CT Pulmonary Angiography

1. Normal CTPA
Dr. Yash Kumar Achantani
OSR

2. What is CTPA
CT pulmonary angiography (CTPA) is a medical diagnostic test
that employs computed tomography to obtain an image of the
pulmonary arteries.
CTPA was introduced in the 1990s as an alternative to
ventilation/perfusion scanning, which relies on radionuclide
imaging of the blood vessels of the lung.
Because of its minimally invasive nature and high sensitivity and
specificity, CTPA has evolved into the first line imaging study for
the evaluation of suspected pulmonary embolism.

3. Images are acquired using a breath hold technique during the
pulmonary arterial enhancement phase following intravenous
contrast material injection, with pulmonary embolism
appearing as a filling defect in the otherwise densely opacified
pulmonary artery.

4. Pulmonary Artery Anatomy
The main pulmonary artery (MPA) is intrapericardial and courses
posteriorly and superiorly from the pulmonic valve. It divides
into the left pulmonary artery (LPA) and right pulmonary artery
(RPA) at the level of the fifth thoracic vertebra.
The RPA is longer than the LPA and crosses the mediastinum,
sloping slightly inferiorly to the right lung hilum. The LPA
represents the continuation of the MPA.
Segmental and subsegmental pulmonary arteries generally
parallel segmental and subsegmental bronchi and run alongside
them. This is in contrast to the course of most pulmonary veins,
which run independently of bronchi within interlobular septa.

5. The segmental arteries are named according to the
bronchopulmonary segments that they feed.
However, the proximal portions of the arteries to the posterior
subsegment of the left upper lobe and the lingular arteries can
run independently of their respective bronchi for short
segments.
Also, there are frequently accessory arteries from
neighbouring segments, particularly in the right upper lobe.
Segmental and subsegmental pulmonary arteries vary
considerably in the location of their origins, in whether they
arise as common trunks with other arteries or as separate
arteries, and in their number.

13. Indications
Pulmonary embolism
Aortic dissection
Aortic overloading
Left ventricular stress
Teratology of Fallot

14. Contraindications
Renal failure
Severe diabetes
Allergic to contrast reactions
Pregnant patients

15. PREPERATION
Enquire about pregnancy from females.
Renal parameters are to be checked.
Nil oral preparation for 4-6 hours
Informed consent is to be got from patient
All metal objects are to be removed from the region of interest
Patient is changed into hospital’s cotton apron.
Enquire about allergic history
A prominent vein in patients upper limb is catheterised with 18-
20 guage venflon.

16. CT Technique
Patient is positioned feet first with the help of laser localizers at
the level of sternal notch with coronal beam at mid-axillary line.
Proper immobilization should be done.
Proper breath hold instructions should be given.
Ensure the patient connected IV lines, are long enough to allow
full travel of the couch without being pulled or entangled while
undergoing a CT.

17. Test dose of about 2 – 5 ml of contrast is injected and patient is
observed for any reaction associated.
1.2ml /kg (body weight) of non-ionic iodinated contrast
medium is injected intravenously into the patient using a
pressure injector at a Rate of injection being 4-5 ml /sec, and
scan is performed with no delay.
For good timing bolus tracking is needed.A ROI is placed in the
pulmonary trunk.
When the treshhold of 150 HU is reached, the patient is asked
to breath in and scanning is started immediately.

18. Images of the thorax in a caudal–cranial direction. The caudal–
cranial direction is used because most emboli are located in
the lower lobes and, if the patient breathes during image
acquisition, there is more excursion of the lower lobes
compared with the upper lobes.
Contrast-enhanced helical CT of the veins of the lower
extremities is performed using the same contrast bolus as used
for chest CT.
Images of the iliac, femoral, and popliteal veins are obtained 3
minutes after the onset of the initial contrast injection.

20. CTPA

21. Right Side

22. Apical (A1)
Anterior (A3)

23. Lateral (A4)
Medial (A5)
Superior (apical) (A6)

24. Medial basal (paracardiac) (A7) , Anterior basal (A8)
Lateral basal (A9) , Posterior basal (A10)

25. Left side

26. Apicoposterior (A1+2)
Anterior (A3)

27. Superior lingular (A4)
Inferior lingular (A5)
Superior (apical) (A6)

28. Anteromedial (A7+8)
Lateral basal (A9)
Posterior basal (A10)

30. Artefacts

31. Transient interruption of contrast
TIC is a flow artefact, that consists of relatively poor contrast
enhancement in the pulmonary arteries, while there is good
enhancement in the SVC and also in the aorta.
This vascular phenomenon occurs when the patient performs a
deep inspiration just before the scan starts, resulting in
increased venous return of unopacified blood from the inferior
vena cava (IVC).
More unopacified blood from the IVC than opacified blood from
the SVC enters the right atrium resulting in poor enhancement of
the pulmonary arteries.

32. Transient Interruption of Contrast:
Deep inspiration results in dilution
of contrast in the right atrium by
unopacified blood from the inferior
vena cava

33. 1. Optimal
2. Too late.
3. Transient interruption of contrast

34. Motion Artifacts
Respiratory motion artifacts are the most common cause of an
indeterminate CTPA and can be a cause of misdiagnosis of
pulmonary embolism.
They are best seen on lung window settings that show
composite images of vessels. A rapid change in position of
vessels on contiguous images also confirms motion artifact.
At the moment, the breath-hold required for 16-MDCT is
approximately 10 seconds.
In dyspneic patients, oxygen supplementation can help the
patient provide the desired period of apnea.

35. Streak Artifacts
Streak artifact that obscures pulmonary vessels because of
metallic implants can make a study indeterminate.
Additional imaging with V/Q scintigraphy or pulmonary
angiography may be necessary.
Streak artifact from high-density contrast material in the
superior venacava can obscure adjacent pulmonary arteries.
The frequency of this artifact can be reduced by using a saline
bolus immediately after the contrast material injection.

36. ADVANTAGES
Less time consuming.
Non-invasive nature.
Almost all radiology departments have CT scan.
Less complication than conventional (elevated pulmonary artery
pressures).
Lesser volume of contrast needed.
Simple post procedure care.
Can be done in out patient basis.