X-Ray Technology

By: PROF. Dr. Moustafa Moustafa Mohamed

Faculty of Allied Medical SciencePharos University in Alexandria

Introduction to Medical Imaging

Uses of medical imaging Obtain information about internal bodyorgans or the skeleton to determine a patient’s physical

NON Invasive

Imaging Modalities: * X-ray (plan , Dental, Panorama, Mammo, Angio, …)

* C.T * Ultrasound

* MRI * Gamma Camera

* PET SPECT

Medical Image

• Generated by means of radiation– electromagnetic (EM)– ultrasound– electrons

• Displayed for interpretation on

– Film– photograph or – computer display monitor

Types of image

1) Projections

2) Dimensional

3D & 4D

3) Slices

• Trans axial - plane normal to a vector from head to toe. • Coronal - plane normal to a vector from front to back • Sagittal - plane normal to a vector from left to right. • Oblique - a slice that is not (at least approximately) one of the above.

The NUCLEUS is made upof PROTONS and NEUTRONS

PROTONS have a positive charge.

NEUTRONS have no electrical charge.

Inside the atomInside the atom

Inside the atomInside the atom

ELECTRONS have a negative charge.

The number of electrons in an atom usually matches the number of protons, making the atom electrical neutral.

Exactly what is an X – Ray?• An x – ray is a form of radiation, that is

invisible• Electromagnetic waves of short wavelength

with wavelengths between about 0.02 Å and 100 Å (1Å = 10 10‐ meters).

• Very high energy• Basically gives an “inside view”

• The energy of X rays, like all electromagnetic radiation, is inversely ‐proportional to their wavelength as given by the Einstein equation:

E = hν = hc/λ where E = energy h = Planck's constant, 6.62517 x 10 27‐ erg.sec ν = frequency c = velocity of light = 2.99793 x 1010 cm/sec λ = wavelengthSince X rays have a smaller wavelength than visible light, they have higher ‐

energy.

• X rays can penetrate matter more easily than can visible light.‐• Their ability to penetrate matter depends on the density of the matter• X rays provide a powerful tool in medicine for mapping internal structures ‐

of the human body (bones have higher density than tissue,• and thus are harder for X rays to penetrate, fractures in bones have a ‐

different density than the bone, thus fractures can be seen in X ray ‐pictures).

History

• In 1895 Wilhelm Roentgen, German Physicist, was studying high voltage discharges in vacuum tubes, then he noticed fluorescence of barium platinocyanide screen lying several feet from tube end.

• These rays where named– X-rays--invisible penetrating radiation,– X represent unknown in mathematics

William ConradRoentgen

• Wilhelm Conrad Rontgen Won the first Nobel Peace Prize for physics in 1901

                    

Early X- Ray Images

                                    In

                        Right: Mrs. Röntgen's hand, the first X-ray

X-ray of Bertha Roentgen'sHand

Types and uses of X-ray Types and uses of X-ray

Types and uses of X-ray

Diagnostic Therapeutic

Still picture Still picture scan tomographyContinuous picture

Various uses of the X - RayDetect malformations in bones

• Treats disorders such as various cancers• Security purposes• Alternatives for cancer detection• Annual physical exams• Pre-surgery evaluations

Electromagnetic Spectrum

Production of X-rays (1)

• X-rays are produced when rapidly moving electrons that have been accelerated through a potential difference of order 1 kV to 1 MV strikes a metal target.

Evacuatedglass tube

Target

Filament

Production of X-rays (2)

• Electrons from a hot element are accelerated onto a target anode.

• When the electrons are suddenly decelerated on impact, some of the kinetic energy is converted into EM energy, as X-rays.

• Less than 1 % of the energy supplied is converted into X-radiation during this process. The rest is converted into the internal energy of the target.

Properties of X-rays

• X-rays travel in straight lines.• X-rays cannot be deflected by electric field or

magnetic field.• X-rays have a high penetrating power.• Photographic film is blackened by X-rays.• Fluorescent materials glow when X-rays are

directed at them.• Photoelectric emission can be produced by X-rays.• Ionization of a gas results when an X-ray beam is

passed through it.

X-ray Spectra (1)

• Using crystal as a wavelength selector, the intensity of different wavelengths of X-rays can be measured.

X-ray Spectra (2)

• The graph shows the following features.– A continuous background of X-radiation in which the

intensity varies smoothly with wavelength. The background intensity reaches a maximum value as the wavelength increases, then the intensity falls at greater wavelengths.

– Minimum wavelength which depends on the tube voltage. The higher the voltage the smaller the value of the minimum wavelength.

– Sharp peaks of intensity occur at wavelengths unaffected by change of tube voltage.

Minimum wavelength in the X-ray Spectra

• When an electron hits the target its entire kinetic energy is converted into a photon.

• The work done on each electron when it is accelerated onto the anode is eV.

