Med Imaging Lecture 1- Study Guide

The more x rays that reach an area of the film….

The more x rays that reach an area of the film….

the darker that area will be

How will an object appear that is very dense?

It will appear white since less x rays will reach the film

How will an object appear if it is less dense?

It will appear black since more x rays are reaching the film

What color are shadows on x ray films?

White

What color are exposed areas on film?

Black

What is the order of the 5 basic radiographic densities in order of increasing brightness?

1.Gas/air—> Air density, lungs are dark
2.Fat
3.Fluid —> Heart appears lighter than lungs due to containing fluid aka blood
4.Bone —> Composed of calcium and are brighter
5.Metal

What is the affect of the thickness of a body part on image quality?

Thicker body parts absorb more x rays, leads to less x-ray penetration and brighter image

When imaging the chest, which will appear darker: lungs or the ribs and spine?

Lungs, the thinner structure, will appear darker
*Contrast helps in identifying abnormalities like fractures or tumors

What is the effect of motion on image quality?

It can cause blurring, reducing image sharpness and detail.

What is the effect of magnification on image quality?

Image can appear larger or less sharp depending how close the object is to the x ray source and detector.

What is the effect of distortion on image quality?

Image can be stretched or skewed due to xray beam not being perpendicular to the object

What may happen in a lateral x ray of the spine if the patient is not positioned correctly?

Vertebrae may appear elongated or compressed

What are the techniques and clinical uses of CT?

Techniques—> spiral Ct, multi slice CT
Clinical uses —> trauma, cancer, internal organ eval

What are the advantages and limitations of CT?

High resolution images, quick scanning, higher radiation dose

What is the scanning process of CT?

1.Pt lies on a table and slides into a large, doughnut shaped machine (gantry)
2.X ray tube inside gantry rotates around you, sending out narrow beams of xrays through your body

How are images created with CTs?

1.As the xray passes, they are detected by digital x ray detectors on opposite side of body
2.Detectors send data to a computer which processes it to create cross sectional images/slices of the body
3.Slices can be viewed individually or combined to form a 3D image

What types of contrast agents are used in CTs?

Iodine based, barium based, gadolinium

What type of imaging uses radioactive tracers to visualize physiological processes?

Nuclear imagine (PET, SPECT)

What are radioisotopes used for nuclear imaging?

Technetium-99m, Fluorine-18

Which type of imaging uses magnetic fields and radio waves to create detailed images?

MRI

What are characteristics of T1 weighted images in MRI?

-highlights fatty tissues
-Fat appears bright while fluid (CSF) appears dark
-Visualizes fat containing tissues and bone marrow

Why do water and fluids appear dark?

They have longer T1 relaxation times

What is used to disturb the alignment of protons in the body’s tissues?

Radiofrequency pulse

What is the time it takes for protons to realign with the magnetic field after the pulse?

Relaxation Time

What are characteristics of T2 weighted images?

-highlight fat and water are white
-edema, inflammation, tumors
-increased water content

Which type of MRI highlights how long it takes for hydrogen atoms in those tissues to lose their energy after being disturbed by a radio wave?

T2 weighted

What is T2 relaxation time?

Time it takes for hydrogen atoms to lose their energy and stop spinning in sync after being hit by a radio wave

Why do fluids or areas with swelling appear bright?

They take longer to lose their energy

What is repetition time (TR)?

Time between each radio wave pulse
*long TR (over 2000ms) ensures that the differences in energy loss times (T2) are more noticeable

What is Echo time (TE)?

Time between radio wave pulse and when the signal is captured
*A longer TE (60-120 ms) helps capture the differences in how quickly tissues lose their energy

Which type of weighted image shows Fat as bright, and water as dark?

T1

Which type of weighted image shows fat and water as bright?

T2

Which type of weighted image uses short repetition time and echo time?

T1

Which type of weighted image is used for pathological detection?

T2

Which type of weighted image uses long TR and TE?

T2

What equipment and techniques are used for MRI?

Magnet and coils
Functional MRI and diffusion MRI
Used for neurology, MSK
**Watch out for metal implants and pacemakers

Which type of imaging uses high frequency sound waves to create images and has echoes reflect from tissues to form images?

Diagnostic Ultrasound

What is the equipment and techniques used for diagnostic ultrasound?

Transducers, ultrasound
-Doppler ultrasound, 3D ultrasound
Obstetrics, cardio
**Non-ionizing radiation