# Ultrashort Echo Time Double Echo Steady-State MRI for Quantitative Conductivity Mapping in the Knee: A Feasibility Study

## TL;DR

This study introduces a new MRI technique to map tissue conductivity in the knee, which could help diagnose and monitor joint diseases like osteoarthritis.

## Contribution

A novel ultrashort echo time MRI method for quantitative conductivity mapping in musculoskeletal tissues is developed and validated.

## Key findings

- UTE-QCM successfully visualized distinct conductivity values in a phantom and healthy volunteers.
- The integral-based QCM method showed improved noise robustness compared to parabolic fitting.
- UTE-QCM maps captured both long and short T2 tissues in the knee.

## Abstract

Tissue conductivity reflects the amount and movement of ions, such as sodium (most abundant in the human body), which are important for tissue health. Measuring conductivity can provide valuable information about joint and musculoskeletal disorders. In this study, we developed a novel imaging method using ultrashort echo time MRI to achieve conductivity mapping in the knee. This approach successfully visualized distinct conductivity values in a phantom and healthy volunteers. The technique could help doctors better detect and monitor joint diseases, like osteoarthritis, and may guide future research into new diagnostic tools for musculoskeletal conditions.

Background/Objectives: Tissue conductivity reflects ionic composition (e.g., sodium), providing critical insights into various diseases. Ultrashort echo time quantitative conductivity mapping (UTE-QCM) offers a method to obtain this information, which is particularly effective for musculoskeletal (MSK) tissues with short T2 relaxation times. The aim of this study is to develop a UTE-QCM framework using ultrashort echo time double echo steady-state (UTE-DESS) and validate its feasibility in the knee. Methods: An ultrashort echo time double echo steady-state (UTE-DESS) sequence was used to acquire S+ and S− images and estimate the transmit radiofrequency field (B1+) phase at 3T. The B1+ phase was derived by canceling the phase evolution in the free induction decay using these images. This phase data was then processed using two widely used QCM reconstruction methods for comparison: parabolic fitting and an integral-based method. The proposed UTE-QCM framework was validated using a phantom containing three different concentrations of sodium chloride (0%, 0.5%, and 1%). Additionally, three healthy volunteers were recruited to validate UTE-QCM in knee imaging. Results: In both phantom and in vivo experiments, the integral-based QCM demonstrated improved robustness to noise compared to parabolic fitting. In the sodium phantom, the estimated conductivity showed high linearity with sodium concentrations. In the in vivo knee, the generated conductivity maps successfully visualized both long and short T2 tissues. Conclusions: We demonstrated the feasibility of UTE-QCM as a novel quantitative imaging tool targeting short T2 tissues in the MSK system. This technique may facilitate the diagnosis and prognosis of joint disorders.