# Time-resolved 3D imaging opportunities with XMPI at ForMAX

## TL;DR

This paper introduces XMPI, an innovative X-ray imaging technique that captures multiple projections simultaneously without sample rotation, enabling high-speed 3D imaging of dynamic samples at the ForMAX beamline.

## Contribution

The paper presents the implementation of XMPI at ForMAX, demonstrating its ability to perform time-resolved 3D imaging without rotation, overcoming limitations of traditional tomography methods.

## Key findings

- Achieved at least 12.5 kHz frame rates with 4 μm pixels for fibers.
- Demonstrated 40 Hz acquisitions with 1.3 μm pixels for multi-phase flow.
- Set the foundation for a permanent XMPI endstation at ForMAX.

## Abstract

X-rays are commonly used in imaging experiments due to their penetration power, which enables non-destructive resolution of internal structures in samples that are opaque to visible light. Time-resolved X-ray tomography is the state-of-the-art method for obtaining volumetric 4D (3D + time) information by rotating the sample and acquiring projections from different angular viewpoints over time. This method enables studies to address a plethora of research questions across various scientific disciplines. However, it faces several limitations, such as incompatibility with single-shot experiments, challenges in rotating complex sample environments that restrict the achievable rotation speed or range, and the introduction of centrifugal forces that can affect the sample's dynamics. These limitations can hinder and even preclude the study of certain dynamics. Here, we present an implementation of an alternative approach, X-ray Multi-Projection Imaging (XMPI), which eliminates the need for sample rotation. Instead, the direct incident X-ray beam is split into beamlets using beam splitting X-ray optics. These beamlets intersect at the sample position from different angular viewpoints, allowing multiple projections to be acquired simultaneously. We commissioned this setup at the ForMAX beamline at MAX IV. We present projections acquired from two different sample systems - fibers under mechanical load and particle suspension in multi-phase flow - with distinct spatial and temporal resolution requirements. We demonstrate the capabilities of the ForMAX XMPI setup using the detector's full dynamical range for the relevant sample-driven spatiotemporal resolutions: i) at least 12.5 kHz framerates with 4 micrometer pixel sizes (fibers) and ii) 40 Hz acquisitions with 1.3 micrometer pixel sizes (multi-phase flows), setting the basis for a permanent XMPI endstation at ForMAX.