Lecture 16 + 17- Modelling

Question 1

What is the primary aim of a diagnostic model?

Answer 1

To quantify a characteristic of a system that determines the current health or disease.

Question 2

What is the primary aim of a prognostic model?

Answer 2

To predict how health or disease might evolve in the future.

Question 3

How should model complexity be determined?

Answer 3

The model should be no more complex than necessary otherwise waste resources, difficult to parameterise etc

BUT complex enough to capture key phenomena to answer specific questions

Question 4

Steps of patient specific modelling?

Answer 4

1. Acquisition of the geometry (scanning, segmentation etc)
2. Computation analysis
3. Data post processing

Question 5

What is an idealised model?

Answer 5

Simplified representation which capture key features

Question 6

What is image guided modelling?

Answer 6

Integration of imaging with computational modelling

Question 7

What are the 4 main reasons for the increase in patient specific modelling since 2000?

Answer 7

Improvements in computer power (Moore’s law)

Improvements in modelling software (ANSYS, Abaqus etc.)

Availability of high-resolution medical imaging (MRI etc.)

Potential of biomechanical measurements for clinical decision-making and surgical planning

Question 8

What features would the ideal imaging modality possess?

Answer 8

High resolution, low noise, artefact free, high contrast between tissues

Question 9

Which imaging modality comes closest to the ideal? Why?

Answer 9

CT (Computed Tomography) - It can distinguish the thrombus from the lumen in aneurysms.

Question 10

Main problems with CT for aneurysmal modelling?

Answer 10

It cannot measure wall thickness due to resolution limitations and insufficient contrast between tissues

In atherosclerosis, the resolution cannot show detailed structural differences in the plaque

Question 11

Main advantages of MRI?

Answer 11

Image contrast is higher to distinguish between tissues, and can enable some visualisation of aortic wall

It enables visualisation of atherosclerotic plaque components

Question 12

Main disadvantages of MRI?

Answer 12

Data acquisition times are long, patients must hold their breath to image, but this comes with significant noise

XY resolution is great, but slice thickness is much greater than CT and so Z resolution is poor. This makes it very difficult to measure WSS

Question 13

Main advantages of ultrasound?

Answer 13

Ultrasound data may be acquired using externally produced transducers

State of the art ultrasound gives excellent resolution for PSM

Question 14

Main disadvantages of ultrasound?

Answer 14

There are problems in practise with registration, low resolution, and loss of data due to to calcifications and bowel gas

Question 15

How can you mitigate the limitations of ultrasound?

Answer 15

By using intravascular ultrasound (higher frequency) where the transducer is placed inside the vessel

Question 16

What is optical coherence tomography (OCT)?

Answer 16

Use of coherent light to capture micro-resolution (it is effectively optic ultrasound)

Question 17

Main advantages and disadvantages of OCT?

Answer 17

Extremely high resolution (higher than any other modality), and instant imaging

But it is an invasive technique

Question 18

What is segmentation?

Answer 18

Identification of surfaces of interest in the organ

It can be manual, automated or semi-automated

Question 19

What must happen after segmentation of a surface and why?

Answer 19

Geometry must be further prepared to remove artefact and smooth the surface, so that it is reflective of reality

Question 20

What happens in modelling after the geometry is obtained?

Answer 20

Mesh generation, Computational modelling, and post processing.

Question 21

What are some problems associated with the increasing use of AI and machine learning in modelling?

Answer 21

AI/ML produces outcomes based on previous inputs from a data set. Therefore acts as a “black box” and does not have explanatory power based on physical understanding.

Question 22

What are the pros of a 0D model?

Answer 22

can be used to describe system-level response and interaction with different organs

directly comparable with clinical measurements

no need of expensive computing resources

Question 23

What are the cons of a 0D model?

Answer 23

frequency-domain representations neglects convective acceleration term

not capable of representing pulse wave propagation, WSS/pressure
distributions, etc.

some model parameters difficult to identify, easily affecting accuracy of results