specialized imaging techniques using x-rays (1)

8/7/2019 Specialized Imaging Techniques Using X-rays (1)

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By

Deepashree D


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INTRODUCTION

RADIOGRAPHY

FLUOROSCOPY

ANGIOGRAPHY

MAMMOGRAPHY

COMPUTED TOMOGRAPHY

CONCLUSION


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Medical imaging is the process by which

physicians evaluate an area of the subject's

body that is not normally visible.

This process could be clinical or research

motivated and can also have scientific and

industrial applications.


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X-rays can be described in 2 ways1. Electromagnetic wave withv= f *=

wavelengthf = frequency andV=velocity

2. Particle or photon with Energyproportional to frequencyE = h * fh = Planck's constant = (4.13 e-18) [KeVsec]1 eV= 1.6 e-19 [Joule]


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Electromagnetic (EM)Spectrum


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X-ray Radiography

Fluoroscopy

Angiography

Subtraction & DSAMammography

CT


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Radiography is the creation of radiographs, photographs madeby exposing a photographic film or other image receptor toX-rays.

Since X-rays penetrate solid objects, but are slightlyattenuated by them, the picture resulting from the exposurereveals the internal structure of the object.

The most common use of radiography is in the medical field

(where it is known as medical imaging).


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X-ray radiography remains the most commonly used clinicalprocedure today.

The rays produced by the generator are filtered .

Immediately behind the patient are positioned the grid for removingthe scattered radiation and the screen-film combination for recordingthe image, which is a map of the transmitted X ray intensity .

X ray attenuation in a tissue is proportional to mass density of thetissue, the Xray intensity that has traversed a region of lower densitywill be greater than that which has traversed a region of higher density.

Lower density region is darker


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Conventional X-ray Radiography


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Digital X-ray image acquisition systems for

DigitalRadiography.


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DIGITALRADIOGRAPH


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Fluoroscopy is an imaging technique

commonly used by physicians to obtain real-

time images of the internal structures of a

patient through the use of a fluoroscope.

In its simplest form, a fluoroscope consists of an

x-ray source and fluorescent screen(Calcium

Tungstate) between which a patient is placed .


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Modern fluoroscopes couple the screen to an x-ray imageintensifierand CCD video camera allowing the images to belayed and recorded on a monitor.

In a typical fluoroscopic procedure for examining the digestive

tract, a contrast medium like barium sulphate that is nontoxicis either taken orally by the patient or by enema depending onwhich part of the GI tract is being examined.

The radiation dose received by the patient can be very high.

camera enabled viewing of the image on a monitor, allowing aradiologist to view the images in a separate room away fromthe risk ofradiation exposure


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FLUOROSCOPY


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The X ray image captured directly by an image intensifier as

in Fluoroscopy, and the image on the o/p screen of the image

intensifier is focussed and scanned by a video camera.

The video signal from the camera is digitized. The centre of

the system is a computer that controls the firing of the X ray

tube, imaging acquisition via the camera, and imaging

processing such as subtraction.


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Remains the golden standard for diagnosing a no. of clinical

disorders. (Coronary stenosis, Pancreatic disease, venousthrombosis,etc.

is a procedure involving radiographic visualization of blood vesselsby injecting a nontoxic substance such as water soluble organiccompounds of iodine into the blood stream.

Useful for demonstrating vessel constrictions and vascular tumors.

A bolus of contrast medium is injected into the artery or vein,usually through catheterization.

The medium is then rapidly diluted in the blood circulation.

A series of images are taken immediately after the injection.


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Angiography System


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Angiograms of cerebral circulationAngiograms of cerebral circulation


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Angiographic Imaging:

Blood vesselsinkidney.


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Is a procedure that is used to suppress background information

on an image and enhance the image of the object of interest.

Here the image before the injection of a contrast medium is

subtracted from the image obtained shortly following the

injection.

Disadv: The patient has to be motionless between exposures .


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DSAExampleDSAExample


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The same procedure performed digitally.

The components of a DSA system are similar to those of adigital fluoroscopy system with the exception that the video

signal from the video camera is typically logarithmicallyamplified before digitizing.

Allows signal processing algorithms such as contrastenhancement through windowing and filtering.


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Advantages

Better signal to noise ratio, larger signal amplification.better sensitivity.the injection can be performed with a smaller catheter,lessening the risk associated with puncturing an artery.DSA may be performed as an outpatient procedure.

The problem caused by patient motion is reduced.It is less costly .speed and efficiency.

Disadvantages:

It suffers from poorer resolutionsmaller field of view .not possible to produce multiple views simultaneously.


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It is the radiographic examination of the breast performedwith or without the injection of contrast medium.

The requirements for mammography are different from

ordinary X ray examination in the following reasons:i)Low energy X rays in the order of 20keV.

ii)Needs spatial resolution better than 0.1mm

iii)Exposure time should be short to avoid artifact due topatient motion.


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MAMMOGRAMMAMMOGRAM


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A mammography unit


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(CT), also known as computed axial tomography or

computer-assisted tomography (CAT) and body section

roentgenography, is medical imaging method employing

tomography where digital processing is used to generate

a three-dimensional image of the internals of an objectfrom a large series of two-dimensional X-ray images

taken around a single axis of rotation.

The word "tomography" is derived from the Greek tomos(slice) and graphia (describing).


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It is based on the principle that an image of an unknown objectcan be obtained if one has an infinite number of projectionsthrough the object.

X-ray slice data is generated using an X-ray source that rotates

around the object;

X-ray sensors are positioned on the opposite side of the circlefrom the X-ray source.

Many data scans are progressively taken as the object isgradually passed through the gantry.

They are combined together by the mathematical procedure

known as tomographic reconstruction.


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Patient

Detector

system

X-ray tube

Ray Beam

Computer

Principle of CTPrinciple of CT


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Schematic RepresentationSchematic Representation


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Principle of CT ContPrinciple of CT Cont


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11ststGENERATIONGENERATION 22ndnd GENERATIONGENERATION

33rdrd GENERATIONGENERATION 44thth GENERATIONGENERATION


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CT ScannerCT Scanner


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CT SCANNER ContCT SCANNER Cont


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Normal CT scan of the head Chest CT horizontal section

Computed Tomography contd


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With the discovery of X- rays we are able to learn more about

ourselves by looking within.

Medical Imaging by X-rays clearly illustrates the impact of

radiology on our everyday lives.

It is a great tool in medical field when strict protocol of its use

is applied not only because it has several invaluable potential

advantages but also its technology has been improving andmany ancillary appealing features, along with its core

development, are under intense investigations.


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specialized imaging techniques using x-rays (1)

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