image
may have different interpretation or may appear entirely
different, depending on the transform chosen.
Example of image transformation are principal component
analysis, fourier transform and various spatial filter.
17. Image segmentation
Image segmentation is the process of
partitioning a digital image into multiple image
segments, also known as image regions or image
objects.
The goal of segmentation is to simplify an image
into something that is more meaningful and
easier to analyze.
Image segmentation is typically used to locate
objects and boundaries
Let’s understand image segmentation using a
simple example. Consider the below image:
There’s only one object here – a dog
18. Cont....
Now, there’s another animal/object in the image.Now Image localization comes into the picture
In case we have multiple objects present, then we need object detection (OD).
19. Uses of Image Segmentation
Cancer has long been a deadly illness. Even in today’s age of technological advancements, cancer can be
fatal if we don’t identify it at an early stage. Detecting cancerous cell(s) as quickly as possible can
potentially save millions of lives.
The shape of the cancerous cells plays a vital role in determining the severity of the cancer. You might have
put the pieces together – object detection will not be very useful here. We will only generate bounding
boxes which will not help us in identifying the shape of the cells.
Image Segmentation techniques make a MASSIVE impact here. They help us approach this problem in a
more granular manner and get more meaningful results.
20. The Electromagnetic Spectrum
Before we discuss to system and Modility wa have to know aboute (EMS)
EM spectrum is the range of frequencies of all types of EM radiation.
Radiation is energy that travels and spreads out as it goes – the visible light that comes
from a lamp in your house and the radio waves that come from a radio station are two
types of electromagnetic radiation.
The other types of EM radiation that make up the electromagnetic spectrum
are microwaves, infrared light, ultraviolet light, X-rays and gamma-rays.
Electromagnetic radiation can be described as particles, called photons, each traveling in
a wave-like pattern at the speed of light.
Each photon contains a certain amount of energy.
21. Cont....
The different types of radiation are defined by the the amount of energy found in the photons.
Radio waves have photons with low energies, microwave photons have a little more energy than
radio waves, infrared photons have still more, then visible, ultraviolet, X-rays, and, the most
energetic of all, gamma-rays.
22. Cont...
Radio:
Radio captures radio waves emitted by radio stations, bringing your favorite
tunes. Radio waves are also emitted by stars and gases in space.
Microwave:
Microwave radiation will cook your popcorn in just a few minutes, but is
also used by astronomers to learn about the structure of nearby galaxies.
Infrared:
Night vision goggles pick up the infrared light emitted by our skin and
objects with heat. In space, infrared light helps us map the dust between
stars.
23. • Visible:
Our eyes detect visible light. Fireflies, light bulbs, and stars all emit visible light.
• Ultraviolet:
Ultraviolet radiation is emitted by the Sun and are the reason skin tans and burns. "Hot" objects in
space emit UV radiation as well.
• X-ray:
A dentist uses X-rays to image your teeth, and airport security uses them to see through your bag. Hot
gases in the Universe also emit X-rays.
• Gamma ray:
Doctors use gamma-ray imaging to see inside your body. The biggest gamma-ray generator of all is
the Universe.
Cont...
24. Measuring electromagnetic radiation
Electromagnetic radiation can be expressed in terms of frequency, wavelength and energy
Frequency is measured in cycles per second, or Hertz (Hz)
Wavelength is measured in meters. (M)
Energy is measured in electron volts (eV) .
Each of these three quantities for describing EM radiation are related to each other .
Comparison of wavelength, frequency and energy for the electromagnetic spectrum.
25. Con....
Generally, scientists use whatever units are easiest for the type of EM radiation. Example,
Radio part of the EM spectrum falls in the range from about( 1 cm to 1 km), which is (30 GHz to
300 kHz in frequencies).
Infrared use microns (millionths of a meter) for wavelengths, so their part of the EM spectrum
falls in the range of (1 to 100 microns).
Blue, green, yellow, orange, and red light have wavelengths between (400 and 700 nanometers).
The wavelengths of ultraviolet, X-ray and gamma-ray of the EM spectrum are very small.
Instead of using wavelengths, usually measured in electron volts (eV) according to the energies
these photons have.
Ultraviolet radiation falls in the range from a few electron volts to about (100 eV).
X-ray photons have energies in the range (100 eV to 100 keV).
Gamma-rays photons have energies greater than 100 keV.
