Non-invasive method to estimate Pulmonary Vascular resistance on CT
Pulmonary angiography
• Kaushik Shahir MD • Kevin Fuhrman• Zachary Laste MD• Scott Baginski MD• Kenneth Presberg MD• Sushil Sonavane MD• Lawrence Goodman MD• Dhiraj Baruah MD
No relevant disclosures
Pulmonary vascular resistance - PVR
Specific parameter measured on pulmonary catheter angiography
Normal value3 wood units
240 dynes/cm
PVR – key role in assessment and management of pulmonary hypertension
Pulmonary arterial intimal hyperplasia
Pulmonary arterial medial thickening
Increased vascular tone
PVR
Treatment is directed to reduce PVR
Pathophysiology
Test bolus - CTPA
Technique where-by the passage of an intravenous contrast bolus can be tracked through the pulmonary vascular system
Commonly used to plan the timing for
injection and image acquisition for CTPA
As the contrast bolus traverses through the pulmonary circulation , the attenuation curve shows a sigmoidal shape comprised of a rise in the attenuation with a subsequent drop in the signal intensity with time
The immediate factor which decide how shallow or steep the rise and fall of this curve is predominantly decided by the pulmonary vascular resistance
Normal test bolus curve
Test bolus in a normal patient
Factors affecting the shape of bolus curve
• Pulmonary vascular resistance
• Right ventricular function• Pulmonic valve function• Patency of injected
systemic vein
Parameters used to assess the test bolus
Pulmonary transit time PTT
Att
enua
tion
HU
Time (seconds)
PTT
Time required for contrast to travel from PA to left atrium
Parameters used to assess the test bolus
Time to peakTTP
Att
enua
tion
HU
Time (seconds)
TTP
Time required for contrast to reach peak attenuation in the PA
Parameters used to assess the test bolus
Full width at half maximumFWHM
Att
enua
tion
HU
Time (seconds)
FWHMWidth of the attenuation curve at half the maximum attenuation value
0 2 4
6 8 10
12 1614
A patient with PVR of 2.5 wood units
What’s normal FWHM?
Time (seconds)
Attenuation (HU)
0 102 604 1406 2508 320
10 18012 12014 9016 50
0
50
100
150
200
250
300
350
0 2 4 6 8 10 12 14 16 18
TTP = 8 seconds
FWHM = 6 seconds
The green shaded portion of the attenuation values chart demonstrates the FWHM for the test bolus shown on the previous slide
The same patient with PVR of 2.5 wood units
Abnormal FWHM
Test bolus for CTPA in a patient with severe PH (type 1) with PVR of 20 wood units
0 2 4 6
8 10 12 14
16 18 20 22
24 26 28 30
Each image in the test bolus of the same patient with severe PH with PVR of 20 wood units
Time Attenuation (HU)0 402 504 586 658 90
10 11012 14014 16016 18518 17020 15922 13424 11026 8528 5530 48
The green shaded portion of the attenuation values chart demonstrates the FWHM for the test bolus shown on the previous slide
TTP – 16 sFWHM – 18s
The same patient with severe PH with PVR of 20 wood units
Causes ?
The main cause of increased FWHM is logically a pathophysiological process
which leads to prolonged slow circulation
This is an indirect representation of pulmonary vascular resistance
(PVR)
Our experience and research
Normal FWHM < 8 seconds
When FWHM > 12 seconds, the likelihood of high PVR is extremely high!
ParameterCorrelation coefficient (R) [p-value]
mPAP PVR PVRi
MPA 0.34 [0.12] 0.19 [0.42] 0.12 [0.59]
LPA 0.10 [0.65] 0.13 [0.56] 0.22 [0.34]
RPA 0.19 [0.4] 0.09 [0.69] 0.13 [0.56]
MPA/Ao 0.46 [0.03] 0.47 [0.03] 0.44 [0.04]
A/B 0.37 [0.09] 0.47 [0.03] 0.01 [0.9]
R/L 0.02 [0.93] 0.24 [0.3] 0.21 [0.3]
TTP 0.62 [002] 0.75 [0.0001] 0.65 [0.001]
FWHM 0.68 [0.0004] 0.84 [0.00001] 0.83 [0.00001]
MPA – Main pulmonary artery diameter, LPA – left PA diameter, RPA – right PA diameter, MPA/Ao – Main PA/Aorta ratio, A/B – Arterio-bronchial ratio, R/L – Right/Left vetricular ratiomPAP – Mean PA pressure, PVRI – pulmonary vascular resistance index
Results from institutional study showed a very strong correlation for TTP and FWHM with mPAP, PVR and PVRI as compared to other conventional parameters
R = 0.64947
R = 0.745665R = 0.617647
There is moderate positive correlation between TTP and PVR, PVRI and mPAP
Data from our institutional study comprised of 22 adult patients with pulmonary hypertension
R = 0.83
R = 0.835274R = 0.684466
There is strong positive correlation between FWHM and PVR, PVRI and mPAP
How to put this knowledge into daily usage?
Test bolus is a routinely performed step prior to CT pulmonary angiography to plan the timing of
the injection.
The curve can be carefully evaluated to calculate FWHM
Each CT image is acquired at 2 seconds
False positive – Increased FWHM, TTP
Right ventricular dysfunction
Pulmonic valve regurgitation
Hemo-dilution
Severe bradycardia
False negative – Normal FWHM,TTP
Valsalva maneuver – clarify – split bolus
Large AVM
Severe tachycardia
Limitation
Test bolus may not be available or routinely performed as many groups use bolus tracking
Some newer scanners have test bolus acquisition timing set at 1 second – which will require according changes in the calculations
Can have a suboptimal quality due to respiratory artefact
The scan acquisition may be prematurely terminated or started late by the CT technologist leading to inadequate information
Time (s) ROI0 312 324 336 638 137
10 18412 18614 15416 12018 9020 50
TTP 12FWHM 10
Catheter angiography :• mPAP – 45 mmHg• PVR - 7.4 Wood units• PVRI - 4.3
0
20
40
60
80
100
120
140
160
180
200
0 5 10 15 20 25
Case example 1 – 32 years old female with mild PH, type I
FWHM was mildly abnormal in patient with PH and elevated PVR
Case example 2 Patient with moderate PH (type I)
Time Attenuation (HU)0 402 544 786 888 120
10 16012 13414 11216 8418 68
TTP – 10 sFWHM – 12s
PVR – 9 wood unitsGood correlation between FWHM and PVR
Case example 3 – 54 years old female with severe pulmonary hypertension
Time Attenuation (HU)0 842 1204 1386 2208 248
10 19012 16414 14416 11818 10420 8422 68TTP – 8 s
FWHM – 14s
PVR – 15 wood units
Case example 4- A 52 years old female with sarcoidosis
and marked PHTime Attenuation (HU)
0 442 524 646 878 108
10 13412 16914 19016 14518 10320 8922 6724 55
TTP – 14 sFWHM – 14s
PVR – 17 wood units
Conclusion
CTPA test bolus offers an excellent opportunity to confidently predict the status of pulmonary vascular resistance
Of the different parameters, FWHM has a strongest correlation with PVR
• FWHM < 8 seconds suggests normal PVR• FWHM> 12 seconds is highly suggestive of abnormal PVR
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Authors:Dr Kaushik Shahir – [email protected] Dhiraj Baruah – [email protected]
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