BODY CT PROTOCOL DESIGN


 
 Oral contrast: Usually not needed for chest protocols unless looking for esophageal leak, etc.
 
Lung cancer screening
 
Based on data from the National Lung Screening Trial (NLST), annual screening for lung cancer using low-dose chest CT is recommended for patients 55-74 years of age with a 30+ pack-year history.

1. Noncontrast, low-dose images of the chest
● Radiation dose is estimated to be 1.5 mSv, which is similar to the dose for a lumbar spine x-ray [1]. In comparison, the estimated dose for a standard chest CT is approximately 7 mSv.
● To minimize patient dose, a reduced mAs (CareDose reference mAs of 50; normally 150) is used with a low kVp (100; normally 100 or 120).

 
1. American College of Radiology and Radiological Society of North America. Patient Safety: Radiation Dose in X-Ray and CT Exams. Retrieved March 19, 2015 from http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_xray.
Lung disease
(e.g. pneumonia, ILD)
 For dyspneic patients, use Siemens Flash mode Siemens Flash mode: This high-pitch dual-source scanning technique reduces scan time and thus motion artifact, but cannot be used in larger patients due to limited field-of-view.
 to reduce respiratory motion artifact.

1. Noncontrast inspiratory phase images of the chest
● IV contrast is not routinedly needed to assess for infection or lung parenchymal disease.
2. Add noncontrast expiratory phase images of the chest in the following cases:
● To evaluate for air trapping:
○  Initial evaluation of interstitial lung disease
○  Post-lung transplant
○  Any inflammatory or constrictive bronchiolitis (e.g. hypersensitivity pneumonitis, toxic fume exposure)
● To evaluate for tracheomalacia

Malignancy
 For dyspneic patients, use Siemens Flash mode Siemens Flash mode: This high-pitch dual-source scanning technique reduces scan time and thus motion artifact, but cannot be used in larger patients due to limited field-of-view.
 to reduce respiratory motion artifact.

1. Venous phase of chest (40-60 seconds)
● Note: Since many oncology patients are on nephrotoxic medications, oncologists may request that studies be performed without IV contrast.

Pulmonary embolism
 Images are acquired during quiet breathing or with noninspiratory breath hold. Avoid deep inspiration, which transiently reduces pulmonary arterial enhancement by causing disproportionate influx of unenhanced blood from the IVC. Use Siemens Flash mode Siemens Flash mode: This high-pitch dual-source scanning technique reduces scan time and thus motion artifact, but cannot be used in larger patients due to limited field-of-view.
 to reduce respiratory motion artifact.

1. Pulmonary arterial phase of chest
● Acquisition is timed via contrast bolus tracking. An ROI drawn in the main pulmonary artery triggers acquisition when its internal enhancement reaches 150-200 HU.
 Pearls      
● Pulmonary embolism CT technique does not use gating.
● Noninspiratory imaging important to avoid transient attenuation artifact, due to contrast dilution from mixing of IVC blood if patient Valsalvas.
● Use high concentration ≥350 mgI/mL for larger patients (higher enhancement).
● A high iodine delivery rate is important for image quality (infusion rate at least 5 mL/second).
● Use high-pitch mode Siemens Flash mode: This high-pitch dual-source scanning technique reduces scan time and thus motion artifact, but cannot be used in larger patients due to limited field-of-view.
 to reduce respiratory motion artifact, if possible.
○  Requires use of both tubes
○  Smaller field of view
● Critical for PE imaging is < 1 mm reconstruction section.
Illustrative cases
 
Case 1: Pulmonary artery timing using bolus tracking technique on a 128-slice scanner in 59 year old male patient. With ROI tracker in the main pulmonary artery, a trigger of 217 HU results in excellent quality pulmonary arterial enhancement.
Case 2: Pulmonary embolism identified as cause of chest pain on coronary artery CT. The embolism is not well seen on 5 mm sections (A,B), but visualized very well on 0.75 mm axial section and coronal MPR (C,D).

(A) 5 mm slice thickness
(B) 5 mm slice thickness

(C) 0.75 mm slice thickness
(D) Coronal MPR
 

 
BROUGHT TO YOU BY:          MY-LINH NGUYEN, MD            KRISTIN PORTER, MD, PHD          PAMELA JOHNSON, MD
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