Comparing Peira TM900 and caliper measurement for tumor volume calculation using a tumor volume formula.
TM900 3D measurement
3D Peira TM900 measurement
A direct 3D instrument, such as the Peira TM900, first captures a stereographic image of the tumor to reconstruct its topography and shape. Subsequently, a precise, real-time 3D volume of the xenograft is calculated based on this reconstructed geometry.
Because direct 3D measurement monitors changes across all three dimensions—namely, height, width, and length—it thereby produces more accurate and realistic volume data.
With constant width and length, the volume changes with the shape of the tumor. The obtained data include height and topography variations.
For a handheld, direct, 3D measurement instrument, such as the Peira TM900, the obtained value is independent from the angle or position of the instrument over the tumor. It will not affect the volume output.
The TM900 also stores an optical image in the measurement data base. These together with the tumor shape and all obtained data can easily be traced and consulted afterwards.
Caliper measurement
Using a tumor volume formula
When using a caliper, the operator first measures the width and length of the tumor and subsequently calculates the volume using a standard formula, such as π/6 x W x W x L or 1/2 x W x W x L. In doing so, this method inherently assumes that the tumor maintains a fixed, standardized geometric shape.
During caliper measurements, changes in tumor height are omitted; instead, only width and length dimensions affect the calculated volume. Consequently, critical information regarding true three-dimensional growth is lost.
As illustrated below, with the same measured values for width and length, the calculated volume does not change with the tumor shape.
For a caliper measurement, the angle at which it is held over the tumor will affect the obtained value, thus inducing an extra operator and manipulation sensitivity in the results. This effect is illustrated in the included video.
A caliper only digitizes the length and width of the tumor. Further geometrical or visual data are not stored simultaneously.
TM900 3D scanner data, Caliper Measurements and actual tumor volume
In general, caliper measurements are prone to inaccuracies, often resulting in considerable overestimations of actual tumor volumes. To demonstrate this, the following document compares caliper-based calculations with 3D scanner data and true volume estimates. Specifically, the comparative data show that measurements from the Peira TM900 and its successor, the Budetec TM900v2, are significantly more realistic and closely aligned with actual physical dimensions. The full document is available for download at:
https://tumorvolume.com/wp-content/uploads/2023/12/Calipers_TM900_Real.pdf
Furthermore, the following publication compares optical 3D measurements not only with formula-based caliper data but also with bioluminescence imaging:
https://www.biorxiv.org/content/10.1101/2024.05.07.592924v1
Measurement time
When comparing measurement efficiency, both the Peira TM900 and traditional caliper measurement require a similar amount of time. Specifically, operating the TM900 merely involves pressing the acquisition button; subsequently, images are saved and volume values are calculated almost instantly. In terms of usability, handling the handheld TM900 device is at least as effortless as holding a standard caliper. However, for both techniques, operators must develop proper dexterity and familiarize themselves with instrument manipulation. Ultimatelly, because a 3D measurement requires only one positioning over the tumor, whereas calipers one for width and one for length, there is a slight timing advantage in using the TM900. Subsequentially it also depends on the dexterity and experience of the operator.
Measurement method and operator dependency.
When using calipers, calculated volume data rely heavily on how the operator positions the tool over the xenograft. In contrast, a direct 3D measurement tool like the TM900 eliminates tool-positioning sensitivity; however, it cannot entirely rule out operator dependency. Specifically, both methods remain subject to variability introduced by animal handling. For example, different operators hold animals in distinct ways, causing variations in how the tumor is positioned or how prominent it appears under the skin. Furthermore, even a single operator may hold an animal differently across separate trials or time points. Consequently, tumor visibility and subcutaneous expression fluctuate regardless of whether calipers or the Peira TM900 are used. Nevertheless, because direct 3D scanners do not rely on manual tool placement, they exhibit less operator dependency overall, thereby reducing data spread—a conclusion consistent with the previously cited literature.