Lecture - Advanced Imaging

What does a CT scan create?

Radiographs using thousands of fast projections taken with a radiograph tube that spins around the patient.

How are CT scan projections organized?

As a series of 2D images.

Why can no one be in the room during a CT scan?

Due to high levels of constant radiation.

Why do patients need to be sedated or under general anesthesia for a CT scan?

To keep them still for accurate imaging.

Who can CT images be sent to for further evaluation?

A radiologist.

What are the advantages of a CT scan?

It distinguishes between different soft tissues and can visualize vasculature and organ systems with a radiopaque contrast medium.

What are some uses for CT scans?

Diagnosing nasal disease, mass assessment, orthopedic disease (FCP, OCD), abnormalities, and pre-surgical planning.

What is the focal plane in a CT scan?

The section or layer at which minimal blurring occurs.

What is the Region of Interest (ROI) in a CT scan?

A fixed point in the anatomy of the patient that is in focus.

Why must structures above and below the ROI be blurred in a CT scan?

To make the ROI stand out in focus.

How does a CT scanner process images?

An x-ray tube emits a fan-shaped beam, rotates 360 degrees around the patient, and x-ray detectors collect the attenuated beam.

What happens after x-ray photons reach the detectors in a CT scan?

They are converted into an electrical signal, processed by an analog-to-digital converter, and reconstructed into images by a computer.

Why does the CT table move forward in increments?

To acquire multiple slices for a complete examination.

How does a CT scanner display images?

The computer reconstructs and displays them so each "slice" is in perfect focus.

What affects how a CT image is displayed?

CT number, window, and level.

What do high CT numbers represent, and how do they appear?

More radiopaque structures (e.g., bone, metal), appearing white.

What do low CT numbers represent, and how do they appear?

More radiolucent structures (e.g., air, fat), appearing black.

What do intermediate CT numbers represent, and how do they appear?

Soft tissues and fluids, appearing in shades of grey.

What does the window setting in a CT scan control?

The number of shades of grey (contrast).

What does a wide window in a CT scan do?

Increases the number of grey shades, lowering contrast (useful for soft tissue imaging).

What does a narrow window in a CT scan do?

Decreases the number of grey shades, increasing contrast (useful for distinguishing similar structures).

What does the level setting in a CT scan control?

The midpoint of the range of greys (brightness).

What does a lower level in a CT scan do?

Makes the image appear darker (better for air-filled structures).

What does a higher level in a CT scan do?

Makes the image appear brighter (better for dense structures like bone).

What settings are used for a lung CT scan?

Low level and wide window to see subtle soft tissue differences.

What settings are used for a bone CT scan?

High level and narrow window to enhance detail in dense bone structures.

What are some general characteristics of MRI?

Provides almost real-time images, is slower than CT, and is good for visualizing soft tissues, fluids, and pathological conditions.

What is MRI preferred for assessing?

Neurological conditions, spinal cord injuries, and tracing blood flow.

How does an MRI generate images?

Protons in tissues or liquids temporarily respond to a radio frequency, generating tissue-specific signals.

How do hydrogen atoms respond to an MRI's radio frequency?

They resonate into a higher energy state, change their magnetization angle, and wobble together.

What happens when the MRI's radio frequency is removed?

Molecules return to their normal energy state and emit a signal used to create an image.

Why are MRI magnets dangerous?

They can cause projectile effects and require personnel to be properly trained.

What is the projectile effect in MRI?

The launching of a metallic object into the magnet by magnetic force.

What must be checked before entering an MRI room?

That individuals have no unsafe implants or loose metal objects.

What are signal intensities in MRI?

The various shades of grey seen in an image.

What does high signal intensity in an MRI mean?

The structure appears bright/white.

What does low signal intensity in an MRI mean?

The structure appears in darker shades of grey.

What is a T1 MRI scan used for?

Imaging the brain and spinal cord due to high lipid content.

What appears bright in a T1 MRI scan?

Fat and bone marrow.

What appears dark in a T1 MRI scan?

Fluids, solid masses, and cortical bone.

What is a T2 MRI scan used for?

Visualizing fluid.

What appears bright in a T2 MRI scan?

Flowing blood and cysts.

What appears grey in a T2 MRI scan?

Pooling blood and fat.

Why is contrast used in MRI?

To highlight infections, tumors, and vascular disease.

What contrast agent is used in MRI?

Gadolinium.

Which MRI scan type shows contrast enhancement?

T1 scans.