Exam questions

List the 7 basics steps of image production in CT

1. x-ray tube directs x-ray beam towards pt

2. x-ray beam is attenuated

3. remnant photons are collected by detector

4. detector creates electrical radiation readings

5. radiation reading converted to digital signal

6. raw digital signal is processed into digital images

7. digital image sent to monitor

What components are located within the scanner gantry

x-ray tube

pre-patient collimator (determines beam width)

detectors (collects photons, converts to electrical signal)

post-pt/detector collimators (protects from scatter)

high-volt gens (produces variable kvp/ma)

analog to digital converter

Formula for Beam width

detector rows X slice thickness

What are the four photon interactions in CT?

1. Transmission

2. Coherent scattering

3. Photoelectric absorption

4. Compton scattering

Which photon interactions are NON-ionizing?

• Transmission

• Coherent scattering

Which interactions are IONIZING?

• Photoelectric effect

• Compton scattering

What is transmission?

X-rays pass through the body with no interaction.

What happens in coherent scatter? what is the alternate word?

Photon is absorbed and immediately re-emitted.

Rayleigh scattering

What happens in photoelectric absorption?

Photon is completely absorbed by an electron.

What happens in Compton scattering?

Photon interacts with an electron and loses part of its energy.

what photon interaction is this

Photoelectric absorption

what photon interaction is this

Compton

what is overbeaming

The x-ray beam is widened so every detector gets equal x-ray exposure.

what is overranging

Extra radiation is used before and after the scan area so the computer has enough information to reconstruct accurate helical images.

abnormal levels of consciousness:

1. Alert: conscious have the ability to fully respond

2. lethargic: patient appears drowsy

   but can be aroused.

3. obtunded: patient is in a more depressed level

   of consciousness and may not easily be aroused

   from a state of confusion.

4. Stupor (semicomatose): describes a state of near unresponsiveness

5. coma: patient is completely unresponsive to stimuli

Normal body temperature

97.7° to 99.5°F

Pulse rate for adults and children

Adults: 60 to 100 bpm

children: 70 to 120 bpm

Normal respiration rate for adults/children

Adults: 12 to 20 breaths per minute

Children: 20 to 30 breaths per minute.

Normal systolic and diastolic reading

systolic = 100-120

diastolic = 60-80

Normal pulse oxi range

90% to 100%

What is the first phase of heart contraction?

Contraction of the right and left atria.

What happens when the atria contract?

Blood is pushed into the ventricles.

What is the second phase of heart contraction?

Contraction of the ventricles.

What happens when the ventricles contract?

Blood is pumped into the pulmonary arteries and the aorta.

What does the P wave represent?

Electrical activity (depolarization) of the right and left atria.

What does the QRS complex represent?

Electrical activity (depolarization) of the ventricles.

What cardiac phase occurs during the QRS complex?

Ventricular systole (ventricular contraction).

What is the ST segment?

The period when the ventricles are contracting but no electrical activity is flowing.

Where is the ST segment located?

Between the QRS complex and the T wave.

What does the ST segment normally look like?

A straight, level line.

What does the T wave represent?

Ventricular repolarization. The ventricles reset electrically and prepare for the next contraction.

Which EKG waveform represents atrial depolarization?

P wave.

Which waveform represents ventricular depolarization?

QRS complex.

Which waveform represents ventricular repolarization?

T wave.

Which part of the EKG shows ventricular contraction without electrical activity?

ST segment.

Which CT exams commonly use EKG gating?

Cardiac CT and coronary CT angiography (CTA).

what drug can be administered to cause dilation of the coronary vessels, improving their visualization.

sublingual nitroglycerine

Cardiac CT images are typically reconstructed from data acquired during what phase

diastolic phase.

Which lab values evaluate kidney function?

• BUN

• Creatinine

• GFR

Which lab values evaluate blood clotting?

• PT

• PTT

• INR

• Platelet count

What is the normal BUN range?

7–21 mg/dL

What is the normal creatinine range?

0.7–1.5 mg/dL

What is the normal GFR?

90–120 mL/min

What is the normal PT?

