Medical Imaging

Question 1

Name different examples of Imaging Systems.

Answer 1

MRI, Ultrasound, CT, X-rays, PET, SPECT and Endoscopy/ Laparoscopy.

Question 2

Explain the details of a MRI scan.

Answer 2

MRI - Magnetic Resonance ImagingMakes use of superconducting magnets (PM), which cause alignment of the hydrogen nuclei (contained in the water molecules of the body). Emits Radio Frequency from the RF coil which is absorbed by the protons (of the hydrogen nuclei), ‘causing a change in their direction’. The RF emission is then halted causing the protons to return to their original alignment - emitting their own radio signals in the process.These signals are detected and computationally constructed into a 3D image.

Question 3

Name the pros and cons of MRI.

Answer 3

PROS - MRI can target different regions of the body by focusing RF to different areas. Also no harmful radiation is used. CONS - Can result in Electromagnetic burning if not used properly, also creates a lot of ‘noise’.

Question 4

Explain the details of a Ultrasound scan.

Answer 4

Makes use of high frequency broadband (sound waves) that are reflected by tissue and received to create 3D images.

Question 5

Name the pros and cons of Ultrasound.

Answer 5

PROS - Produces real time images. No radiation is uses. CONS - Depending on the composition of the tissue signals may travel at different speeds, resulting in different intervals for being received. Therefore producing varying results.Tendency to thermal (depending on the apparatus)and speckle noise.

Question 6

Explain the details of a CT scan.

Answer 6

CT - Computed Tomography A X-Ray beam is rotated around the target area of the patient passing radiation through. The radiation is then picked up by sensors on the apposing side producing a thin 2D image. A computer then constructs a 3D image by combining all the 2D cross sections. (Makes use of the inverse of Radon transform).

Question 7

Name the pros and cons of CT scans.

Answer 7

PROS - Produces sharp and accurate images.CONS - Makes use of radiation so repeated scans must be limited.

Question 8

Explain the details of a X-Rays.

Answer 8

An electron beam (X-ray photons) passes through soft tissue producing a black image on back-projection ‘slide’.However the radiation is unable to pass through dense materials such as bone and instead is absorbed. Therefore a white image is then produced on the back-projection ‘slide’. Discovered by Wilhelm Röntgen.

Question 9

Name the pros and cons of X-Rays.

Answer 9

PROS - The best way to produces specific images of bones and other dense structures.CONS - Makes use of radiation so use must be restricted.

Question 10

Explain the details of a PET scan.

Answer 10

PET - Positron Emission TomographyRadioactively doped sugars (tracer fluids) are injected into the body. The sugars are then absorbed by tissues which have higher levels of activity.Gamma ray detectors arranged around the patient then pick up resulting collisions providing functional information about the area. This is done through the study of computer generated 3D images (using the same technology as CT scans).

Question 11

Name the pros and cons of PET scans.

Answer 11

PROS - Provides information about the functionality of the tissue (E.g. Heart irregularities) CONS - High doses of radioactive sugars injected is dangerous.

Question 12

Explain the details of a SPECT scan.

Answer 12

SPECT - Single Photon Emission Tomography Integrates CT and PET (radioactive sugar) technologies.Tracer is used to allow doctors to view blood flow in tissue and organs. A CT scan and PET scan are then computationally combined to produce a 3D image.

Question 13

Name the pros and cons of SPECT scans.

Answer 13

PROS - Provides detailed images of how the blood travels through the body and shows its paths (areas such as the brain).CONS - Makes use of radiation all be it less than CT and X-rays.

Question 14

Explain the details of processes such as Endoscopy and Laparoscopy.

Answer 14

Both make use of a robotic camera which is inserted into a specific orifice to give a detailed digital view of the inside of the body.

Question 15

Explain the pros and cons of processes such as Endoscopy and Laparoscopy.

Answer 15

PROS - Relatively easy procedure that prevents further surgery.Provides a real time view of inside the body. CONS - Equipment can be expensive and patient may be uncomfortable with the procedure.

Question 16

What is the definition of a digital image?

Answer 16

A numeric representation of spatial information with contrast based on physical properties.

Question 17

Name features of optical imaging.

Answer 17

Photoelectric effect, RGB and IGR.

Question 18

Describe the photoelectric effect.

