Medical Imaging Using X-rays Flashcards

Comprehensive practice flashcards covering the principles of 2-D x-rays, Digital Subtraction Angiography (DSA), and Computerised Tomography (CT) based on the medical imaging lecture.

What are traditional 2-D x-rays commonly used to detect or diagnose?

Bone fractures or health conditions like pneumonia.

How is the attenuation of x-ray beams in air described?

Negligible.

Why is the attenuation of x-ray beams in the lungs described as weak?

Due to low density.

Why is the attenuation of x-ray beams in bone described as significant?

Due to relatively high density and the atomic mass number of $Ca$ (high $Z$ number).

How does the x-ray attenuation of soft tissue compare to other substances?

It is similar to water.

At what energy level is the contrast between bone and soft tissue greater?

At lower energies.

What products are used to make body cavities visible in x-ray imaging?

Contrast products such as iodine and barium.

What does the acronym DSA stand for in medical imaging?

Digital Subtraction Angiography.

What is the primary value of Digital Subtraction Angiography (DSA)?

Studying blood supply to various organs.

What is the first step in performing Digital Subtraction Angiography (DSA)?

A normal x-ray picture is taken of the area.

What is introduced into the bloodstream during the Digital Subtraction Angiography (DSA) process?

Contrast media, typically iodine-based.

Why are contrast media in DSA chosen such that their K-edge matches the x-ray energies used?

To optimise absorption characteristics.

How do blood vessels appear in x-ray imaging after contrast media is introduced?

They become highly absorbing and hence highly visible.

How is the detailed image of blood vessel structure revealed in DSA?

Two digitized images are digitally subtracted from each other to remove underlying anatomical features.

What is the definition of tomography based on the lecture principles?

Reconstructing the structure of an object from a series of x-ray projections taken uniformly around it.

How many units of incident radiation and transmitted radiation were used in the first tomography example?

$100$ units of incident radiation and $50$ units of transmitted radiation.

How many units of transmitted radiation were in the second tomography example?

$20$ units.

What is another name for Computerised Tomography (CT)?

Computer Axial Tomography (CAT).

In CT, how is a thin pencil beam of x-rays passed through tissue?

From many different directions so that all beams have a common crossing point.

What yields detailed information on absorption within a 'common volume' in CT?

A study of the transmission data for all beams passing through that volume.

What does 'lac' stand for in the context of CT beam intensity?

Linear attenuation coefficient.

Which law describes the cumulative attenuation along the path of an x-ray beam?

The Lambert-Beer Law.

How does a CT computer handle the linear attenuation coefficients (lacs)?

They are mathematically manipulated using fast microprocessors to calculate absorption as a function of position.

What does each element of the computer-constructed $3\text{-d}$ array in CT correspond to?

A specific location within the patient under assessment.

What does the numerical value assigned to each element in a CT array represent?

The calculated absorption at that location.

Explain the phrase 'the computer paints by numbers' regarding CT reconstruction.

A colour scheme or greyscale is assigned to particular values of absorption to construct an image.

What types of tissues are modern CT scanners capable of resolving?

Soft tissue, muscle, blood, malignancies, and bones.

How are projections obtained in CT image formation?

By passing thin beams of x-rays through the object and measuring absorption using detectors.

In the illustrated example, what do the measured absorption values (ray-sums) represent?

The number of blocks that the beam passes through in each projection.

How are the absorption values at each crossover point determined during reconstruction?

Values for overlapping projections are added to represent the total absorption at that point.

What significantly affects the resolution of a reconstructed CT image?

The choice of colour code and the range of values assigned to specific colours.

How do CT scanners obtain many projections along the length of the body?

By scanning in a spiral fashion.

What is the name of the stored data containing x-ray projections?

A sinogram.

Where do modern CT machines house the x-ray sources and detectors?

Inside a circular 'gantry'.

Where is the control panel for setting radiological parameters usually located?

Outside the CT room.

What is reconstructed from the digitally recorded $2\text{-d}$ 'slice images' in modern CT?

$3\text{-d}$ images.

What does the digital storage of CT information allow users to do with the image?

It can be manipulated, for example, rotated.

What does the acronym CAS stand for in the context of surgical planning?

Computer Assisted Surgery.

How is Computer Assisted Surgery (CAS) used in trauma repair?

To design complex prostheses for corrective repair.

What specific injury was showcased in the detailed $3\text{-d}$ CT image prior to surgical repair?

A complex facial fracture.

What technique is used to improve image clarify in CT reconstruction?

The selection of an appropriate colour code or scale.

What type of imaging was used to compare with the CT image of a cadaver's chest?

Cryosection image.

How many bits of information were used in the tomography examples to construct an image mentally?

4 bits of information.

What is a key principle of CT image reconstruction involving an empty array?

An empty array is set up in the computer which is then filled with values from the sinogram.