DR.VISHNU MOHAN

List of diagnostic List of diagnostic imaging studiesimaging studies

Plain x-raysPlain x-rays CT scanCT scan MRIMRI Nuclear imagingNuclear imaging UltrasoundUltrasound MammographyMammography AngiographyAngiography FluoroscopyFluoroscopy

X-Ray Imaging

X-ray imaging is still one of the most important diagnostic methods used in medicine. It provides mainly morphological (anatomical) information - but may also provide some physiological (functional) information.

What are x-rays? No mass No mass No charge No charge Energy Energy

Basic x-ray physicsBasic x-ray physics X-rays: a form of electromagnetic X-rays: a form of electromagnetic

energyenergy Travel at the speed of lightTravel at the speed of light Electromagnetic spectrumElectromagnetic spectrum

Gamma RaysGamma Rays X-raysX-rays Visible lightVisible light Infrared lightInfrared light MicrowavesMicrowaves RadarRadar Radio wavesRadio waves

An X-ray machine is basically like a camera. It uses X-rays to expose the film, instead of visible light.

X-rays are similar to light in that they are electromagnetic waves, but they are more energetic so they can penetrate many materials to varying degrees. When the X-rays hit the film, they expose it just as light would. Various structures such as bone, fat, muscle, tumors and all other masses absorb X-rays at different levels

That X-ray light is very strong and is not visible to human eyes

X-rays can penetrate objects opaque. X-rays are commonly used to look at something we cannot see directly.

X-rays or Roentgen rays are a form of electromagnetic radiation

X-rays are commonly used in the diagnosis of medical images

X-rays are a form of ionizing radiation and can be dangerous.

Three things can happenThree things can happen X-rays can:X-rays can:

PassPass all the way all the way throughthrough the body the body Be deflected or Be deflected or scatteredscattered Be Be absorbedabsorbed

X-rays were discovered in 1895 when Wilhelm Conrad Roentgen observed that a screen coated with a barium salt fluoresced when placed near a cathode ray tube. Roentgen concluded that a form of penetrating radiation was being emitted by the cathode ray tube and called the unknown rays, X-rays.

First ever X ray in historyFirst ever X ray in history

X-rays Passing Through X-rays Passing Through TissueTissue

Depends on the energy of the x-ray Depends on the energy of the x-ray and the atomic number of the tissueand the atomic number of the tissue

Higher energy x-ray - more likely to Higher energy x-ray - more likely to pass throughpass through

Higher atomic number - more likely Higher atomic number - more likely to absorb the x-rayto absorb the x-ray

How do x-rays passing How do x-rays passing through the body create an through the body create an

image?image? X-rays that pass through the body to X-rays that pass through the body to

the film render the film dark (black)the film render the film dark (black) X-rays that are totally blocked do not X-rays that are totally blocked do not

reach the film and render the film light reach the film and render the film light (white)(white)

Air = low atomic # = x-rays get Air = low atomic # = x-rays get through = image is darkthrough = image is dark

Metal = high atomic # = x-rays Metal = high atomic # = x-rays blocked = image is light (white)blocked = image is light (white)

5 Basic Radiographic 5 Basic Radiographic DensitiesDensities

AirAir FatFat Soft tissue/fluidSoft tissue/fluid MineralMineral MetalMetal

Different tissues in body absorb Different tissues in body absorb X-rays at different extents:X-rays at different extents:

• Bone-Bone- high absorption (white)high absorption (white)

• Tissue-Tissue- somewhere in the middle absorption somewhere in the middle absorption (grey) (grey)

• Air- Air- low absorption (black)low absorption (black)

Main Parts of the X-ray Main Parts of the X-ray DeviceDevice

X-ray tubeX-ray tube

Voltage-Current GeneratorVoltage-Current Generator::- High Voltage TransformerHigh Voltage Transformer – supplies – supplies

high voltage (up to 150kV)high voltage (up to 150kV)- RectifierRectifier - - produces produces unidirectionalunidirectional tube tube

electron current electron current

Control panelControl panel – today most – today most parameters of the device (including parameters of the device (including voltage and current) are controlled voltage and current) are controlled by means of a computer. It is located by means of a computer. It is located outside the examination room or outside the examination room or behind a shield made of glass behind a shield made of glass containing lead (to protect the containing lead (to protect the radiological assistantradiological assistant

MainMain mechanical partsmechanical parts: tube stand, : tube stand, examination table, grid for removing examination table, grid for removing scattered photons (‘Bucky’), scattered photons (‘Bucky’),

X-ray detectorX-ray detector: cassette with : cassette with radiographic film and adjacent radiographic film and adjacent fluorescent screens (fluorescent screens (in radiographyin radiography) )

Passage of X-rays Passage of X-rays through Patientthrough Patient's Body's Body

X-rays emitted from a smallX-rays emitted from a small focal areafocal area of of the anode propagate in all directions. In the anode propagate in all directions. In the tube envelope, some low energy the tube envelope, some low energy photons are absorbed. Further photons are absorbed. Further absorption of absorption of thesethese photons occurs in the photons occurs in the primary filterprimary filter, made of aluminium sheet. , made of aluminium sheet. It absorbsIt absorbs low energy photons which low energy photons which would be absorbed by surface tissues would be absorbed by surface tissues and do not contribute to the image and do not contribute to the image formation (unnecessary patient dose). X-formation (unnecessary patient dose). X-ray beam is delimited byray beam is delimited by rectangular rectangular collimator platescollimator plates made of lead. made of lead.

