MRI Pathology PART I Principles of Imaging in Computed Tomography and Magnetic Resonance Imaging & PART II Contrast Media

- CT AND MRI CONTRAST AGENTS -PRINCIPLES OF IMAGING IN COMPUTED TOMOGRAPHY AND MAGNETIC RESONANCE IMAGING

When did Wilhelm Conrad Roentgen discover the x‑ray?

November 8, 1895

What was the first major breakthrough in radiology after the discovery of x‑ray?

Computed tomography (CT) in the early 1970s

What was the second major breakthrough in radiology after CT?

Magnetic resonance imaging (MRI) in the early 1980s

What do CT and MRI have in common regarding their impact on radiology?

Both revolutionized how we visualize the inside of the patient’s body

What happens to a finely collimated x‑ray beam in CT?

It is directed at the patient as the x‑ray tube rotates around them

What happens to x‑rays as they interact with tissues in CT?

Some are attenuated and some are transmitted

What is the purpose of CT detectors?

Measure transmitted radiation through the patient

What do CT detectors convert transmitted radiation into?

An electronic signal

What does the CT computer do with detector signals?

Performs mathematical calculations and reconstructs the image

What do CT numerical values represent?

Average density of tissue in each pixel/voxel

What are CT numerical values called?

Hounsfield numbers, Hounsfield units (HU), or CT numbers

What is the approximate HU range in CT?

→ −1000 (air) to +3000 (dense bone/tooth enamel)

What is the Hounsfield number assigned to water?

0

What does a radiologist look for when diagnosing disease on CT?

Changes in normal HU density, abnormal masses, or altered/lost anatomy

Which patients benefit from CT due to speed and accessibility?

Trauma, suspected stroke, acutely ill, MRI‑contraindicated, or needing bone detail

What technological development in the early 1990s improved CT imaging?

Helical (spiral) CT

What advancement in the mid‑1990s further improved CT capabilities?

Multi‑slice imaging

What does volumetric CT imaging allow?

Rapid acquisition and reformatted images in any plane

What is a disadvantage of CT?

Exposure to radiation

What is another disadvantage of CT?

Possible reaction to iodinated contrast

What is a limitation of CT compared to MRI?

Loss of soft‑tissue contrast

What does MRI use to generate images?

Strong magnetic field, gradient fields, RF signal, and RF coils

What frequency is the Larmor frequency of hydrogen?

42.58 MHz/T

What do gradient magnetic fields control in MRI?

Slice selection, phase encoding, frequency encoding

How do hydrogen protons align in the magnetic field?

Parallel or antiparallel to B₀

What happens when the RF signal is turned on?

Protons are flipped away from the parallel axis

What happens when the RF signal is turned off?

Protons relax back to parallel alignment

When is MRI signal received by the coils?

During proton relaxation

How is an MRI image acquired?

Repeated cycles of RF excitation, relaxation, and signal detection

What are the three main groups of MRI pulse sequences?

Proton density, T1‑weighted, T2‑weighted

Why are different MRI pulse sequences used?

They demonstrate anatomy differently and help differentiate normal vs. abnormal structures

What TR and TE values characterize a T1‑weighted sequence?

Short TR and short TE

What substances appear bright on T1‑weighted images?

Fat, acute hemorrhage, slow‑flowing blood

What structures appear dark on T1‑weighted images?

CSF and simple cysts

How do most pathologic processes appear on T1‑weighted images?

Low signal (dark)

What TR and TE values characterize a proton‑density‑weighted image?

Long TR and short TE

What does brightness represent on a proton‑density‑weighted image?

High concentration of hydrogen protons

What does darkness represent on a proton‑density‑weighted image?

Low concentration of hydrogen protons

What TR and TE values characterize a T2‑weighted sequence?

Long TR and long TE

What substances appear bright on T2‑weighted images?

CSF, simple cysts, edema, tumors

How do fat and muscle appear on T2‑weighted images?

Low signal (dark)

How do many pathologic conditions appear on T2‑weighted images?

High signal (bright)

What is one major advantage of MRI?

It acquires patient information without ionizing radiation

What type of contrast does MRI excel at producing?

Excellent soft‑tissue contrast

In which planes can MRI acquire images?

Axial, sagittal, coronal, oblique

How does bone affect MRI image quality?

