Image perception:

Visual system:

Occurs when eye focuses light on retina

Retina

Has layer of photoreceptors which detect light photons and respond by producing natural impulses

Perception process

Stimulus energy - reception - transduction - transmission - brain receiving

Stimulus energy

Electromagnetic energy

Reception

Receptors in eye detect and respond to light

Transduction

Light converted from electromagnetic energy to energy in form of neural impulses

Transmission

Sent to Brian via optic nerve

Receiving last step of perception process

Received in primary visual cortex and imperfection occurs in that area

Perception grouped into 5 categories

Stimulation

Organization

Interpretation and evaluation

Memory

Recollection

Types of optical illusion

Physical

Physiological

Cognitive

Physical optical illusion

Create images that are different from object

Physiological

Effect as a result of excessive stimulation

Cognitive

Result of unconscious interference

saccade

Rapid eye movement involved in visual scanning. Bring the stimuli on to the fovea

Fixation time

Time that person gaze remained fixated on stimulus. This time is the criterion.

Visual search

Radiographer searching image for target and useful visual field. Target: visual stimulus being searched for.

Search error -

observer fails to fixate the target or fixation is not within the useful visual field.

Detection error

observer has adequately fixated on or close enough to the target for a short period of time but fails to detect. Fixation is below the criterion time for detection.

Interpretation error

observer has fixated closer time more than criterion time but fails to detect it as a stimulus. Target observed but not identified.

Mach bands

Exaggeration of contrast between borders. Source of diagnostic area

Incidental findings

Findings of possible clinical significance that were not the main object of search. Diagnosed in asymptomatic / symptomatic patient undergoing.

Improving perception

• perception depends on attention

• Experience knowledge/ training

• Expectation quicken perception

Lateral inhibition:

Capacity of an excited neuron to reduce the activity of neighbors. It makes darker area seem darker than it is and lighter area seem lighter than it is

Reception

Receptors in eye detect and respond to light

Transduction

Perception cannot be reduced to its individual sensory components or the physical attributes. How we group objects visually

Visual system:

Occurs when eye focuses light on retina

Background illusions

How well an object is visualised depends on the background it is on. Grey cackle ackground can affect images.

Gestalt theory

Perception cannot be reduced to its idndividual sensory components or physical attributes.

Paredolias

When an object looks like something else.

Digital image precessing

Is a matrix of many small elects or pixels, each pixel represented by numerical value that computer uses

Pixel bit depth

Number of bit/ binary values means more variety of grey scale. Less bits is more range of colours.

Post processing examples

• grey scale processing

• Spatial filtering

• Dynamic control

LUT look up tables

Pre calculated data (Numberic information ) stored in the computer that is used to substitute new values for each pixel during processing

Dynamic range

Digital detectors have wide exposure latitude - range of receptor exposures over which an image and contrast will formed

Spatail request processing

• series of different algorithms used to post process the image.

• Edge enhancement/ sharpness to increase the detail by sharpening edges

PACs vs VNA

When image is stored in pacsa there tags added and this varies between vendors so the final medical image is not compatible.

VNS is capable of managing imaging data from different PACs repositories therefor increasing the health care provider control over medical data

VNA allows health acre providers to migrate from one vendor to another without worrying about imaging data loss

Interobability standard utilised in health care

DICOM - digital imaging communications in Medicine)

• Make medical imaging more interoperable.

• International standard to transmit store retrieve print process and display medical imaging information

Interoperability standard utilised in health care

Unique identifiers - guaranteed to be unique among all identifiers used for those objects in database

Can be allocated to every data item within a database and for a specific purpose