Module 1: Principles of medical imaging (P2)

What is ultrasound?

USS uses high frequency sound waves to generate images. Once they are transmitted into the body, sound waves are reflected back as they encounter tissues of different densities at different depths.

How is ultrasound detected?

Reflected waves are detected by the transducer on the probe and represented on the screen.

What scientific principle underlies the production of sound waves in ultrasound?

The piezoelectric effect.

What are the common types of transducers used in ultrasound?

Linear, curvilinear, and phased array with space impacting field of view and freqeuncy of sound waves.

What does B mode imaging produce?

Classic 2D images. There is also A mode, M mode and Doppler.

What does the orientation marker on an ultrasound image indicate?

It corresponds to the indicator on the probe (held on R-side of patient) and helps clinicians orient the image.

How is echogenicity categorized in ultrasound imaging?

Hyperechoic (white)

Hypoechoic (grey)

Anechoic (black)

What is hyperechoic ultrasound imaging?

Structures that return greater echoes of sound waves appear white (bones, fat and stones)

What is hypoechoic ultrasound imaging?

Structures the return weaker echoes of sound waves appear grey (cartilage and muscle)

What is anechoic ultrasound imaging?

Structure that don't result echoes appear black (fluid masses)

What is the significance of echocardiography in medical imaging?

It assesses ventricular dimensions and performance, including ejection fraction.

What is magnetic resonance imaging?

These machines are giant magnets that temporarily manipulate how the hydrogen protons within the human body spin to create very detailed images

What is the basis of MRI technology?

The human body if 70% water with two hydrogens atoms per water molecule. When exposed to a strong magnetic field, the H+ protons realign their axis.

How is radio frequency used in MRI?

Hydrogen-specific radio frequency is directed onto the body. The proton absorb this energy to spin and then the newly released energy from when they slowly return to their natural alignment is detected to generate images.

What is the importance of radio frequency in MRI?

The number and gradiaent of radio frequency pulses delivered impacts the final image. Specialised sequences are used for different tissues.

What are T1 weighted images best used for?

Evaluating anatomical structures.

What are T2 weighted imaging best used for?

Water and fluid, particularly in cases of edema.

What disease processes can lead to oedema?

Inflammation

Trauma

Tumours

Strokes

How is fluid seen in T1 vs T2 weighted images?

T1 - Low intensity (black)

T2 - High intensity (white)

How is muscle seen in T1 vs T2 weighted images?

T1 - Intermediate (grey)

T2 - Intermediate (grey)

How is fat seen in T1 vs T2 weighted images?

T1 - High intensity (white)

T2 - High intensity (white)

How is grey matter seen in T1 vs T2 weighted images?

T1 - Intermediate (grey)

T2 - Intermediate (grey)

How is white matter seen in T1 vs T2 weighted images?

T1 - High intensity (white-ish)

T2 - Low intensity (dark-ish)

What is the primary safety concern when using MRI machines?

The presence of ferromagnetic materials.

What are other considerations for MRIs?

MRi machine is loud and requires patients to lay flat for an extended period of time in a small tunnel. Sedative or analgesia use is common.