WSO December 2023 – Issue 3 - 1229

Pham et al.
1229
using DECT is required for accurate NWU measurements post-thrombectomy. Future quantitative studies analyzing CT
after thrombectomy should consider occult contrast retention.
Keywords
Infarction, edema, net water uptake, thrombectomy, dual-energy CT
Received: 2 February 2023; accepted: 24 May 2023
Introduction
Follow-up computed tomography (CT) at 24-h post-treatment
is routinely used to guide clinical management and is
an established modality for assessing radiological outcomes
in stroke research. Residual iodine contrast retention
is a phenomenon specific to follow-up CT that is increasingly
seen in the modern era of thrombectomy for ischemic
stroke. Iodine extravasation is most commonly recognized
immediately after endovascular thrombectomy (EVT), and
may account for 27-84% of hyperdense lesions on CT at
24 h.1-4 As iodine contrast media is known to be incrementally
eliminated in a two-compartment model based on
early pharmacokinetic studies, the high prevalence of visible
contrast staining suggests smaller amounts of iodine
contrast that may not be qualitatively detectible by visual
inspection may also be present in tissue (i.e. occult contrast
retention), on early follow-up imaging at 24 h.5
Visible contrast extravasation mimics hyperdense blood
products and complicates accurate identification of hemorrhagic
transformation, with implications for prognostication
and clinical decisions regarding post-stroke
antithrombotic use. Similarly, occult contrast retention may
confound interpretation of Hounsfield unit (HU)-based
metrics on follow-up CT imaging, such as net water uptake
(NWU), an increasingly applied measure of cerebral edema
that relies on the degree of hypodensity of the infarct.6
NWU measured on pre-treatment baseline imaging has
been shown to be potentially useful for estimating lesion
age and guiding reperfusion treatment in patients with
unknown time of onset and large core.7,8 However, NWU
has also been increasingly applied to post-treatment followup
imaging to study the treatment effect of EVT on infarct
evolution and cerebral edema, without consideration for the
potential effect of occult angiographic retention.9-14
Dual-energy CT (DECT) is a commonly available CT
technique that can distinguish between iodine contrast
extravasation and blood products.1,4,15-18 Using two X-ray
spectra to characterize varying attenuation properties when
exposed to different photon energy, DECT can identify and
quantify iodine, and subsequently reconstruct an iodineadjusted
image representing a non-contrast CT (NCCT)
brain with iodine components subtracted (virtual non-contrast
(VNC)). In acute stroke, DECT has been most widely
applied to differentiate post-EVT hemorrhagic transformation
and contrast extravasation when there is frank
hyperattenuation.1-4 DECT has also been used in liver and
renal tract imaging to determine whether subtle increased
attenuation in soft tissue observed after a contrast-enhanced
scan is due to contrast retention in the parenchyma, or a true
reflection of tissue properties.15 We extended this application
to study whether contrast is retained in the brain parenchyma
after iodine contrast exposure even when there is
minimal visually observed hyperattenuation.
Aims
This study aimed to assess (1) the presence of retained contrast
on 24-h CT post-thrombectomy, (2) factors associated
with amount of contrast retained, and (3) its impact on the
accuracy of NWU measurements.
Methods
Study design and inclusion criteria
Patients presenting between November 2021 and May
2022, to two Comprehensive Stroke Centers, who underwent
thrombectomy for acute anterior circulation large vessel
occlusion in a prospectively maintained institutional
thrombectomy registry database were retrospectively studied.
At both centers, follow-up CT imaging was performed
at 24-h post-treatment with concurrent conventional single
spectra CT (Siemens Healthineers, 120 kV) and dual-source
DECT (two scanners were used at Center 1: Siemens
SOMATOM Definition Flash, Siemens Healthineers,
Germany, tube A 100 kb/280mAs, tube B Sn140/280mAs;
and Siemens SOMATOM Definition Force, Siemens
Healthineers, Germany, tube A 100 kV/280 mAs, tube B
Sn150/175 mAs, continuous image acquisition with construction
slice at 5 mm width and 5 mm interval, matrix
512 × 512; Center 2: Siemens SOMATOM Force, Siemens
Healthineers, Germany, tube A 100 kb/312 mAs, tube B
Sn150/250 mAs, continuous image acquisition with construction
slice at 5 mm width and 2.5 mm interval, matrix
512 × 512) as standard of care. Patients were excluded if
they had: (1) posterior circulation stroke, (2) medical treatment
without thrombectomy, (3) hyperdensities within the
infarct from hemorrhagic transformation or overt contrast
extravasation, visually and qualitatively assessed by an
experienced neurologist blinded to clinical data on imaging
at 24 h, (4) pre-existing cerebral hemispheric structural
International Journal of Stroke, 18(10)
WSO December 2023 – Issue 3

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