• Hence hf = eV and the maximum frequency

h

eVf max

Therefore,

eV

hcmin

Continuous (Bremsstrahlung) X-Ray Production

Characteristic X-ray Spectra

• Different target materials give different wavelengths for the peaks in the X-ray spectra.

• The peaks are due to electrons knock out inner-shell electrons from target atoms.

• When these inner-shell vacancies are refilled by free electrons, X-ray photons are emitted.

• The peaks for any target element define its characteristic X-ray spectrum.

Characteristic X-Ray Production

Anode Heating

• This occurs when projectile electrons excite an atoms outer shell electrons but do not eject them from the atom.

• For most X-ray machines, about 99% of the projectile electrons lose energy this way.

• Infrared EM radiation (observed as heat energy) is produced when the excited electrons relax and fall back into the original energy level

• The amount of anode heating can be reduced by increasing the energy of the projectile electrons so that they cause more ionization rather than excitation.

Uses of X-rays

• In medicine To diagnose illness and for

treatment.• In industry

To locate cracks in metals.• X-ray crystallography

To explore the structure of materials.

Conditions for x ray production

• Separation of electrons• Production of high speed electrons• Focusing of electrons• Sopping of high speed electrons in target

COLD GAS CATHODE TUBE

• glass tube with partial vacuum with small amount of gas,

• two electrodes, one negative (cathode)• & another positive (Anode).

Hot Cathode Diode tube• In 1913 W.D. Coolidge invented new type of

tube on Edison principal called• Hot Cathode Diode tube.• It made possible the control of mA and kV

independently and there by controlling the quantity and quality of x-rays.

PARTS OF X RAY TUBE

• Glass Tube• Cathode

– Filament– Supporting wires– Focusing cup

• Anode– Stationary– Rotating

•·        X-ray tube

•·        X-ray electrical power generator

•·        Control unit

•·        Film or digital system

In addition to:

•·        Table unit

•·        Bucky film tray and grid system

•·        Suspension system

Main components of x-ray unit are:

Introduction

X-ray image is a shadow picture produced by x-rays emitted from a point source

Image contrast is (((proportion with)))

1- Mass attenuation coefficient of the imaged part

2- Density3- Thickness

Battery

Principles of X-ray tubePrinciples of X-ray tube

Main components of a modern x-ray tube

• A heated filament releases electrons that are accelerated across a high voltage onto a target.

• The stream of accelerated electrons is referred to as the tube current.

• X rays are produced as the electrons interact in the target. • The x rays emerge from the target in all directions but are restricted

by collimators to form a useful beam of x rays. • A vacuum is maintained inside the glass envelope of the x-ray tube

to prevent the electrons from interacting with gas molecules.

X-Ray Tubes

X ray Absorption‐• When the x rays hit a sample, the oscillating electric field of the ‐

electromagnetic radiation interacts with the electrons bound in an atom.• Either the radiation will be scattered by these electrons, or absorbed and

excite the electrons.• A narrow parallel monochromatic x ray beam of intensity ‐ I0 passing

through a sample of thickness x will get a reduced intensity I according to the expression:

• I = I0 e‐μ x or Ln (I0 /I) = μ x

• where μ is the linear absorption coefficient, which depends on the types of atoms and the density ρ of the material.

How X ray Lose Energy within ‐Matter?

• • Photoelectric effect• X ray interacts with an electron by giving all ‐

its energy to the electron near the nucleus.• It is the most probable way of losing energy• X ray energy must be greater than or equal to ‐

the electron binding energy to the nucleus

• Compton effect

• X ray (of energy at least 511 KeV) ‐colloids with a loosely bound outer electron.

• The electron receive part of the energy and the rest goes in different direction as a scattered photon radiations each of 511 KeV

Pair production

• X ray (of energy at least 1.02 MeV) ‐penetrates the intense electric field of nucleus. It is converted to an electron and a positron each of 511 KeV.

• The positron will then colloids with one electron and results in the production of two annihilation

Bragg's Law

• According to Bragg, X ray diffraction can be viewed as a process similar to ‐reflection from planes of atoms in the crystal.

• In Bragg's construct, the planes in the crystal are exposed to a radiation source at a glancing angle θ and X rays are scattered with an angle of reflection also equal to θ. The incident and diffracted rays are in the same plane as the normal to the crystal planes.

• Bragg reasoned that constructive interference would occur only when the path length difference between rays scattered from parallel crystal planes would be an integral number of wavelengths of the radiation.

• When the crystal planes are separated by a distance d, the path length difference would be 2d sin θ. Thus, for constructive interference to occur Bragg’s law must be fulfilled.

• For constructive interference: nλ = 2a• From trigonometry: a = d sin θ• or 2a = 2 d sin θ• thus, nλ = 2d sin θ• What it says is that if we know the wavelength ,λ , of the X rays going in ‐

to the crystal, and we can measure the angle θ of the diffracted X rays ‐coming out of the crystal, then we know the spacing (referred to as d‐spacing) between the atomic planes.

d = nλ /2 sin θ

Checkpoint Question 1What are x-rays?

