Comments(2)Solid Methodology: A reply to comment by Dr. JordanHollis King
(17 September 2009) The Osteopathic Research Center The authors appreciate the concern expressed by Dr. Jordan and the opportunity to respond. Dr. Jordan is correct in that his question could have been addressed in the article and rendered his comment unnecessary. The issue raised is technical and based on the threshold settings for ImageJ analysis. The methodology employed in the present study used settings that focused analysis only on the bone, not any gray area outside, or inside the bone. The threshold settings used on all 160 individual images allowed analysis only on dense boney structure. The link www.cranialacademy.org/MRIimage.tif provides access to the actual MRI image from which figures 3 and 4 were generated to illustrate the steps in the ImageJ analysis. The outer white ovoid is bone, and all dimensions analyzed were based on the outer edge of the white bone image, which were similar but not exactly the same outer dimensions illustrated in figures 3 and 4. The only difference being the threshold settings which allowed the assessment of the outer bone surface. Competing interests No competing interests Have something to say? Post a comment on this article! |
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Serious flaws in study
Theodore Jordan (12 September 2009) Dept Med Ed, Doctors Hospital, Columbus, OH USA
The study entitled “Assessment of calvarial structure motion by MRI”, claims to have measured a change in calvarial transverse sectional area over time, and is interpreted to represent a change in intracranial fluid volume changes. However, this study has serious flaws in both its design and interpretation. It appears that all measurements were made of the outer most diameter of the tissues of the scalp, and this measurement implies nothing about intracranial dynamics.
The authors could have been clearer regarding the exact parameters measured. Figure 3 is an example of the MRI image after adjusting grayscale threshold to represent only the two shades of gray and black. The brain matter is represented in gray. The bone of the clavarium is represented as the surrounding black, and surrounding the bone is another area of gray representing the tissues of the scalp. By carefully looking at the very outer pixels of figure 3, it appears that figure 4 is a pixilated representation of the very outer border of the gray-scale scalp tissues of figure 3. Therefore, figure 4 represents neither the inner, nor the outer border of the calvarial bone as imaged on MRI, but rather the very outer border of the tissues of the scalp.
If the above interpretation of the measured parameters is correct, then this study succeeds in demonstrating that the outer diameter of the scalp may expand and contract over time. Since the late nineteenth century, it has been known that there are vasomotor waves in cutaneous tissue, which swell and recede in response to changes in blood volume. These are known as third-order waves, or Traube-Hering-Mayer waves. This phenomenon has later been associated with the rhythmic changes of the sympathetic nervous system tone and with blood flow dynamics associated with parasympathetically mediated heart rate variability [1].
In a study using laser flowmetry to measure blood flow dynamics scalp in adults, the rhythmic expansion and contraction of the scalp, known to osteopaths as the ‘cranial rhythmic impulse’ (CRI) was further correlated to be essentally synchronous with the third-order vasomotor phenomenon [2].
It is of no surprise that the outer diameter of the scalp changes over time. To assume that this represents changes of intracranial dynamics, one would have to assume that the thickness of the scalp does not change. It is unclear why the authors chose to use the outer most border of the MRI scan for this study (representing outermost scalp), rather than using the inner table of the bone of the skull for pixillation and measurement.
The conclusions that this study “is suggestive of inherent motion in calvarial structure”, and that “the total intracranial area appeared to expand and recede” are invalid conclusions and not supported by the methodology used in this study.
Respectfuly,
Theodore Jordan, DO C-NMM
Dept. Medical Education
Doctors Hospital, Columbus, OH
[1] Myers CW et al. A model for the genesis of arterial pressure Mayer waves from heart rate and sympathetic activity. Autonomic Neurosci: Basic and Clin 2001;91:62-75
[2] Nelson et al. Cranial rhythmic impulse related to the Traube-Hering-Mayer oscillation: comparing laser-Doppler flowmetry and palpation. JAOA 2001;101:163-73
Competing interests
none
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