11–13.5 seconds

Why is a high PT a contraindication for interventional procedures?

increased risk of uncontrolled bleeding.

What is the normal PTT?

25–35 seconds

What is the normal platelet count?

150,000–400,000/µL

Pitch = 1

The table moves exactly the same distance as the beam width during one rotation.

What occurs when pitch = 1? how is image quality, dose and scan speed

No overlap and no gaps.

image quality = Moderate

dose = Moderate

scan speed = Moderate

What does a pitch greater than 1 mean?

The table moves farther than the beam width.

What occurs when pitch > 1? what happens to image quality, dose and scan speed?

Greater gaps no laps

image quality = decrease

dose = decrease

scan speed = increased

What does a pitch less than 1 mean?

The table moves less than the beam width.

What occurs when pitch < 1? what happens to image quality, dose and scan speed?

No gaps. Overlaps

image quality = Increases

dose = Increases

scan speed = Decreases

A technologist wants to lower patient dose. What pitch change should be made?

Increase pitch

A technologist wants faster acquisition. What pitch change should be made?

Increase pitch

A technologist wants maximum spatial resolution. What pitch change should be made?

Decrease pitch

What is the formula for pitch?

Pitch = Table Movement ÷ Beam Width

What is the formula for table movement?

Table Movement = Beam Width × Pitch

What is temporal resolution

The ability of a CT system to freeze motion and provide an image free of blurring.

WW & WL for displaying gray/white matter

WW 100, WL 35

WW & WL for displaying Hemorrhage/hematoma

WW 150, WL 75

WW & WL for displaying Acute ischemia

WW 25, WL 35

(variable, high-contrast windowing improves the CT visualization of acute stroke)

WW & WL for displaying Lung parenchyma

WW 1400, WL −450

WW & WL for displaying Mediastinum

WW 350, WL 40

What is the formula for calculating lower window limit?

WL - (WW ÷ 2)

What is the formula for calculating upper window limit?

WL + (WW ÷ 2)

Typical Abdomen Window?

WW 400
WL 40

Typical Bone Window?

WW 2500
WL 600

Typical Lung Window?

WW 1800
WL -600

WW increases. What happens?

Contrast decreases.

WW decreases. What happens?

Contrast increases.

WL increases. What happens?

Image becomes darker.

WL decreases. What happens?

Image becomes brighter.

what is An omental CT scan?

Scan of the abdomen focused on the omentum, a fatty layer of tissue inside the abdomen

What is the HU for air

-1000

What is the HU for lung

-700

What is the HU for fat

-50

What is the HU for CSF

+15

What is the HU for blood

+30 to +45

What is the HU for muscle

+40

What is the HU for bone

+1000

How does acquisition thickness affect spatial resolution?

Thinner acquisition thickness increases spatial resolution.

How should images be reconstructed to maximize spatial resolution?

Use the thinnest reconstruction slice thickness possible.

How does matrix size affect spatial resolution?

Larger matrix size increases spatial resolution.

Name three factors that affect image noise.

• mA

• kVp

• Patient size

How does increasing mA affect contrast resolution?

 It improves contrast resolution.

How does increasing kVp affect contrast resolution?

It improves contrast resolution.

How does thicker acquisition thickness affect contrast resolution?

It increases contrast resolution.

How does thicker reconstruction slice thickness affect contrast resolution?

It improves contrast resolution.

Which ROI measurement represents image noise?

Standard deviation.

Which reconstruction algorithm produces more image noise?

Bone (edge-enhancing) algorithm.

what is the green arrow pointing to

coracoid process

CT image quality is evaluated in terms of

spatial resolution and contrast resolution

the ______ data acquisition mode moves the bed through the CT gantry while the x-ray tube and detector array remain stationary

scout

list the phases of tissue enhancement after injection of contrast media

bolus, equilibrium, nonequilibrium

The _____ phase of liver enhancement is optimal for the evaluation of hypovascular lesions such as metastases that develop from primary tumors of the colon

portal venous

The falciform ligament extends from the liver to the

anterior abdominal wall and diaphragm