Medical Imaging

bone

X-rays mostly pass through skin and soft tissue, but they can't easily pass through ___ so can be used in diagnostic imaging

X-rays

___ can also be used to examine organs and identify problems such as pneumonia.

Transparent

Air is ___ to x-rays, where x-rays get through you get a dark image

opaque

bones are quite ___ to x-rays and soft tissue is slightly ____.

fluoroscopy

shows organs functioning in real time with x-rays

contrast

the ___ of x-rays can be increased by using material/dye that is opaque to x-rays.

tungsten target

electrons are emitted from the heated filament towards the ___ ___ due to the very potential difference between them.

wasted as heat, undergo transitions, deflected and slowed down

when electrons jump across they do 1 of 3 things:

most of them get ___ ___ ___

some ___ ____

some are ___ ___ ___ ___

copper mounting

the tungsten target has a ____ ____ because it conducts heat and is cooled by circulating oil through the mount. Spinning the tungsten target at high speed also helps to stop it overheating.

characteristic x-rays

When electrons jump across to the tungsten target some undergo transitions and release energy in the form of ___ ___.

continuous x-rays

produced when electrons are deflected and slowed down, shown as the continuous line on the graph.

intensity

___ = number of x-rays

Current

___ = carrier

voltage

the higher the tube ___, the higher the maximum frequency so the higher the maximum x-ray energy.

metal filter

when an x-ray is taken a ___ ___ is placed between the X-ray tube and the patient. This filters out low energy x-rays (soft) which would be absorbed by the skin and other soft tissues which could become damaged. This results in a 'hard' x-ray.

High voltage

better contrast because the highest energy has increased. But if it gets too high a lot of high energy x-rays would go straight through and so there would be no contrast left - a blank dark image.

high current

more intensity, but if it gets too high there will be too many high energy x-rays so the image would end up too dark because too many x-rays went through.

with filters

reduces the intensity and blocks out the weak energy x-rays which would be absorbed too quickly by the patient. Better quality x-rays means a better quality image.

CT scan

uses specialised x-ray equipment to produce cross-sectional images of the body. Contrast dye is often used to make structures more visible. 3D images can also be made.

CT scan uses

often the best method for detecting cancers such as lymphoma, cancers of the lung, liver, kidney ovary and pancreas. Also used to detect pulmonary embolisms.

Attenuation

is the reduction in strength of the x-ray as it passes through a material. The higher the number the more has been absorbed (lost).

Filtered back projection

the algorithm used to create a CT image from attenuations.

advantages of x-rays

- can easily spot bone or contrast mediums in tissues.

- can treat some cancers

- non-invasive

-no discomfort whilst procedure is taking place

- good resolution

disadvantages of x-rays

- ionising radiation so can damage healthy cells

- if a contrast medium is used there is a risk of an allergic reaction

- must have a trained operator to be effective

- equipment is expensive

- needs constant cooling

- can be hazardous to the operator

sound waves

___ ___ are formed when something vibrates, the vibrations pass through air by making air molecules vibrate. These vibrations are picked up by the ear.

piezoelectric crystal

a ____ ____ has an alternating current applied across it - this causes it to vibrate producing the ultrasound. The ultrasound then bounces back off an organ and hits the ____ ____ again, this causes it to vibrate which then produces an alternating current again.

frequency, time between signals

in ultrasound scans by measuring things like the ___ and ___ ___ ___, a computer can produce images, calculate depths and speeds.

density, elasticity, texture

ultrasounds will bounce back when there is a difference in ___, ___, and/or ___ - this is a boundary.

boundaries, acoustic impedance

the reflected signals of ultrasounds are less intense than the generated signals because some of the signal will be lost at the ___ and some lost in ___ ___.

ultrasound uses

- imaging soft tissue and soft structures in real time

- measuring flow speeds

- is non invasive and non ionising

acoustic impedance

is a materials property that resists the passage of ultrasound

density, normal speed

a materials impedance will depend on its ___ and the ___ ___ of sound in the material.

boundaries, acoustic impedance

ultrasound loses intensity at ___ and because of ___ ___.

weaker

ultrasound gets ___ as it passes through a material - this is acoustic impedance.

doppler shift

is the difference between the transmitted and received frequencies - often in the audible range..

frequency

there is a change in ___ if there is a change in distance between the source and the sensor.

transmitted, received

____ and ____ frequencies are usually in the MHz range.

reflected frequency towards

___ ___ ___ = transmitted frequency + doppler shift

reflected frequency away

___ ___ ___ = transmitted frequency - doppler shift

blood flow

a doppler flow meter is used to measure the speed of ___ ___.

colour doppler

___ ___ is a type of ultrasound based diagnostic imaging technique. A computer converts doppler sounds into colours that are overlaid onto the image of blood vessels. The colours represent the speed and direction of blood flow through a vessel.

speed, direction

colour doppler is a type of ultrasound based diagnostic imaging technique. A computer converts doppler sounds into colours that are overlaid onto the image of blood vessels. The colours represent the ___ and ___ of blood flow through a vessel.

