# Virtual monochromatic versus conventional polychromatic CT images in patients with acute bowel ischaemia

## TL;DR

Virtual monochromatic CT images are as effective as traditional CT for detecting acute bowel ischaemia, allowing for reduced radiation dose.

## Contribution

Demonstrates that virtual monochromatic CT images can replace traditional non-enhanced scans for diagnosing acute bowel ischaemia.

## Key findings

- Virtual monochromatic and conventional CT images showed similar diagnostic accuracy for detecting acute bowel ischaemia.
- Significant differences in bowel wall density were observed between healthy and pathological segments using virtual monochromatic images.
- Using virtual non-enhanced images can reduce radiation exposure without compromising diagnostic quality.

## Abstract

To compare 40 keV virtual monochromatic images (VMIs) with conventionally acquired polychromatic multi-detector CT images (CONV) in patients with acute bowel ischaemia (ABI).

We retrospectively included 48 consecutive patients (38 males, mean age 69 years) with pathologically proven ABI over 40 months. They underwent portovenous dual-energy multi-detector CT followed by surgery within < 48 h. Nineteen patients had VMIs, and 29 had CONV after non-enhanced acquisition. After dividing the small and large bowel into 10 segments, two radiologists blinded to the exact localisation of the ABI read the VMIs and CONV images separately. After this qualitative analysis, bowel wall density was assessed quantitatively on (virtual) non-enhanced and portovenous images.

Qualitative analysis showed good overall sensitivity (75.9–82%) and specificity (85.9–88.7%) for localising ABI on VMIs and CONV images without significant differences. Inter-observer agreement was important or near perfect (kappa 0.61–0.83). Quantitative analysis revealed significant differences in wall density between healthy and pathological bowel segments for nearly all VMIs and CONV images, not only when analysing the (virtual) non-enhanced and portovenous phases separately, but also when subtracting wall density (portovenous minus (virtual) non-enhanced phase). Wall density delta (healthy minus pathological wall) showed no significant differences between VMIs and CONV images.

VMIs and CONV images had good diagnostic value and important inter-reader agreement for localising ABI using (virtual) non-enhanced and portovenous phases, without significant qualitative or quantitative differences. Therefore, we can rely on the virtual non-enhanced phase instead of additionally acquiring a non-enhanced phase, enabling considerable dose reduction.

Question
Can we rely on virtual monochromatic CT images to detect reduced or absent bowel wall enhancement in acute bowel ischaemia?

Findings
Virtual monochromatic CT images have equal diagnostic value for detecting acute bowel ischaemia as conventionally acquired polychromatic CT images without significant qualitative or quantitative differences.

Clinical relevance
Significant differences in bowel wall density between healthy and pathological segments on subtraction virtual monochromatic images allow us to rely on the virtual non-enhanced phase instead of acquiring an additional non-enhanced phase in acute bowel ischaemia, leading to dose reduction.