2015 ISAKOS Biennial Congress ePoster #2012

Quantifiable Imaging Biomarkers for Evaluation of the PCL Using 3T MRI: A Feasibility Study

Charles P Ho, MD, PhD, Vail, CO UNITED STATES
Katharine J. Wilson, MSc, Vail, CO UNITED STATES
Brian M. Devitt, MD, FRCS, FRACS, Melbourne, VIC AUSTRALIA
Rachel K. Surowiec, MSc, Vail, CO UNITED STATES
Jurgen Fripp, PhD, Brisbane, Queensland AUSTRALIA
W. Sean Smith, PhD, Vail, Colorado UNITED STATES
Ulrich Josef Spiegl, MD, Leipzig GERMANY
Grant J. Dornan, MS, Vail, CO UNITED STATES
Robert F. LaPrade, MD, PhD, Edina, MN UNITED STATES

Steadman Philippon Research Institute, Vail, Colorado, USA

FDA Status Cleared

Summary: T2 and T2* mapping was performed on an asymptomatic PCL population using 3T MRI. The distal third of the PCL had significantly higher T2 values, which may be relevant to injuries commonly found in the mid or proximal thirds. The results provide a normative baseline of T2 and T2* values for the asymptomatic PCL for comparison with chronic PCL injuries.

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Abstract:

Introduction

While conventional magnetic resonance imaging (MRI) is an accurate tool for detecting acute posterior cruciate ligament (PCL) injuries, it is less reliable in the diagnosis of chronic injuries where the ligament may appear to be healed. Quantifiable measures of ligament scarring and degeneration would be useful in the clinical diagnosis of these injuries. The objective of this study was to quantify the T2 and T2* mapping properties, including texture variables (entropy, contrast, variance, homogeneity), in clinically relevant subregions of the asymptomatic PCL. It was hypothesized that the T2 and T2* values would be consistent throughout the ligament.

Methods

This study was IRB approved. Twenty-five asymptomatic subjects were prospectively enrolled (mean age: 40.6±13.0, 11m/14f). Subjects were deemed asymptomatic through an objective clinical examination, subjective score, and morphologic MR evaluation. Unilateral knee scans were acquired with a 3.0T MRI system using a 15-channel multi-element phased-array knee coil. The MRI protocol included multi-echo spin-echo T2 mapping and T2* mapping sequences in the sagittal plane through the notch and PCL. Manual segmentations were performed and custom software was used to calculate T2 and T2* values. The PCL was divided into three regions of interest by creating a 3D centerline along the ligament and dividing it into thirds (proximal, mid, distal). Average T2 and T2* values, as well as texture variables (entropy, contrast, variance, homogeneity), were calculated for each third. Intra- and inter-rater reliability was assessed across three raters and two time points.

Results

The mean T2 values in each subregion were 36.7ms, 29.2ms and 29.6ms for the distal, middle and proximal regions, respectively. The distal third of the PCL had significantly higher variance and contrast, and significantly lower entropy than the other two regions. Intra- and inter-rater reliability was good to excellent (ICC: 0.7-0.8). For T2* mapping, the mean T2* values demonstrated positive skew and were therefore presented using the median. The median T2* values were consistently 7.3ms in all regions of the asymptomatic PCL.

Discussion

Contrary to our hypothesis, the T2 values of the asymptomatic PCL were not consistence throughout the ligament, with the distal third demonstrating higher T2 values, as well as higher variance and contrast and lower entropy. This may be relevant to injuries commonly found in the mid or proximal thirds. Good to excellent intra- and inter-rater reliability suggests a robust methodology. A limitation of this study was the disparity in genders within the age groups, in particular having younger males and older females.

Significance

The results of this study contribute toward

Methodology

and normative baseline of T2 and T2* values for the asymptomatic PCL population, and can be used for comparison with chronic PCL injuries.