Aspects of Medical Imaging and Technology

What does traditional MRI image?

proton content

What are specialised, newer MRI machines image?

noble gases

What is an analogue measurement?

When a quantity is continuous

What is a digital measurement?

When a quantity is discrete

What does ADC stand for?

Analogue-Digital Converter

What is the role of the transducer?

To convert the physical interaction into an analogue mA or mV signal that can be passed to the ADC

What is the shape of pretty much every transducer response curve?

What is noise?

about randomness - for the same input do you get the same output, how reproducible is it?

What is saturation?

The point at which a change in input solicits no change in output, often associated with overdriving the input

What is linearity?

The extent to which a doubling of the input provides a doubling of the output

What is the best place of the transducer response curve to operate the transducer?

The central, most linear part

What is dynamic range?

The range over which the response of the transducer is dynamic

What is dynamic range limited by?

Limited by ADC min/max input

What is clipping?

When the signal exceeds the min/max limit of the ADC

What is resolution?

how fine-grained the response is

What is the resolution of an analogue system limited by?

Noise

How do you maximise resolution (bit depth)?

Having a large number of samples, and for the steps to be as small as possible

What is the risk for medical imaging if the bit depth is too small?

Doctors cannot distinguish differences in image (e.g. differences in tissue density) for diagnosis

What is the digital acquisition chain?

Analogue physical interaction

Transducer monitors magnitude of the interaction and converts it to a representative mA/mV

The mA/mV signal is passed to the ADC which generates a binary representation of the transducer signal

The binary value is passed to the computer for manipulation and processing

What is the purpose of the latch?

The latch sits between the ADC and the computer and holds the most recent digital value

It helps to control the rate at which data is fed to the computer so it has adequate time to process it

What is the Nyquist sampling limit?

Nyquist sampling limit says that you must sample at twice the frequency of interest

What is the full flow chart of imaging from acquisition to image?