It does not affect image quality

What is a primary disadvantage of MRI?

Contraindications that may harm patients or staff

What is another disadvantage of MRI compared to CT?

Longer scan times

What is a third disadvantage of MRI?

Higher cost

What poses the greatest harmful effects to biomedical implants in MRI?

Magnetic field, gradient fields, and RF energy

Who must be screened before entering the MRI environment?

Everyone: patients, family, staff, maintenance workers

What types of implants may be contraindications for MRI?

Electrically, magnetically, or mechanically activated devices

What risks do contraindicated implants pose in MRI?

Movement/torque, overheating, artifact, or functional damage

What type of magnet is most commonly used in MRI?

Superconductive magnet

What is always true about the MRI magnetic field?

It is always on

What can ferromagnetic materials become in the MRI environment?

Dangerous projectiles

Why must CT and MRI technologists understand contrast administration?

Many exams require contrast, and safe use depends on proper venipuncture and dosing

What is the first thing a technologist must determine before administering contrast?

The specific contrast agent to be used

What is the second requirement for safe contrast administration?

The correct amount of contrast to be used

What is the third requirement for safe contrast administration?

The appropriate injection site

What is the fourth requirement for safe contrast administration?

The correct injection rate

What is the fifth requirement for safe contrast administration?

The appropriate gauge of the IV needle

What should be documented after contrast administration?

All venipuncture details, contrast administration details, and patient outcome

Why is documentation important after contrast administration?

Ensures patient safety and provides a complete medical record

What should technologists review before using CT or MRI contrast agents?

Main safety considerations related to each contrast type

What type of contrast agents are used extensively in CT?

Water‑soluble, iodine‑based contrast agents

Why have low‑osmolar contrast agents replaced high‑osmolar ionic agents?

Lower risk of adverse reactions

What is the adverse reaction rate for ionic contrast agents?

5% to 12%

What is the adverse reaction rate for nonionic, low‑osmolality contrast agents?

1% to 3%

What type of CT contrast reaction is most common?

Mild reactions

How long should patients with mild reactions be observed?

30 minutes

Which of the following is a mild contrast reaction?

Nausea/vomiting

Which symptom is considered a mild reaction?

Urticaria/pruritis

Which of the following is a mild reaction?

Itchy/scratchy throat

Which of the following is a mild reaction?

Feeling warm/chills

Which of the following is a mild reaction?

Headache/dizziness/anxiety/altered taste

What characterizes moderate contrast reactions?

Not life‑threatening but often require treatment

Which is a moderate reaction?

Diffuse urticaria/pruritis

Which is a moderate reaction?

Diffuse erythema with stable vitals

Which is a moderate reaction?

Facial edema without dyspnea

Which is a moderate reaction?

Throat tightness/hoarseness without dyspnea

Which is a moderate reaction?

Wheezing/bronchospasm with mild or no hypoxia

Which is a moderate reaction?

Protracted nausea/vomiting

Which is a moderate reaction?

Isolated chest pain

Which is a moderate reaction?

Vasovagal reaction responsive to treatment

What medication is effective for symptomatic hives?

Benadryl

What treatment helps with bronchospasm?

Beta‑agonist inhaler

What medication is indicated for laryngeal spasm?

Epinephrine

What position is used for vasovagal reaction with hypotension?

Leg elevation (Trendelenburg)

When do severe contrast reactions typically occur?

Within the first 20 minutes after injection

Which is a severe contrast reaction?

Diffuse edema or facial edema with dyspnea

Which is a severe contrast reaction?

Diffuse erythema with hypotension

Which is a severe contrast reaction?

Laryngeal edema with stridor and/or hypoxia

Which is a severe contrast reaction?

Anaphylactic shock (hypotension with tachycardia)

Which is a severe contrast reaction?

Vasovagal reaction resistant to treatment

Which is a severe contrast reaction?

Arrhythmia

Which is a severe contrast reaction?

Convulsions or seizures

Which is a severe contrast reaction?

Hypertensive emergency

What can severe bronchospasm or severe laryngeal edema progress to?

Unconsciousness, seizures, hypotension, dysrhythmias, cardiac arrest

What immediate action is required for severe bronchospasm or laryngeal edema that progresses?

Immediate cardiopulmonary resuscitation