Clinical StudyA stereological study of MRI and the Cavalieri principle combined for diagnosis and monitoring of brain tumor volume
Introduction
Multiple techniques and measurements using radiological images are frequently carried out to obtain tumor volume values to assess tumor size.[1], [2], [3], [4] In addition to quantitative values obtained from measurements, volumetric ratios are also used for this purpose. The common aspect of these two approaches is that they assume that the 2-dimensional images directly reflect the real 3-dimensional properties of the tumor under investigation. However, the geometric features of 3-dimensional structures cannot be accurately judged from 2-dimensional images. Methods that rely solely on the properties of CT scans or MRI introduce serious bias in the resulting quantitative estimates.[5], [6], [7]
The definition of the tumor volume is a critical step in radiotherapy and surgical planning. Treatment design and its subsequent delivery are based on this step, and an error may lead to inaccurate delivery, which could reduce tumor control.8 Most physicians decide on the details of the treatment design after examination of 2-dimensional CT scans or MRI,[4], [9], [10] which is affected by their training and personal experience.
The aim of the present study is to describe the application of the Cavalieri principle, a stereological method that provides unbiased volume estimates, to assess tumor size using MRI without an over-projection/under-projection effect (over-/under-estimation).[6], [7], [11], [12] We present an MRI from an illustrative patient for this purpose. We utilized a previously described formula modified for MRI measurements to the eliminate over-estimation effects of imaging.13 The technique presented here can be applied easily in routine MRI since no additional equipment or experienced personnel are needed.
Section snippets
Measurement of brain tumor volume by the Cavalieri principle
In the Cavalieri principle, the structure of interest is cut in parallel plane sections from end to end, beginning at a randomly chosen starting point, with a series of parallel plane sections at a constant distance apart (Fig. 1A) that meet standard MRI techniques.[13], [14], [15], [16] The surface areas of the cut sections are estimated and multiplied by the mean section thickness to provide a volume of the examined object.[17], [18] The cut surface area of each section or slab is estimated
Results
The point counting procedure applied to preoperative images yielded 1357 points for the brain volume (a/p = 1.207 cm2; corrected for linear reduction) and 209 points for the tumor (a/p = 0.434 cm2; corrected for linear reduction). These data were used for volume estimations; hence, the total volume of the brain and the tumor were estimated at 1562.46 cm3 and 81.59 cm3, respectively.
Point counting on the postoperative images resulted in 1443 points (a/p = 1.141 cm2) for the brain and 232 points (a/p = 0.411 cm
Discussion
In most biological studies, researchers can only estimate the real quantity of what they are trying to find out, and a variety of methods are often in use. If the sampling or measuring methods are biased, assumption-based or wrong, the flaws might not be recognized until an unbiased, assumption-free gold standard study reveals the importance of an unbiased method to obtain quantitative results.[7], [23], [28] Stereology is used to evaluate unbiased properties of structures existing in three
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