PICTORIAL ESSAY
Multi-energy spectral CT: adding value in emergency body imaging
Gopal V. Punjabi
1
Received: 1 November 2017 / Accepted: 20 November 2017 / Published online: 28 November 2017
#
American Society of Emergency Radiology 2017
Abstract
Most vendors offer scanners capable of dual- or multi-energy computed tomography (CT) imaging. Advantages of multi-energy
CT scanning include superior tissue characterization, detection of subtle iodine uptake differences, and opportunities to reduce
contrast dose. However, utilization of this technology in the emergency department (ED) remains low. The purpose of this
pictorial essay is to illustrate the value of multi-energy CT scanning in emergency body imaging.
Keywords Spectral
.
Computed tomography
Introduction
Dr. Godfrey Hounsfield introduced the concept of multi-
energy CT in his seminal paper published in 1973, and
described the ability of the CT scanner to Bdetermine ap-
proximately the atomic number of material within the slice
by taking two pictures, at 100 and 140 kV^ [1]. Most ven-
dors now offer scanners capable of multi-energy imaging,
and options available include dual-source CT, rapid kVp
switching, and sequential CT scanners [2]. At the author’s
institute, the chosen vendor offers multi-energy CT scan-
ning with a novel dual-layer detector (Philips IQon spectral
CT).
Conventional CT utilizes a polychromatic beam, but
the energy levels are not separated in image generation.
In a dual-layer detector, the thinner top layer (closer to the
patient) measures the low-energy photons, and the thicker
bottom layer measures the high-energy photons. Complex
material decomposition algorithms [3] (beyond scope of
this review) are then utilized to generate multiple image
sets, including virtual non-contrast (VNC), iodine maps,
and effective atomic number; as well as virtual monochro-
matic image sets. Spectral regions of interest (ROI) can be
used to obtain further information about specific tissues or
lesions.
The purpose of this pictorial essay is to illustrate the
value of multi-energy CT in emergency body imaging,
including (1) characterization of incidental lesions, (2)
iodine detection and subtraction, (3) assessment of tissue
perfusion, (4) contrast dose reduction, and (5) tissue
characterization.
Characterization of incidental lesions
Incidental lesions are very common in body imaging and re-
sult in substantial cost to the health care system in terms of
follow-up imaging [4]. There is also a personal cost to the
patient in terms of increased anxiety.
In the ED, most abdominal CT scans are obtained with
IV contrast. In a dual-layer system, spectral imaging is
Balways on,^ and spectral images (including VNC im-
ages) can be reconstructed retrospectively. Attenuation
value of lesions on VNC images has been shown to cor-
relate very well with true non-contrast scans [5].
Therefore, adrenal lesions can be characterized as benign
adenomas if the attenuation value on VNC is less than
10 HU (Fig. 1)[6].
Renal lesions can often be characterized as benign cysts if
the attenuation is that of simple fluid (less than 20 HU) [7].
Renal cysts can be higher density because of hemorrhagic
content and require follow-up imaging with multiphase
contrast-enhanced CT or MRI to evaluate for enhancement
[8]. By showing uptake of contrast, iodine maps can readily
differentiate between benign hyper-attenuating cyst and an
enhancing mass (Figs. 2 and 3).
* Gopal V. Punjabi
Gopal.Punjabi@hcmed.org
1
Hennepin County Medical Center, 701, Park Ave,
Minneapolis, MN 55455, USA
Emergency Radiology (2018) 25:197–204
https://doi.org/10.1007/s10140-017-1569-4
@Phil_Robichaud
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