BODY CT PROTOCOL DESIGN


 
 Oral contrast: In general, give 1000 mL PO water for the protocols below.
Aorta:
Acute aortic syndrome
 If ascending aortic pathology is suspected, use ECG gating (preferably in combination with
high-pitch mode) Siemens FLASH mode: This high-pitch dual-source scanning technique reduces both radiation dose and scan time.
 
Adding ECG gating to any study (whether prospective or retrospective gating) increases overall radiation dose. Using high-pitch mode can minimize the added radiation.
 
Although high-pitch mode's faster scan time reduces motion artifact, this alone is not sufficient to eliminate motion at the aortic root in many cases. Therefore, a combination of ECG gating and high-pitch mode (FLASH gating) is the best approach.
 
The only exception to use of FLASH gating is in very large patients, where high-pitch mode results in noisier images. In these cases, gating with standard pitch may be preferred. to eliminate cardiac pulsation artifact.

1. (Optional) ± Noncontrast images to evaluate for intramural hematoma. Alternatives:
● Use arterial images to evaluate for intramural hematoma. Look for wall thickening >5 mm and wall hyperattenuation >45 HU.
● Generate virtual noncontrast images using dual-energy CT.
2. Early arterial phase of entire aortic vasculature
 Pitfall      
● Cardiac pulsation artifact can mimic dissection in the ascending aorta
○  Scan correctly the first time to avoid this pitfall. Use ECG gating to eliminate cardiac pulsation artifact.
○  Use of high pitch in thinner patients enables prospective gating at a lower radiation dose to the patient.

Ungated
Gated

Ungated
Gated
 
First case from: Johnson PT, Horton KM, Fishman EK. Volume visualization of the ascending thoracic aorta using isotropic MDCT data: protocol optimization. AJR Am J Roentgenol. 2010 Nov;195(5):1082-7.
 Pearl      
● MPRs must be used to investigate the aortic root.
Illustrative case: 31 year old man with acute hemopericardium. Noncontrast coronal (A) and axial (B) CT shows high attenuation pericardial fluid (H) and an ascending aortic intramural hematoma (arrow in B). After IV contrast administration, an aortic root pseudoaneurysm (arrowheads) is difficult to appreciate on axial sections (C) but visualized with high confidence on coronal MPR (D).

(A) Noncontrast coronal
(B) Noncontrast axial

(C) Contrast-enhanced axial
(D) Contrast-enhanced coronal

Aorta:
Aortic stent/graft
 1. Noncontrast images of stent/graft only
● Distinguishes calcification/surgical material from endoleak.
● Dual energy CT could also be used to create virtual noncontrast images.
2. Early arterial phase of entire aortic vasculature
3. Delayed phase (60 seconds after arterial acquisition) of stent only
● Some endoleaks more conspicuous on delayed/venous phase
Illustrative case: Patient status post descending thoracic endovascular stent repair. Axial precontrast (A,C) and arterial phase (B,D) images illustrate the importance of pre- and post-contrast acquisitions in distinguishing an endoleak (arrow in B) from calcification in the aortic sac (circles in C and D).

(A) Precontrast
(B) Arterial phase

(C) Precontrast
(D) Arterial phase
Aorta:
Preoperative aorta
 1. Early arterial phase of entire aortic vasculature
● If aortic root pathology is suspected, eliminate cardiac pulsation artifact using ECG gating, preferably in combination with high-pitch mode. Siemens FLASH mode: This high-pitch dual-source scanning technique reduces both radiation dose and scan time.
 
Adding ECG gating to any study (whether prospective or retrospective gating) increases overall radiation dose. Using high-pitch mode can minimize the added radiation.
 
Although high-pitch mode's faster scan time reduces motion artifact, this alone is not sufficient to eliminate motion at the aortic root in many cases. Therefore, a combination of ECG gating and high-pitch mode (FLASH gating) is the best approach.
 
The only exception to use of FLASH gating is in very large patients, where high-pitch mode results in noisier images. In these cases, gating with standard pitch may be preferred.
● Make measurements on axis-adjusted images, not the default axial images.
IVC thrombosis
 1. Late venous phase (90 or 120 seconds) of abdomen and pelvis
 
 
BROUGHT TO YOU BY:          MY-LINH NGUYEN, MD            KRISTIN PORTER, MD, PHD          PAMELA JOHNSON, MD
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