Answer 18

The idea that electromagnetic radiation is made up from a series of particles known as photons.

Question 19

Describe how RBG is used when storing an image.

Answer 19

Each pixel holds a 3 digit value which represents the intensity of Red, Green and Blue (E.g. 5,0,3). The value is obtained through the use of a filter layer and a sensory array when the image is taken.

Question 20

Describe IGR.

Answer 20

IGR - Image Guided Radiotherapy Is a method of radiation therapy which incorporates imaging techniques during each treatment session. Uses high energy beams to control tumours, ensuring that radiation is only targeted toward treatment area. Use of high radiation always carries a risk.

Question 21

Name the common issues with Medical Imaging.

Answer 21

Image Reconstruction, Image Registration, Image Segmentation, Image processing, ‘Noise’, Network issues.

Question 22

Describe methods of Image Reconstruction.

Answer 22

Simple Back-Projection, Filtered Back-Projection, the use of a different image contrast medium.

Question 23

Describe Simple Back-Projection.

Answer 23

Simple Back-Projection - the projection of a image onto the back of a translucent screen. Start with a empty matrix, spread the intensity values across the matrix for each line of sight. Where the intensity is the highest that will be the focal point of the image. Produces a very blurry image however is very straight forward.

Question 24

Describe Filtered Back-Projection.

Answer 24

Filtered Back-Projection - Reduces the blurring of SBP by filtering each view before back-projection. The filtered images are then back-projected together to produce a near identical image.

Question 25

Describe the how image contrasts mediums differ.

Answer 25

Different mediums can be used to enhance the contrast of the structures of fluids within the body. (E.g. looking at blood vessels).Make use of the relationship between the hounsfield unit and greyscale.

Question 26

Describe issues and their solutions resulting from image registration.

Answer 26

Issues - Patient movement. Knowing the position and angle of acquisition. Scanning at different intervals results in internal and external change. Different length and thickness of slices depending on the angle. Solutions - Use markers to maintain positioning (internal or external).

Question 27

Describe network issues resulting from Medical Imaging.

Answer 27

Problems - ‘Big Data’ issuesFast processing machines are required as well as speedy networksGraphical displays are needed to kept up to date to view images. What format should the Data be stored? - DICOM (Digital Imaging and communications in medicine)

Question 28

Explain Image Segmentation and its methods.

Answer 28

Process of partitioning an image into different segments. (E.g. separating the organs and the tumour) A computer can segment an image into different groups of pixels (super pixels) depending on their factors (colour, intensity texture, etc.) Its methods include - Edge detection, Thresholding, Watershed and gradient.

Question 29

Explain the process of Edge Detection.

Answer 29

Edges and boundaries often show sharp adjustments in intensity at the region of their boundaries. This is used to define the edges. Local features such as colour and machine learning (to recognise objects) are also used.

Question 30

Explain the process of thresholding.

Answer 30

From a greyscale image thresholding can be used to create binary images.

Question 31

Explain the process of watershed.

Answer 31

Goes along axis to find peaks and troughs (in intensity), fills from one peak to the next to identify objects (fill function in paint makes use of this).Also names objects with an identification number.

Question 32

Explain the process of gradient.

Answer 32

Changes the intensity values to high and low to produce a gradient.

Question 33

Name techniques of data cleaning used in image processing.

Answer 33

Spatial Filtering - is an image operation where each pixel volume is changed by a function of the intensities of pixels in the surrounding neighbourhood. Temporal Filtering - used in video to blur out the sequence evolution to smooth out the temporal variation.

Question 34

Name ‘types’ of noise and define noise.

Answer 34

Noise - unwanted variations in a signal that result from imperfection in the transmission. Types - Electronic, Thermal and Speckle

Question 35

Give descriptions of the following types of Noise:Electronic, Thermal and Speckle.

Answer 35

Electronic - Noise emitted from electronic sources. Thermal - Electrical fluctuations resulting from the random thermal motion of electronics (dark current).Speckle (ultrasound ) - Granular noise created due to interference between the returning wave and the aperture.

Question 36

Give techniques for reducing noise.

Answer 36

Filter out - (E.g. low pass) Subtract Dark Current - the electric current that flows through photosensitive devices then no photons are entering the device. Time dependency - some noise is time dependent so repeat data collection over time.