Medical Physics (Option 2)

Question 1

A-Scan

Answer 1

A method of scanning tissue that involves placing an ultrasound emitting transducer on the surface of the body, and then measuring reflections of emitted pulses. A-Scans are used to measure the foetal head size during pregnancy.

Question 2

Accommodation

Answer 2

The name given to the eye’s focusing process.

Question 3

Acoustic Impedance

Answer 3

The product of the speed of sound through a given medium, and the density of the medium.

Question 4

Air-Soft Tissue Boundary

Answer 4

A boundary at which nearly all incident ultrasound pulses are reflected, due to there being a very large acoustic impedance difference.

Question 5

Astigmatism

Answer 5

A sight defect caused by a misshapen cornea.

Question 6

B-Scan

Answer 6

A method of scanning tissue, used form more complex structures than A-Scans. Instead of the echo signals controlling the y-gain (as in A-Scans), they control the brightness of the oscilloscope spot. B-Scans are used to determine the placenta’s position during pregnancy.

Question 7

Barium Meal

Answer 7

A contrast medium that ensures that there is a significant difference between the density of the area being scanned and the rest of the body. Barium is chosen due to its high proton number. It is consumed by the patient.

Question 8

Bone-Soft Tissue Boundary

Answer 8

A boundary at which the acoustic impedance is very large. This means that ultrasound is more intensely reflected.

Question 9

Ceruminous

Answer 9

The wax glands that line the ear canal and protect the eardrum.

Question 10

Choroid

Answer 10

A layer of tissue containing blood vessels that carry oxygen and food to the eye. It lines the sclera.

Question 11

Ciliary Muscles

Answer 11

Circular muscle fibres responsible for making changes to the lens’ shape.

Question 12

Coherent Fibre Bundle

Answer 12

A bundle of fibres in which each fibre is positioned in an orderly fashion.

Question 13

Cones

Answer 13

A light sensitive cell that is used to detect light intensities. Each cone is connected to a nerve fibre that joins it to the brain and so results in detailed, colour images.

Question 14

CT Scans

Answer 14

A scanning method that produces a cross section of the body by rotating a monochromatic x-ray beam around it, in combination with a series of detectors. Whilst it produces higher resolution images than ultrasound and is non-invasive, it is highly ionising and costly.

Question 15

Decibel

Answer 15

The unit used for sound intensity.

Question 16

Flat Panel Detectors

Answer 16

A light detecting panel that is used in medical imaging. They are faster and more sensitive to light differences than traditional film.

Question 17

Gamma Camera

Answer 17

A type of detector used in PET scanners, consisting of a photomultiplier tube that converts gamma photons into electrical pulses.

Question 18

Gelatinous Vitreous Humour

Answer 18

The fluid found between the lens and the retina in the human eye.

Question 19

Hypermetropia

Answer 19

The name given to long-sightedness.

Question 20

Incoherent Fibre Bundle

Answer 20

A bundle of fibres in which the fibres have not been orderly arranged. They are only suitable for the transportation of light.

Question 21

Iris

Answer 21

A coloured region of the eye that is partially responsible for controlling the amount of light that enters.

Question 22

Linear Attenuation Coefficient

Answer 22

X-rays attenuate when they pass through matter. The linear attenuation coefficient is the ratio of the fractional reduction of intensity over the thickness of the layer.

Question 23

Magnetic Resonance Imaging

Answer 23

A scanning method that involves the patient lying in a very strong cylindrical magnet. Electromagnetic radiation is emitted that causes a reorientation of hydrogen nuclei. When they return to their original positions radiofrequency radiation is emitted and detected.

Question 24

Mass Attenuation Coefficient

Answer 24

The linear attenuation coefficient divided by the density of the material being passed through.

Question 25

Myopia

Answer 25

The name given to short-sightedness.

Question 26

Optic Papilla

Answer 26

A region of the retina that contains no rods or cones and so isn't sensitive to light. It is also known as the eye's blind spot.

Question 27

Piezoelectric Effect

Answer 27

An effect shown by crystals like quartz. When a potential difference is applied, the crystal will deform. Likewise, when the crystal is deformed, a potential difference is produced.

Question 28

Positron Emission Tomography Scans

Answer 28

A scanning technique that produces cross-sectional and 3D images. It involves a radionuclide being injected into the body, which then releases gamma photons that are detected by the scanning machine.

Question 29

Retina

Answer 29

The light-sensitive region, found at the back of the eye.

Question 30

Rods

Answer 30

A light-sensitive cell that is used to detect low light intensities. they produce grayscale images with limited detail.

Question 31

Scintillator

Answer 31

A device that converts x-ray photons into light photons.

Question 32

Sclera

Answer 32

A coating that covers the entire eye. It is clear in front of the cornea but is opaque around the remainder of the eye.

Question 33

Suspensory Ligament

Answer 33

Responsible for holding the lens of the eye in place.

Question 34

Transducer

Answer 34

A device that contains a piezoelectric crustal. In medical contexts, they are responsible for producing pulses of ultrasound, as well as acting as a detector for ultrasound echos.

Question 35

Ultrasound

Answer 35

Sound waves with a frequency higher than the upper frequency audible to the human ear (20kHz)/

Question 36

Visual Purple

Answer 36

A compound found in rods, that is bleached by light. The bleaching is reversed by enzymes. The reversal process is fastest under low light intensities and so the rods are more sensitive in low-light environments.

Question 37

Watery Aqueous Humour

Answer 37

The fluid found between the lens and the cornea in the human eye.