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Table 1 Summary of techniques to measure the dimensions and geometries of soft tissues and their clinical value

From: A review of methods to measure tendon dimensions

Technique Papers Advantages Disadvantages Clinical value
Anthropomorphic correlations [62, 74, 75, 85] • Simple
• Fast
• Limited reliability
• Inherent errors due to assumptions
• Not truly patient-specific
• Lack of quality physical measurements for comparison
Limited clinical usefulness due to assumptions and low reliability
Ruler [76] • Simple
• Fast
• Unable to measure two- or three-dimensional geometry Clinically useful due to simplicity
Computed tomography (CT) [63, 67, 135, 136] • Readily available diagnostic imaging technique
• Non-contact
• Non-invasive
• Three-dimensional
• Poor discrimination of soft tissues
• Radiation dose
• Lack of quality physical measurements for comparison
Limited clinical usefulness due to poor discrimination of soft tissues
Computed tomography with contrast [68, 69] • Improved differentiation of soft tissues
• Non-contact
• Non-invasive
• Three-dimensional
• Limited to ex vivo evaluations
• Potential deformation of tissue
• Poor discrimination of soft tissues
• Radiation dose
Limited clinical usefulness due to difficulty applying contrast agents
Magnetic resonance imaging (MRI) [61, 62, 70,71,72,73,74,75,76,77,78,79,80,81,82,83,84, 137, 138] • Readily available diagnostic imaging technique
• Able to differentiate soft tissues
• Image quality can be improved with digital post-processing
• Safe
• Non-contact
• Non-invasive
• Three-dimensional
• Expensive
• Slow
• Lack of robust methodologies
• Conflicted reports of accuracy and reliability
• May not adequately resolve paratenon
• Lack of quality physical measurements for comparison
Clinically useful due to clear differentiation of soft tissues
Ultrasound, 2D (2DUS) [39, 45, 66, 73, 78, 79, 85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115] • Readily available for diagnostic imaging technique
• Safe
• Fast
• Non-invasive
• Inexpensive
• Able to differentiate soft tissues
• Two-dimensional
• Conflicted reports of accuracy and reliability for deep tendons
• Results dependent on operator, pressure, position, and orientation
• Lack of quality physical measurements for comparison
• Unable to detect paratenon
• Requires contact
Clinically useful for superficial tendons
Ultrasound, 3D (3DUS) [117,118,119,120,121] • Accurate
• Reliable
• Repeatable
• Reduced operator-, position-, and orientation-dependency
• Safe
• Fast
• Non-invasive
• Three-dimensional
• Able to differentiate soft tissues
• Unable to detect paratenon
• Requires contact
• Pressure dependency
High clinical usefulness for superficial tendons
Sectioning [27, 124, 125] • Accurate
• Repeatable
• Can be reconstructed to three-dimensional
• Destructive Low clinical usefulness due to destructive nature
By estimation [126] • Simple
• Fast
• Inherent errors due to shape assumptions
• Does not capture geometry
• Affected by measurement technique (e.g. ruler)
Clinically useful for comparative measurements
Area micrometry [126,127,128] • Simple
• Fast
• Repeatable
• Underestimates area
• Contact
• Does not capture geometry
Clinically useful for comparative measurements
Casting [129,130,131] • Accurate
• Reliable
• Repeatable
• Three-dimensional
• Ability to revisit measurements
• Slow
• Contact
• Requires tissue to be isolated
• Unable to visualise internal structures
Clinically useful for some tissues, particularly resected tissues
Shadow amplitude [126] • Accurate
• Non-contact
• Poor repeatability
• Unable to visualise internal structures
Limited clinical usefulness
Laser micrometry [4, 59, 60, 64, 132, 134, 139, 140] • Fast
• High accuracy
• Repeatable
• Reliable
• Non-contact
• Two-dimensional
• Affected by specimen geometry, concavities, opacity, reflectivity, and orientation
• Unable to visualise internal structures
Limited to external and ex vivo measurements
Laser scanning [142] • Fast
• High accuracy
• Repeatable
• Reliable
• Non-contact
• Three-dimensional
• Affected by specimen geometry, concavities, surface refraction, alignment of sample, opacity, reflectivity, and orientation
• Limited viewing window for three-dimensional reconstruction
• Unable to visualise internal structures
Clinically useful for 3D surface measurements. Limited to external and ex vivo tissues
Photogrammetry [143] • High accuracy
• Repeatable
• Reliable
• Non-contact
• Three-dimensional
• Photorealistic reconstruction
• Affected by concavities
• Unable to visualise internal structures
Clinically useful for 3D surface measurements. Limited to external and ex vivo tissues
Structured white light (SWL) [144,145,146] • Fast
• High accuracy
• Repeatable
• Reliable
• Non-contact
• Three-dimensional
• Photorealistic reconstruction
• Affected by small concavities
• Unable to visualise internal structures
Clinically useful for 3D surface measurements. Limited to external and ex vivo tissues
Digital image correlation (DIC) [147,148,149,150,151,152,153,154,155] • Fast
• High accuracy
• Repeatable
• Reliable
• Non-contact
• Three-dimensional
• Requires sample preparation
• Affected by small concavities
• Unable to visualise internal structures
Clinically useful for 3D surface and strain measurements. Limited to external and ex vivo tissues