Advantages of ultrasound

- can see tissues without a contrast medium

- can break kidney stones

- non ionising

- non invasive

- no/or little discomfort whilst procedure is taking place

- more effective than x-rays at looking at soft tissues

- equipment is relatively cheap

- not hazardous to the operator

disadvantages of ultrasound

- must have a trained operator to be effective

- less effective than x-rays at looking at hard tissue

- poor resolution

- not good for full body imaging

- not good for imaging the lungs due to air

Nuclear medicine

In ___ ___, radioactive tracers can be used to see how well organs in your body are working or to find areas of disease. These are attached to a specific compound that will collect in the organ of interest. By detecting the radiation to see for abnormal absorption we can examine that organ.

tracers

In nuclear medicine radioactive ___ can be used to see how well organs in your body are working or to find areas of disease. These are attached to a specific compound that will collect in the organ of interest. By detecting the radiation to see for abnormal absorption we can examine that organ.

Disadvantages of nuclear medicine

- generally poor resolution

- radiation risk

- invasive

- radioactive waste

- relatively high cost

Iodine-131

used to treat patients with an overactive thyroid or thyroid cancer as the Beta can destroy part of the thyroid.

Iodine-123

used to detect the functioning of the thyroid gland during medical imaging. The thyroid gland naturally takes up iodine from the diet to make hormones to regulate metabolism. So will naturally absorb the _____.

Technetium-99m

the most commonly used isotope in diagnositic nuclear medicine. Can be attached to a specific compound which will collect in the organ of interest to allow you to assess functioning by seeing whether it has been abnormally absorbed. E.g. Can be attached to calcium which will be absorbed by bone, abnormal absorption would indicate a problem such as cancer.

Half life of the tracer

long enough to examine metabolic processes but short enough to minimise exposure to the patient.

Range of the tracer

Needs to be gamma in order to penetrate out of the body but not too high energy as would be so strong it would not be possible to produce an image.

Activity of the tracer

Not too big to cause the patient damage but not too small otherwise will not give off enough gamma in order to produce an image.

Collimater

The ____ only allows gamma rays through that are coming close to head on, so that a sharper image can be formed due to knowing where the ray has come from.

scintilate

When gamma rays hit the crystals the crystals ___ producing flashes of light.

photomultiplier tubes

___ ___ electronically multiply the flashes of light which are then picked up by light sensors passed onto electronics and computers for processing an image.

Gamma camera

the patient is injected with a specific nuclear tracer which will collect in the organ of interest. After some time the patient is placed in front of a ___ ___..

nuclear medicine uses

- structural and functional images of organs

- whole body scanning

- analyse kidney and spleen function

- image blood flow and function of the heart

- determine the presence and spread of cancer

- measure thyroid function, detection of an over active or under active thyroid and cancer

- identify bleeding in the bowel

- locate the presence of infection

MRI

___ is an imaging technique that uses strong magnets together with sophisticated computers to build up images of the body.

Advantages of MRI

- safe: no use of ionising radiation

- images can be obtained in any body plane

- good for viewing soft tissue, fat, and water

- image can be varied to show different tissues more clearly

- body function and chemistry can be investigated as well as structure

Disadvantages of MRI

- expensive

- can require a high level of expertise to interpret images

- process can be difficult as is claustrophobic, can take a long time, must keep still and is noisy

- practical problems associated with magnets: patients must take off all metal, and patients with metal implants that contain iron, nickel or cobalt cannot be scanned.

Precession

The change in orientation of the rotational axis - everything that spins wobbles, this is known as ___.

spin

All particles have a quantum property called ___.

electromagnetic field

Each spinning hydrogen proton acts like a tiny bar magnet, when the patient is placed inside the MRI scanner the proton spin axis lines up with the ___ ___ inside the scanner.

radio frequency

the ___ ___ is then switched on to make the protons resonate. This is a specific ___ ___ so that it only interacts with the hydrogen protons.

resonate

the radio frequency is then switched on to make the protons ___. This is a specific radio frequency so that it only interacts with the hydrogen protons.

precess at 90 degree's

The protons resonate (excite) and their energy level begins to increase causing them to ___ ___ ___ ___ to the magnetic field.

radio frequency

the ___ ___ is then switched off. The hydrogen protons begin to relax and move back to being aligned with the magnetic field. During this relaxation time they transmit a ___ ___ signal.

receiver coils

The ___ ___ detect the radio frequency signal given off by the protons and use the signal as well as the relaxation time to process an image.