The rays then pass through the body The rays then pass through the body where transmission or absorption orwhere transmission or absorption or scattering may occur. After that they scattering may occur. After that they pass through thepass through the gridgrid, which is in , which is in front of the detector to remove front of the detector to remove scattered photons as these would scattered photons as these would degrade the image. degrade the image.

WavelengthWavelength The wavelength The wavelength ( ( ) ) of x-ray range of x-ray range

10 nanometers to 100 picometers 10 nanometers to 100 picometers (with frequency (with frequency 10101616 Hz until 10 Hz until 102020 Hz Hz).).

These X-rays have a shape similar to These X-rays have a shape similar to that of ordinary light rays, infrared that of ordinary light rays, infrared and radio waves; differing only in and radio waves; differing only in terms of wavelength other features.terms of wavelength other features.

Electromagnetic Electromagnetic Spectrum Spectrum

Use of the Contrast Use of the Contrast AgentsAgents

The soft tissueThe soft tissuess only slightly only slightly differ in their attenuation. differ in their attenuation. Therefore they cannot be Therefore they cannot be distinguished in a common distinguished in a common radiograph. That is the reason radiograph. That is the reason for the use of pharmaceuticals for the use of pharmaceuticals calledcalled contrast agentscontrast agents. .

The attenuation of certain tissues can The attenuation of certain tissues can be increased or lowered.be increased or lowered. Positive Positive contrastcontrast is achieved by substances is achieved by substances having a high proton number as the having a high proton number as the probability of the photoelectric effect probability of the photoelectric effect is increased. A suspension of barium is increased. A suspension of barium sulphate, “barium meal”, is used for sulphate, “barium meal”, is used for imaging and functional examination of imaging and functional examination of GIT. In examinations of blood, biliary GIT. In examinations of blood, biliary and urinary vessels etc. compounds and urinary vessels etc. compounds with high content of iodine are used.with high content of iodine are used.

Hollow inner body organs can be Hollow inner body organs can be visualised byvisualised by negative contrastnegative contrast. . Air or better COAir or better CO22 can be used. can be used. The cavities are filled by gas, The cavities are filled by gas, inflated, so that they can be inflated, so that they can be visualised as structures of very visualised as structures of very low attenuation (pleural space, low attenuation (pleural space, peritoneum, brain chambers).peritoneum, brain chambers).

Positive and Negative Positive and Negative ContrastContrast

Contrast image of the appendix – diverticulosis – combination with negative contrast

Horseshoe kidney – positive contrast

Why is a lead shield/apron Why is a lead shield/apron placed on you when you get an placed on you when you get an

x ray?x ray? X-rays emit radiation which cause X-rays emit radiation which cause

mutations to healthy cells. X-rays are mutations to healthy cells. X-rays are only harmful if you are exposed to only harmful if you are exposed to them for a really LONG time. X-rays them for a really LONG time. X-rays you get at the doctors are okay you get at the doctors are okay because you don’t get them everyday. because you don’t get them everyday. X rays are more beneficial than they X rays are more beneficial than they are harmful because they can detect are harmful because they can detect problems that can be detrimental to problems that can be detrimental to your health.your health.

Different views Different views AP view AP view PA viewPA view Lateral Lateral

Can be obtained by changing the Can be obtained by changing the relative orientation of the body and relative orientation of the body and the direction of the X-ray beam the direction of the X-ray beam

The PA (postero-The PA (postero-anterior) viewanterior) view

It is the most It is the most frequently required frequently required radiological examination. radiological examination. Comparison of current film with old Comparison of current film with old films is valuablefilms is valuable

Position:Position: Patient facing the Patient facing the film, chin up with the shouldersfilm, chin up with the shoulders rotated forwards to displacedrotated forwards to displaced the scapulae from the lungs.the scapulae from the lungs. Exposure is made on fullExposure is made on full inspirationinspiration

AP view AP view The X ray beam enters through The X ray beam enters through

anterior aspect and exits through anterior aspect and exits through the posterior aspectthe posterior aspect

Lateral view:Lateral view:

The pt stands with both The pt stands with both arms raised and the left sidearms raised and the left sideof the chest pressed against of the chest pressed against a flat surface a flat surface

Lateral decubitus Lateral decubitus positionposition

It is helpful to assess the volume of It is helpful to assess the volume of pleural effusion and demonstrate pleural effusion and demonstrate whether a pleural effusion is mobile whether a pleural effusion is mobile or notor not

Lateral decubitus position film showing mobile pleural effusion (arrows

CT CT ScannerScanner Computed tomography or CT scan

works on the same principles as fixed

plate x rays, only with a CT scan, an x ray

tube rotates around the individual, taking

hundreds of images that are then compiled

by a computer to produce a two-

dimensional cross section of the body.

Although many images are taken to

produce a CT scan, the total dose of

radiation the individual is exposed to is

low.

Optimal Viewing Optimal Viewing Dedicated light sourceDedicated light source Darkened environment (like a movie Darkened environment (like a movie

theater)theater) Limit distractionLimit distraction

X-ray viewing station

Medical ImagingMedical Imaging Primary purpose is to identify pathologic Primary purpose is to identify pathologic

conditions.conditions. Requires recognition of normal anatomy.Requires recognition of normal anatomy.

Summary: Summary: How do x-rays create an How do x-rays create an image of internal body structures?image of internal body structures?

X-rays pass through the body to X-rays pass through the body to varying degreesvarying degrees

Higher atomic number structures Higher atomic number structures block x-rays better, example bone.block x-rays better, example bone.

Lower atomic number structures Lower atomic number structures allow x-rays to pass through, allow x-rays to pass through, example: air in the lungs.example: air in the lungs.