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 |