Medical Physics for 2022 AQA A levels

accomodation

the process by which the eye's lens changes shape to focus near or far objects on the retina

astigmatism

a condition in which the eye does not focus properly because of uneven curvatures of the cornea

Symptoms of Astigmatism

focussed on one plane, unfocussed on the perpendicular plane

barium meal

a contrast medium consumed by patients, chosen due to high density

ceruminous

wax glands that line the ear canal and protect the eardrum

ciliary muscles

Circular muscles that relax or contract to enable the lens to change shape for focussing

cones

retinal receptor cells that are concentrated near the center of the retina and that function in daylight or in well-lit conditions. They detect fine detail and give rise to color sensations.

CT scan (computed tomography)

a series of x-ray photographs taken from different angles and combined by computer into a composite representation of a slice through the body

Benefits of CT

-Non-invasive

-Good detail of solid organ and bone

-Relatively fast, limited motion artefact

-Readily available

Disadvantages of CT

-Radiation exposure

-Weight limit of patient (~350 lbs)

-Metal will obscure imaging

-Relatively expensive

Decibel

Unit of sound intensity

Hypermetropia

long-sightedness

iris

a ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening

linear attenuation coefficient

the amount of x-ray beam that is scattered or absorbed per unit thickness of the absorber

Mass attenuation coefficient

Linear attenuation coefficient / density

magnetic resonance imaging (MRI)

a technique that uses magnetic fields and radio waves to produce computer-generated images that distinguish among different types of soft tissue; allows us to see structures within the brain. SPIN

myopia

shortsightedness

rods

retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision, when cones don't respond

suspensory ligaments

A series of fibres that hold the lens of the eye in place

power of a lens

1/focal length

m

v/u

1/f

1/u + 1/v

I0

10^-12 W/m^2

intensity level

10 log 𝐼/𝐼0

I

𝐼0𝑒-𝜇x

𝜇m

𝜇 / p

intensity

ln2 / 𝜇