Medical Imaging Fundamentals

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Questions and Answers

What is the primary effect of doubling the distance from the source of radiation?

Exposure increases by 2x

Exposure decreases by 4x (correct)

Exposure remains constant

Exposure increases by 4x

What is the purpose of using radiopaque fluids like iodine or barium in medical imaging?

To reduce the risk of radiation exposure

To visualize the morphology of the GI tract

To assess the motility of the thorax

To enhance the visibility of luminal or vascular organs (correct)

What is the primary advantage of fluoroscopy over other imaging techniques?

It provides high-resolution images of the thorax

It enables real-time imaging of the GI tract (correct)

It is a non-invasive imaging technique

It uses a low dose of radiation

How are CT images typically viewed?

As if you are standing at the patient's feet Signup and view all the answers

What is the primary limitation of MRI scans?

It is contraindicated in patients with metal implants Signup and view all the answers

What is the primary mechanism of action of MRI scans?

It uses magnets and radio waves to create detailed images Signup and view all the answers

What is the primary difference between CT and MRI scans?

CT scans use X-rays, while MRI scans use magnets and radio waves Signup and view all the answers

What is the primary application of fluoroscopy in medical imaging?

Assessing the motility of the GI tract Signup and view all the answers

What is the primary function of X-rays in conventional radiology?

To pass through a patient onto a detector or film Signup and view all the answers

What is the orientation of the radiograph when viewed by a radiologist?

As if the patient is facing you, with feet and hands appearing as if you are looking at your own Signup and view all the answers

What color appears on the X-ray image when few X-rays reach the detector?

White Signup and view all the answers

What is the relationship between the intensity of the X-ray beam and the distance from the source?

The intensity of the X-ray beam decreases with the square of the distance from the source Signup and view all the answers

What is the primary characteristic of X-rays that can cause harm to living tissues?

Higher energy to ionize atoms and disrupt molecular bonds Signup and view all the answers

What type of tissue appears as dark grey on the X-ray image?

Fat Signup and view all the answers

What is the term used to describe dense tissues that absorb/reflect more X-rays?

Radiopaque Signup and view all the answers

What type of tissue appears as black on the X-ray image?

Air Signup and view all the answers

What is the primary reason why people with metal objects inside their body should not undergo an MRI?

Risk of injury Signup and view all the answers

What is the main advantage of Ultrasonography/Ultrasound?

It is safe during pregnancy and for children Signup and view all the answers

What is the purpose of the radioactive compound in Nuclear Medicine Imaging?

To attach to a substance that a specific organ absorbs Signup and view all the answers

Why is Ultrasound not suitable for imaging the adult brain?

Because bones reflect most ultrasound waves Signup and view all the answers

What is the purpose of the gel used in Ultrasound?

To get better images and avoid interference Signup and view all the answers

What is the principle behind Doppler Ultrasound?

Measuring the frequency shifts of reflected ultrasound waves Signup and view all the answers

What is the purpose of a full bladder in abdominal Ultrasound?

To act as a 'window' to transmit sound through Signup and view all the answers

What is the main difference between MRI and Nuclear Medicine Imaging?

Nuclear Medicine Imaging uses radiation, while MRI does not Signup and view all the answers

Study Notes

Radiation and Imaging

Doubling the distance from the X-ray source reduces exposure by 4 times.
Closer to the light source, the image is larger, and closer to the wall, the image is sharper.

Contrast Media

Radiopaque fluids like iodine and barium are used in medical imaging.
They are administered through intravenous (IV), oral routes, or catheter into various cavities.
These fluids enable the study of luminal or vascular organs.

Fluoroscopy

Fluoroscopy is a 2D imaging technique using continuously emitted X-rays for real-time imaging.
It is often used to assess the GI Tract.
Provides insight into the morphology and motility of these organs.

Computed Tomography (CT)

CT is an imaging technique using X-rays to create tomographic images.
Patients lie supine on a scanner table and pass through the CT gantry (X-ray tube and detectors that rotate around the patient).
A computer uses X-ray projections to reconstruct images.

Viewing CT and MRI Images

CT images (and MRI) are viewed as if you are standing.
Axial: viewed from the supine position, with the patient's feet at the top.
Coronal: viewed from the front, facing the patient.
Sagittal: viewed from the patient's left side.

MRI Scans

MRI uses magnets and radio waves to create detailed cross-sectional images.
The machine generates a strong magnetic field that excites the nuclei of atoms in the body.
Radio waves temporarily disrupt this alignment, causing the nuclei to emit energy signals that vary in different tissues.
These signals are detected by a coil around the body.
MRI does not involve harmful radiation and is safe during pregnancy and for children.
People with metal objects inside their body should not have an MRI due to the risk of injury.

Ultrasonography/Ultrasound

Ultrasound uses ultrahigh frequency sounds that bounce off due to changes in density.
High density = brighter image.
Bone reflects nearly all ultrasound waves, making it unsuitable for CNS imaging.
Ultrasound is operator-dependent.
It cannot be used on the adult brain or lungs due to the presence of air.
Gel is used to get better images and avoid interference.
Doppler ultrasound measures the speed of blood flow using frequency shifts.
For abdominal ultrasounds, having a full bladder helps by acting like a "window" and transmits sound through.

Nuclear Medicine Imaging

Nuclear Medicine Imaging (NMI) reveals information about the spread and concentration of small amounts of radioactive substances in the body.
A radioactive compound is attached to a substance that a specific organ absorbs.
A detector displays where the radiotracer is in the body.
NMI is used for diagnosis and to treat cancer, where radiotracers gather in tumors and emit particles that kill cancer cells.

Conventional Radiology (Plain Radiographs)

Radiography uses X-rays for digital 2D image creation.
X-ray images (radiographs) are obtained by passing X-rays through a patient onto a detector or film.
Posterior Anterior (PA) projection involves the X-ray entering from the patient's posterior aspect and exiting anteriorly to reach the detector/film.
AP radiograph is the opposite of PA.
Radiographs are typically viewed with a standard orientation, as if the patient is facing you, with feet and hands appearing as if you are looking at your own.

Conventional Radiology - Radiopacity and Radiolucency

Dense tissues absorb/reflect more X-rays, making them "radiopaque/radiosense" (bright area).
Less dense tissues are "radiolucent" (allow more X-rays to pass through).
Air appears black on the X-ray image.
Fat is depicted as dark grey.
Soft tissue appears as brighter grey.
Bone appears white.
Metal appears even whiter.

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Description

Test your understanding of medical imaging concepts, including radiation, contrast media, and fluoroscopy.