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Table 3 Different measurement techniques have advantages and disadvantages

From: Methods for verification of 3D printed anatomic model accuracy using cardiac models as an example

Technique Overview Advantages Disadvantage
Manual measurements Measuring instruments such as digital calipers are used to physically measure features. • Cost effective
• Straightforward technique
• Can be difficult to access internal structures
• Overtightening of calipers can deform flexible models
• Non-linear measurements such as perimeters cannot be accomplished with calipers
Digital photographic measurements The process requires photographing a feature of interest with a reference scale in the same plane. The scale consists of an object of known size which can be used to determine the pixel/dimension ratio. The ratio is then used to measure the feature of interest. • Simple set-up
• Cost effective
• Nonlinear measurements are possible, such as perimeter measurements
• Differences in illumination can introduce error
• Reference feature and/or scale must be on the same plane as the feature of interest (or the difference must be accounted for)
3D Scanning This method uses lasers or structured light to collect information about an object’s surface. This information is assembled as a point cloud (digital 3D coordinates) which can be translated into a digital 3-dimensional surface model of the structure. • High resolution
• portable
• Scanners can be expensive: Optical pattern projection systems range from $1000- $100,000. Laser scanning systems range from $25,000 - $1,000,000.
• There is a learning curve for proper scanning technique
• Clear and reflective model surfaces can be challenging to scan
Photogrammetry This method uses digital images of a 3D object, taken at different angles, to generate a 3D reconstruction using image registration. The method has become very popular in the recent years thanks to the widespread implementation of high-resolution cameras in mobile devices. • Cost effective • Requires understanding of image processing principles
• Requires familiarity with an array of software packages (e.g., Visual SFM, Meshlab)
CT scanning Computed tomography uses x-rays to produce 2-dimensional images that are stacked to produce a 3D volume. • Can measure geometry of internal structures
• Fast and accessible in most hospitals
• Expensive
• Requires image registration to original DICOM