Thoracic Protocols Flashcards by Gracie Costello

What is the challenge of thoracic imaging?

Motion due to heart and vascular structures

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How is motion due to heart and vascular structures overcome in thoracic imaging?

MDCT
DSCT
ECG Synchronization

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How does DSCT help with the reduction of motion?

Improves temporal resolution (speed of acquisition is increased)

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How does ECG synchronization help with motion?

Synchronized to the rhythm of the heart

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T/F
Most thoracic imaging scans are performed supine

True
*thoracic done supine and prone for COPD, HRCT

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Why are the arms raised above the head for thoracic imaging?

Eliminates out of field artifacts

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Why are short scan times used for thoracic imaging?

To reduce motion

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Why is a single breath hold necessary for thoracic scanning?

Eliminates misregistration

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T/F
The thorax has high intrinsic contrast

True
*pulmonary vessels and ribs have different attenuation values compared to the air filled lung
*mediastinal vessels and lymph nodes are surrounded by enough fat to be identified

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T/F
IV contrast is not necessary for all thoracic indications

True

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T/F
Due to high subject contrast nature of the thorax, contrast injection is not always warranted, unless requested by the radiologist

True

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Pulmonary nodules, lung disease, emphysema, fibrosis

Without contrast
*most common

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To highlight vascular structures (lymph nodes)

With contrast

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Contrast given to highlight the esophagus and gastroesophageal junction (GE)

Oral contrast

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What is required for general scanning of the airways?

Thin slice acquisition
-1.25mm or less

Single breath hold, fast scan

Optimal spatial resolution

Post processing techniques
-MPR
-MIP/MinIP *most used
-3D
-volume rendering

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-voxels with the highest value is included
-those with the lowest are ignored
bone and contrast structures are well demonstrated

Maximum intensity projection
MIP

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-displays voxels with the minimum values
useful for demonstrating the bronchial tree

Minimum intensity projection
MinIP

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-3D semitransparent representation of the imaged structure
-all voxels contribute to the image
-relationship between multiple tissues are shown

Volume rendering

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What is the scanning parameters for a routine chest

-above apices
-below costophrenic angles

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What change is made to the scan parameter for routine chest If there is a known or suspected lung cancer?

End just below the adrenal glands
(Start above apices)

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T/F
For imaging of the airways, oral or IV contrast is normally not required, an exception might be an airway tumor

True

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T/F
General CT of the airway is routinely done in both inspiration and/or expiration

True

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What is a general airway CT most commonly used to look for?

Narrowing
*epiglottitis, cystic fibrosis, asthma, allergic reaction, after ET tube removal

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What is done to slice thickness for MIP?

Increase slice thickness

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What are the two protocols for high resolution CT? HRCT

ILD - interstitial lung disease OLD - obstructive lung disease

Used to evaluate the lung parenchyma in patients with known or suspected diffuse lung disease *fibrosis, edema…

High resolution CT HRCT

What is diffuse lung disease?

Scarring (fibrosis) of the lungs

T/F HRCT can be scanned either axially or helically (both protocols will include more than 1 series of scans)

True *supine - Insp/exp *prone - Insp

T/F For HRCT, the helical scan will not be scanned prone

True *axial will scan supine Insp/exp and prone Insp

What is the goal of inspiration scans for HRCT?

To maximize the contrast between aerated airspace and high attenuation structures, such as the interstitial tissue

What is the goal of expiration for HRCT?

To see areas that do not get smaller or empty *done for air trapping, bronchiolitis

What is expiration HRCT done for?

Air trapping Bronchiolitis *when scanning in expiration lung cavity will be smaller, if not seen smaller, pathology may be present

How is spatial resolution optimized for HRCT?

-the use of edge enhancement algorithm (bone) -DFOV just large enough to include the lungs

Why is scanning the apices important?

Tuberculosis (secondary?)

What is the main modality of choice for the diagnosis of pulmonary embolism?

CT *improved image quality *thinner slices *faster acquisition for dyspneic patients

Clot within the vascular system -could be life saving when bleeding -could be life threatening if blocking O2 access to vital organs

Thrombosis

What are most pulmonary embolisms cause by?

Thrombi originating in the lower extremities (DVT) *can also be cause by tumors invading the circulatory system, amniotic fluid, air, fat, bone marrow, and foreign substance

T/F Pulmonary embolisms can present with no signs, or nonspecific signs such as dyspnea, to massive chest pain

True *many clinical problems can simulate a PE *timely accurate diagnosis of PE is crucial

What screening blood test is used for PE?

D-dimer *used for screening, but will not confirm *further tests are required if D-dimer is elevated (such as CT)

Can detect PE and/or any other thoracic pathologies that may explain the patients symptoms

CTA PE *if a dissection or pulmonary embolism is in question, dissection protocol should be performed

What are the disadvantages of CTA PE?

-visualization of smaller arteries can be affected by problems with technique or suboptimal vessel pacification -breathing motion affects the smaller arteries much more than the bigger central arteries -head to toes scanning will cause more breathing artifacts at the base of the lung than the apices for patients who can’t hold their breath for the scan duration *toe to head scanning common

What are factors that affect maximum opacification in CTA PE?

-age -cardiac output -lung disease -site of IV catheter -experience of tech

T/F The use of saline after and injection of contrast for CTA PE eliminates beam hardening artifacts which may obscure PE in small vessels

True

When scanning a large patient and pregnant women for a CTA PE, what phase or respiration is required?

Expiration

What patients are cardiac CTs performed on?

Patients with high susceptibility for coronary artery disease

T/F Cardiac CT must have high temporal resolution in order to increase the spatial resolution

True

What are 2 strategies used to decrease heart motion artifacts in cardiac CT?

Use of beta blockers Cardiac gating

Used to lower heart beat to <65-70 bpm and to make rhythm more regular

B-blockers

What is the most commonly used b-blocker?

Metropolol tartrate

-given sublingual to dilate coronary vessels -can also help prevent spasms which can mimic stenosis

Nitroglycerin

What are the disadvantages of prospective gating (step and shoot)?

-very sensitive to cardiac motion -image misregistration

-identifies the areas of lowest cardiac motion and acquires images only in those portions of the cardiac cycle

Prospective gating **lowers dose**

-images are acquired throughout the entire cardiac cycle -images are later reconstructed to create images in the desired cardiac cycle

Retrospective gating **increased dose**

What type of contrast is used for cardiac CT?

Low osmolar or nonionic Concentration: 300-400mg/mL

What is the injection rate of contrast for cardiac CT?

Rapid 3-6mL/s *increased risk of extravasation

What volume of contrast is used for cardiac CT?

70-150mL

What is the target enhancement with contrast for cardiac CT?

200-300 HU

T/F For cardiac CT, optimal injection time can be achieved by using a timing blood or bolus tracking

True

Can determine the location and extent of calcified plaques in the coronary arteries

Calcium scoring CT

T/F Calcium in the coronary arteries is a marker of coronary artery disease CAD

True *May present with no symptoms

How is a calcium scoring CT scored?

Based on HU of calicum

How are calcium scoring CT results expressed?

Negative exam Positive exam

Calcium scoring No calcium, and low chance of CAD in the next 2-5 years

Negative exam

Calcium scoring CAD is present, even if no symptoms are present

Positive exam

Why would a calcium scoring test not be done?

If patient has a stent *stent will artificially increase the score

Calcium score 0

No evidence of plaque

Calcium score 1-10

Minimal plaque

Calcium score 11-100

Mild plaque

Calcium score 101-400

Moderate plaque

Calcium score More than 400

Extensive plaque

Thoracic Protocols Flashcards

(70 cards)