Feature-invariant image registration method for quantification of surgical outcomes in patients with craniosynostosis: a preliminary study

New method for quantification of severity of isolated scaphocephaly linked to intracranial volume

PURPOSE

The aim is to implement Utrecht Cranial Shape Quantificator (UCSQ) for quantification of severity of scaphocephaly and compare UCSQ with the most used quantification method, cranial index (CI). Additionally, severity is linked to intracranial volume (ICV).

METHODS

Sinusoid curves of 21 pre-operative children (age < 2 years) with isolated scaphocephaly were created. Variables of UCSQ (width of skull and maximum occiput and forehead) were combined to determine severity. CI was calculated. Three raters performed visual scoring for clinical severity (rating of 6 items; total score of 12 represents most severe form). Pearson's correlation test was used for correlation between UCSQ and visual score and between both CIs. ICV was calculated using OsiriX. ICV was compared to normative values and correlated to severity.

RESULTS

Mean UCSQ was 22.00 (2.00-42.00). Mean traditional CI was 66.01 (57.36-78.58), and mean visual score was 9.1 (7-12). Correlations between both traditional CI and CI of UCSQ and overall visual scores were moderate and high (r = - 0.59; p = 0.005 vs. r = - 0.81; p < 0.000). Mean ICV was 910 mL (671-1303), and ICV varied from decreased to increased compared to normative values. Negligible correlation was found between ICV and UCSQ (r = 0.26; p > 0.05) and between ICV and CI and visual score (r = - 0.30; p > 0.05 and r = 0.17; p > 0.05, respectively).

CONCLUSION

Our current advice is to use traditional CI in clinical practice; it is easy to use and minimally invasive. However, UCSQ is more precise and objective and captures whole skull shape. Therefore, UCSQ is preferable for research. Additionally, more severe scaphocephaly does not result in more deviant skull volumes.

3D assessment of mandibular growth based on image registration: a feasibility study in a rabbit model

Background. Our knowledge of mandibular growth mostly derives from cephalometric radiography, which has inherent limitations due to the two-dimensional (2D) nature of measurement. Objective. To assess 3D morphological changes occurring during growth in a rabbit mandible. Methods. Serial cone-beam computerised tomographic (CBCT) images were made of two New Zealand white rabbits, at baseline and eight weeks after surgical implantation of 1 mm diameter metallic spheres as fiducial markers. A third animal acted as an unoperated (no implant) control. CBCT images were segmented and registered in 3D (Implant Superimposition and Procrustes Method), and the remodelling pattern described used color maps. Registration accuracy was quantified by the maximal of the mean minimum distances and by the Hausdorff distance. Results. The mean error for image registration was 0.37 mm and never exceeded 1 mm. The implant-based superimposition showed most remodelling occurred at the mandibular ramus, with bone apposition posteriorly and vertical growth at the condyle. Conclusion. We propose a method to quantitatively describe bone remodelling in three dimensions, based on the use of bone implants as fiducial markers and CBCT as imaging modality. The method is feasible and represents a promising approach for experimental studies by comparing baseline growth patterns and testing the effects of growth-modification treatments.

The relationship between scaphocephaly at the skull vault and skull base in sagittal synostosis

HYPOTHESIS

The skull vault is scaphocephalic in sagittal synostosis but little is known about the deformity at the skull base. If differential progressive deformity occurs between the vault and base, this might affect decision making regarding the timing of surgical intervention. We used 3-dimensional CT (3DCT) scans to compare deformity at the vault, base and posterior fossa in sagittal synostosis. Cephalic index (CI) was measured in 34 consecutive cases of isolated sagittal synostosis and 16 controls using predefined landmarks on the 3DCT volume data set. Planes were generated by a Vitrea™ workstation. Data were analysed by Student's t-test and Pearson coefficient.

RESULTS

Ratios of CI between the vault and base, and the vault and posterior fossa were significantly reduced in sagittal synostosis (p < 0.0001 and p = 0.0031) demonstrating a milder deformity at the base and posterior fossa. However there was strong positive correlation between CI at the vault and base (r = 0.77, p < 0.0001). We have therefore shown for the first time that the deformity at the base is less severe, but is still closely correlated with the vault in unoperated sagittal synostosis. This study provides a basis for future work analysing the progression of these deformities before and after surgery.

Mesh-based method for measuring intracranial volume in patients with craniosynostosis

PURPOSE

Craniosynostosis may lead to reduced intracranial volume (ICV) and disturb normal brain growth and development. Thus, ICV is an important parameter with respect to the surgical outcome. Current methods for ICV determination from computed tomography (CT) images have drawbacks. The aim of this study was to investigate the performance of the novel mesh-based method (MBM) for ICV determination with craniosynostosis patients.

METHODS

Twenty-two patients operated on for scaphocephaly were included in this study. ICVs from preoperative, one-week postoperative, and one-year postoperative CT images were measured with MBM. The level of agreement with the manual segmentation method (MSM) was determined for the measurements of preoperative and one-year postoperative datasets. Repeatability was determined with re-measurements of six datasets. Measurement time was recorded for MBM.

RESULTS

Mean [Formula: see text] preoperative ICV values were 895.0 [Formula: see text] 153.1 [Formula: see text] and 896.4 [Formula: see text] 147.2 [Formula: see text] as measured with MBM and MSM, respectively. Corresponding one-year postoperative values were 1,238.3 [Formula: see text] 118.7 [Formula: see text] and 1,250.1 [Formula: see text] 117.5 [Formula: see text]. The MBM allowed ICV determination from one-week postoperative datasets. Measurement time with MBM was 4 CONCLUSIONS: MBM is an efficient method for determining the ICV of craniosynostosis patients, allowing the measurement of skulls with bony defects. The repeatability and short measurement time of MBM are attributable to the user interference and assessment of the measurement process.