Multiparametric MRI and Computational Modelling in the Assessment of Human Articular Cartilage Properties: A Comprehensive Approach

Abstract

Quantitative magnetic resonance imaging (qMRI) is a promising approach to detect early cartilage degeneration. However, there is no consensus on which cartilage component contributes to the tissue’s qMRI signal properties. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mi>T</mml:mi><mml:mn fontstyle="italic">1</mml:mn></mml:math>, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mi>T</mml:mi><mml:mn fontstyle="italic">1</mml:mn><mml:mi>ρ</mml:mi></mml:math>, and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:mi>T</mml:mi><mml:msup><mml:mrow><mml:mn fontstyle="italic">2</mml:mn></mml:mrow><mml:mrow><mml:mo>⁎</mml:mo></mml:mrow></mml:msup></mml:math> maps of cartilage samples (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M4"><mml:mi>n</mml:mi><mml:mo>=</mml:mo><mml:mn fontstyle="italic">8</mml:mn></mml:math>) were generated on a clinical 3.0-T MRI system. All samples underwent histological assessment to ensure structural integrity. For cross-referencing, a discretized numerical model capturing distinct compositional and structural tissue properties, that is, fluid fraction (FF), proteoglycan (PG) and collagen (CO) content and collagen fiber orientation (CFO), was implemented. In a pixel-wise and region-specific manner (central versus peripheral region), qMRI parameter values and modelled tissue parameters were correlated and quantified in terms of Spearman’s correlation coefficient <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M5"><mml:mi>ρ</mml:mi><mml:mi>s</mml:mi></mml:math>. Significant correlations were found between modelled compositional parameters and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M6"><mml:mi>T</mml:mi><mml:mn fontstyle="italic">1</mml:mn></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M7"><mml:mi>T</mml:mi><mml:msup><mml:mrow><mml:mn fontstyle="italic">2</mml:mn></mml:mrow><mml:mrow><mml:mo>⁎</mml:mo></mml:mrow></mml:msup></mml:math>, in particular in the central region (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M8"><mml:mi>T</mml:mi><mml:mn fontstyle="italic">1</mml:mn></mml:math>: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M9"><mml:mi>ρ</mml:mi><mml:mi>s</mml:mi><mml:mo>≥</mml:mo><mml:mn fontstyle="italic">0.7</mml:mn></mml:math> [FF, CFO], <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M10"><mml:mi>ρ</mml:mi><mml:mi>s</mml:mi><mml:mo>≤</mml:mo><mml:mo>-</mml:mo><mml:mn fontstyle="italic">0.8</mml:mn></mml:math> [CO, PG]; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M11"><mml:mi>T</mml:mi><mml:msup><mml:mrow><mml:mn fontstyle="italic">2</mml:mn></mml:mrow><mml:mrow><mml:mo>⁎</mml:mo></mml:mrow></mml:msup></mml:math>: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M12"><mml:mi>ρ</mml:mi><mml:mi>s</mml:mi><mml:mo>≥</mml:mo><mml:mn fontstyle="italic">0.67</mml:mn></mml:math> [FF, CFO], <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M13"><mml:mi>ρ</mml:mi><mml:mi>s</mml:mi><mml:mo>≤</mml:mo><mml:mo>-</mml:mo><mml:mn fontstyle="italic">0.71</mml:mn></mml:math> [CO, PG]). For <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M14"><mml:mi>T</mml:mi><mml:mn fontstyle="italic">1</mml:mn><mml:mi>ρ</mml:mi></mml:math>, correlations were considerably weaker and fewer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M15"><mml:mo stretchy="false">(</mml:mo><mml:mn fontstyle="italic">0.16</mml:mn><mml:mo>≤</mml:mo><mml:mi>ρ</mml:mi><mml:mi>s</mml:mi><mml:mo>≤</mml:mo><mml:mo>-</mml:mo><mml:mn fontstyle="italic">0.15</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math>. QMRI parameters are characterized in their biophysical properties and their sensitivity and specificity profiles in a basic scientific context. Although none of these is specific towards any particular cartilage constituent, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M16"><mml:mi>T</mml:mi><mml:mn fontstyle="italic">1</mml:mn></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M17"><mml:mi>T</mml:mi><mml:msup><mml:mrow><mml:mn fontstyle="italic">2</mml:mn></mml:mrow><mml:mrow><mml:mo>⁎</mml:mo></mml:mrow></mml:msup></mml:math> reflect actual tissue compositional features more closely than <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M18"><mml:mi>T</mml:mi><mml:mn fontstyle="italic">1</mml:mn><mml:mi>ρ</mml:mi></mml:math>.