(2023) Turrion Gomollon | VNI PCCT may replace true noncontrast after EVAR

Daniel Stromer

In 110 patients undergoing EVAR surveillance, including 41 endoleaks, the authors compared conventional triphasic PCCT (true noncontrast + arterial + venous) with a biphasic strategy in which virtual noniodine (VNI) images reconstructed from the venous phase replaced the true noncontrast acquisition.

Endoleak detection was essentially preserved with VNI. Sensitivity was identical for each reader (0.95 vs 0.95 and 0.88 vs 0.88), while specificity remained similar; interreader agreement was substantial with both TNC (α = 0.716) and VNI (α = 0.756). Subjective image quality and noise were also comparable.

Replacing TNC with VNI could have reduced radiation exposure by approximately 38%. A caveat is imperfect calcium preservation: small aneurysm calcifications were erroneously removed in 15/110 patients (14%), although this affected endoleak diagnosis in only one case, producing a false-positive interpretation.

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Figure 2. Axial CT images at the level of the aortic aneurysm acquired with photon-counting detector CT in a 60-year-old man referred for follow-up imaging after EVAR: (A) true noncontrast images, (B) arterial phase, (C) venous phase with an arrow pointing at the endoleak, and (D) virtual noniodine images reconstructed from venous phase images.

Protocol

Detail	Value
Scanner	NAEOTOM Alpha
Software	VA50
Scan area	Thoracoabdominal aorta / EVAR surveillance
Scan mode	QuantumPlus multienergy
Acquisition phases	True noncontrast, arterial, venous
Tube voltage [kV]	120
IQ level	68
Dose modulation	CARE Dose4D
CTDIvol [mGy]	TNC 5.1 ± 1.5; arterial 3.74 ± 1.4; venous 4.65 ± 1.4
DLP [mGy·cm]	TNC 353.3 ± 108.1; arterial 258.9 ± 88.8; venous 320 ± 100
Total dose	CTDIvol 13.5 ± 3.9 mGy; DLP 932.2 ± 286 mGy·cm
Rotation time [s]	0.25
Pitch	1.2
Detector slice collimation	144 × 0.4 mm
Reconstruction slice thickness / increment [mm]	2.0 / 1.6
Iterative reconstruction	QIR 4
TNC reconstruction	70-keV VMI, Br36
VNI reconstruction	70 keV, PureCalcium, Qr36; reconstructed from venous phase
Arterial reconstruction	55-keV VMI
Venous reconstruction	60-keV VMI
Contrast	Iopromide, Ultravist 370 mg I/mL
Contrast volume	70 mL total
Contrast protocol	40-mL contrast bolus → 60-mL 1:1 contrast/saline mixture → 20-mL saline chaser
Injection rate	4 mL/s
Bolus triggering	Ascending aorta; 140 HU at 90 kV
Arterial phase	12 s after trigger threshold
Venous phase	70 s after trigger threshold

Key Results

Parameter	Main finding
Study population	110 patients; 41 endoleaks (37%)
Reader 1 sensitivity / specificity	TNC 0.95 / 0.84 vs VNI 0.95 / 0.86
Reader 2 sensitivity / specificity	TNC 0.88 / 0.98 vs VNI 0.88 / 0.94
Interreader agreement	TNC α = 0.716; VNI α = 0.756
Subjective image quality / noise	Both 4 [IQR 4–5]; no significant difference
Potential dose reduction	38% by eliminating the TNC acquisition

Source:
Turrion Gomollon AM, Mergen V, Sartoretti T, Polacin M, Nakhostin D, Puippe G, Alkadhi H, Euler A. Photon-Counting Detector CT Angiography for Endoleak Detection After Endovascular Aortic Repair: Triphasic CT With True Noncontrast Versus Biphasic CT With Virtual Noniodine Imaging. Investigative Radiology. 2023;58(11):816–821. doi:10.1097/RLI.0000000000000993.