2. The physical properties of electromagnetic radiation can

be used as diagnostic tools

In 1895 Wilhelm Roentgen discovered X-rays.

Above is an x-ray of his own hand.

describe how X-rays are currently produced

Copper Anode with Tungsten face.

Cathode (Heated Filament)

describe how X-rays are currently produced

An x-ray tube is just a modified cathode ray tube.

Electrons are emitted by thermionic emission at the cathode and are accelerated by a large potential difference towards the anode.

X-rays are produced in two ways when the electrons strike the anode.

describe how X-rays are currently produced

1. As the electrons decelerate at the anode their kinetic energy is transformed into x rays (general x-ray spectrum)

Energy conversion

Kinetic x-rays

x-rayx-rayphotonphoton

ttrraannssii ttii oonn

K L M N

Electron

Ejected electron

describe how X-rays are currently produced

2. High energy electrons collide with inner shell electrons in the Tungsten target ejecting them from their shell.

As an outer shell electron falls in to a lower energy level it releases an x-ray photon. (Characteristic radiation)

compare the differences between ‘soft’ and ‘hard’ X-rays  

Hard X-Rays Soft X-Rays

- Higher Frequency, Smaller Wavelength λ ~0.01nm

- Lower Frequency, Larger Wavelength λ ~1nm

- Closer to the gamma ray spectrum

- Closer to the UV ray spectrum

- Higher penetration (photons have more energy)

- Lower penetration (photons have less energy)

- Produces higher “quality” x-rays

- Produces lower “quality” x-ray

- Higher voltages are required to produce

- Lower Voltages are required to produce

Explain how a computed axial tomography (CAT) scan is produced A CT or CAT scan is a

tomographic image(slice) of the body.

A narrow sector-shaped x-ray beam is passed through the body falling on a linear array of detectors on the opposite side of the body

The x-ray source and detectors are rotated around the body, passing the x-rays through the body at different angles

explain how a computed axial tomography (CAT) scan is produced

The detectors measure the varying transmission intensity of the x-rays at different angles, sending the data to a computer.

The computer uses the data to construct a tomographic image showing a sectional view through the body in the plane of the original rotating sector beam.

gather information to observe at least one image of a fracture on an X-ray film and X-ray images of other body parts

Oops ! A broken wrist

describe circumstances where a CAT scan would be a superior diagnostic tool compared to either X-rays or ultrasound

Normal x-rays(right top) produce an image of the entire thickness of the body.

Structures therefore overlap and and can be difficult to identify.

A tumor in the lungs would be difficult to identify with x-rays but with a CT scan (right) you could view detailed images of inside the lungs.

describe circumstances where a CAT scan would be a superior diagnostic tool compared to either X-rays or

ultrasound Ultrasound can obtain an image of soft tissue but only when the tissue is not obscured by bone.

Ultrasound cannot be used to image the brain because of the large reflections from the scull.

Thus CT scans are better for examining brain tumors.

CT scans also have the advantage of higher resolution and thus can diagnose much smaller structures such as early tumors.

Question Set 11. Identify the term for producing a

cross-sectional slice image of the body.

2. Explain why a high voltage is needed to produce x-rays in a CRT.

3. Discuss the use of ultrasound instead of CAT scans to diagnose problems in unborn children.

Question Set 21. Frank is rushed to the hospital after a

physical game of football and has a suspected hairline fracture of a rib. The doctor orders an x-ray even though it may not show the tiny fracture. Account for the doctors decision.

2. Joey the legend league player gets yet another knee injury. The doctor opts for a CAT scan instead of either an x-ray or ultrasound scan. Account for the doctors decision.

explain how an endoscope works in relation to total internal

reflection Endoscopy is the medical examination of the interior of the body by inserting an optical tube (an endoscope) through an opening in the body.

explain how an endoscope works in relation to total internal reflection

Endoscopes use the process of total internal reflection to transfer light along the individual fibers which make up the endoscope.

As light passes from a more optically dense medium(glass) into a less optically dense medium it refracts. (figure A)

If the angle of incidence (i) exceeds the critical angle then the light will reflect inside the material instead of refracting outside it(total internal reflection).

A

B

explain how an endoscope works in relation to total internal reflection

A typical optical fiber is shown on the right. The parts are :

Core the inner light-carrying member.

Cladding the middle layer, which serves to confine the light to the core. It must have a lower refractive index than the core.

Buffer the outer layer serving to protect the core and cladding from damage.

discuss differences between the role of coherent and incoherent bundles of fibers in an endoscope

The arrangement of fibres in a coherent bundle is represented schematically in the diagram (left). Coherent fibres are used to transport images from inside the body.The individual fibres in the pipe must be in the same position relative to each other at the start and the finish.

discuss differences between the role of coherent and incoherent bundles of fibers in an endoscope

In a non-coherent fibre bundle, one or more of the fibres swap positions relative to each other at opposite ends of the fibre.

Incoherent fibres are used to transport light along the endoscope but cannot be used to transport an image.

    explain how an endoscope is used in:– observing internal organs– obtaining tissue samples of

internal organs for further testing Incoherent fibres to transmit light to the point of observation.

 Coherent fibres to carry the image back to the observer from the tissue being observed

 A system of lenses to focus an image of the tissues under examination onto the optical fibre bundle.

Suction tube to remove blood and other loose tissue material

Miniature remote controlled surgical instruments

gather information to observe at least one image of a fracture on an X-ray film and X-ray images of other body parts

X-rays of internal organs can be obtained by having patients ingest barium sulfate which is opaque to x-rays.

gather secondary information to observe a CAT scan image and compare the information provided by CAT scans to that provided by an X-ray image for the same body part (chest)

CAT Scan X-ray2 dimensional slice Entire thickness

converted into a 2D image

No overlap of body parts

Overlap makes it difficult to see internal structures

Very high resolution Reasonable resolution (sometimes blurry)

Can image soft tissue Can only image hard tissue

gather secondary information to observe internal organs from images produced by an endoscope

Stomach ulcer Anterior Cruciate ligament

gather secondary information to observe internal organs from images produced by an endoscope

Tools can be inserted with the fibre optic cable so a doctor can manipulate the tools while watching a television screen.

Question Set 31. Define the term critical angle.2. Contrast coherent and incoherent

bundles of fibres.3. Explain why optical fibres have a coating

of lower refractive index material.4. Discuss the use of endoscopes in

internal surgery.5. Outline how it would be possible to

increase the resolution of the image transported by a bundle of coherent optical fibres