• X-rays are high-energy waves that travel at the speed of light. X-rays can penetrate fairly dense objects, such as the human body. They cannot be seen, heard, felt, tasted, or smelled.

Checkpoint Question 2• Why is it important to schedule a barium

enema before an upper GI or barium swallow?

Answer• Barium enemas involve filling only the large intestine

with barium. Because the large intestine is the last part of the GI tract, this barium can be eliminated more quickly. If an upper GI examination is performed first, it may be days later before barium can be eliminated, thus delaying other examinations.

Radiation Safety• X-rays have potential to cause cellular or

genetic damage• At highest risk

– Pregnant women– Children– Reproductive organs of adults

Radiation Safety Proceduresfor Patients

1. Reduce exposure amounts as much as possible

2. Avoid unnecessary examinations3. Limit area of body exposed4. Shield sensitive body parts5. Evaluate potential pregnancy status

Radiation Safety Proceduresfor Clinical Staff

1. Limit amount of time exposed to x-rays2. Stay far away from x-rays3. Use available shielding4. Avoid holding patients during exposure5. Wear individual dosimeters6. Ensure proper working condition of equipment

Diagnostic Procedures

• Routine radiographic examinations • Named for part of body involved• Performed for viewing bone structure or

abnormalities

Mammography

• Specialized x-ray examination of the breast• Screening tool for breast cancer• Breast compressed in specialized device• Has become vital adjunct to biopsy

procedures

Contrast Media Examinations

• Radiographic contrast media helps differentiate between body structures

• Used to evaluate structure and function

Contrast Media

• Introduced into body in several ways– Swallowing– Intravenously– Through a catheter

• Medical assistant must ensure that patients understand preparation instructions

Checkpoint Question 3

• How do contrast media help in differentiating between body structures?

Answer

• Contrast media help differentiate between body structures by artificially changing the absorption rate of a particular structure so that it can be seen clearly instead of blending in with adjacent structures. For example, barium sulfate absorbs radiation and shows up as white areas on a radiograph.

Fluoroscopy

• Use x-rays to observe movement within the body– Barium sulfate through the digestive tract– Iodinated compounds showing the beating of the

heart

Computed Tomography (CT, CAT scan)

• Tomography– X-ray tube and film move in relation to one

another, blurring all structures except those in focal plane.

• CT uses x-rays from a tube circling the patient, analyzed by computers to create cross-sectional images

Checkpoint Question 4

• How does fluoroscopy differ from computed tomography and sonography?

Answer

• Fluoroscopy uses x-rays to show movement within the body. CT uses a combination of x-rays and computers to create cross-sectional images of the body. Sonography uses high-frequency sound waves to create cross-sectional still or real-time (motion) images of the body.

Radiation Therapy

• High-energy radiation is used to destroy cancer cells

• Treatments must be planned carefully by radiologist

• Most patients have some side effects

Transfer of Radiographic Information

• Radiographic images remain part of permanent record

• Digital images saved on disk• X-ray films belong to site where study was

performed• Examining physician or radiologist writes summary

of the examination• Medical assistant obtains patient’s permission to

have summary sent to office physician

Teleradiology

• Use of computed imaging and information systems

• Provides new benefits in medicine• Digital images can be transmitted via

telephone lines to distant locations• Allows for consultation with experts on

difficult cases

Dental X- Rays • What is the purpose of dental x- rays• What does the assistant giving the x- ray look

for• What is the educational requirements of the

person giving the x- ray• Specific shots that are taken when in the

“chair”

Purpose of dental x - raysPurpose of dental x - rays

• To help the dentist reach a correct To help the dentist reach a correct diagnosis.diagnosis.

• Help to provide the patient with Help to provide the patient with proper care and treatment.proper care and treatment.

What is found through x – rays?• Tooth Decay• Periodontal disease• Extra Teeth• Bone cancer (cysts)• Osteoporosis• Root fragments( configuration)• Abscesses of the teeth or gums• Tooth position• Tatar below the gum line• Jaw joint irregularities• Facial bone composition

Reported problems

• Table systems - mechanical system for positioning tabletops -Wires and cables may break ---- tabletop to jam

• Control unit-Control levers jam (MA, KV, Time, …)

• Collimator (Levers)• Light Localizer• Tube• PCB Control• Mechanical jam of film tray• Collimator loss from its x-ray tube

****** LOSS X-RAY TUBE SUSPENSION ******

Purchase Considerations

Tube(focal spot of the tube determine the resolution of images)

Generator(High frequency generator needs less space and smaller HV cables)

Table(Fixed, floating top, tilting, or elevating which is suitable fortraumatic and emergency patients).

Digital radiography Image quality, storage space,Digital Imaging and Communication in Medicine (DICOM),remote control,