David C. Hemmy

Three Dimensional Imaging in Medicine

Three dimensional reconstruction of CT scan data is available to surgeons. The authors discuss the relative merits and disadvantages of this new method of presentation of anatomical data. Recommendations are made for future development and implementation.

Clinical Outcome of the Modified Pi-plasty Procedure for Sagittal Synostosis

The aim of the study was to evaluate the modified pi-plasty procedure for the treatment of sagittal synostosis, assessing the issues of safety, complications, morphological outcome, and degree of parental satisfaction. A retrospective evaluation of 110 patients with nonsyndromal single suture sagittal synostosis operated on with the modified pi-plasty procedure was undertaken. Cephalometric radiographs were obtained preoperatively and postoperatively at ages 3 and 5 years in three standardized projections. The Cephalic Index and the Axial Width Ratio were determined and used as objective outcome measures. An evaluation of the radiographic digital markings was carried out using a Beaten Copper Score. A parental questionnaire was used to obtain a subjective esthetical outcome assessment. The patient population consisted of 76% boys and 24% girls with a 20% incidence of a positive familial history of craniosynostosis. The mean age at surgery was 7.73 months. Morbidity from the procedure was minimal and there were no mortalities. The Cephalic Index changed from a mean preoperative value of 65% to a postoperative mean value of 72% (P = 0.00004). The mean Axial Width Ratio changed from a preoperative 80% to 72% at the 3-year evaluation (P = 0.00029). The Beaten Copper score changed from a mean preoperative value of 2.35 to 5.42 postoperatively at 3 years (P = 0.00001). The response rate to the questionnaire was 86%, and there were significant postoperative improvements in all studied aspects of the skull shape. The modified pi-plasty is a safe technique, and it induces significant objective changes in skull morphology toward normality. It also yields a high degree of parental satisfaction with regard to aesthetic outcome, as evaluated by a written questionnaire.

Evoked Potentials in Experimental Myelopathy

Evoked potentials recorded from the cerebral cortex and spinal cord secondary to peripheral stimulation are reversibly reduced in amplitude by both pathologic distraction and pathologic flexion of the vertebral column. While the cerebral responses are lost within two minutes after complete occlusion of the ascending aorta, the responses recorded from the spinal cord persist without change for approximately ten minutes and then gradually disappear. During the first few minutes after aortic occlusion, changes produced by spinal distraction and spinal flexion are indistinguishable from those produced when the same maneuvers are made with the aorta patent. The responses mediated by dorsal columns and corticospinal tracts are affected in the same way by flexion and distraction, suggesting that somatosensory evoked potential recordings should be a reliable means of detecting spinal cord dysfunction during surgical procedures affecting the spinal cord. It may also be possible to differentiate a mechanical from a vascular insult by the time required for the evoked potential to become abnormal following a particular surgical maneuver.

A Pentium personal computer-based craniofacial three-dimensional imaging and analysis system.

&NA; Personal computer (PC)‐based computing is now ubiquitous in common consumer applications. Although PCs have equaled or surpassed engineering workstations in basic computing power and economy, there is still strong workstation dependency for imaging applications. This article demonstrates that a complete system, based on a Pentium PC (Intel Corporation, Santa Clara, CA) and readily available and inexpensive software, can be built very economically for effective execution of most of the commonly used three‐dimensional imaging operations. For the craniofacial application, the Pentium system offers a twofold speed advantage over a Sparc 20 system using similar three‐dimensional processing software. The Pentium system allows interactive fuzzy volume rendering, and manipulation and analysis of complex hard and soft‐tissue structures.

Traumatic facial injuries with steering wheel loading

This study was conducted to evaluate the biomechanics of facial fractures caused by steering wheel loading. Twelve intact fresh human cadaver heads were impacted onto standard or energy-absorbing steering wheels with a custom-designed and validated vertical-drop apparatus. Either zygoma was impacted once at a velocity of 2.0-6.9 m/s. The specimens were oriented to permit a direct comparison between pretest and posttest radiography, and two-dimensional and three-dimensional CT images. Bone mineral content was determined, and biomechanical forces, accelerations, and deformations were recorded. More severe fractures were associated with higher forces on the zygoma. With increasing velocities, fractures initiated at the zygomatic region propagated to other unilateral regions such as the mandible and orbit or to the contralateral side. Less facial trauma was observed with energy-absorbing steering wheels compared with standard wheels at similar impact velocities. Bone mineral content did not correlate well with specimen age or with fracture severity. Clinically significant fractures were identifiable on 3-D CT images. The flexibility of 3-D CT in evaluating the spatial extent of facial abnormalities in different orientations may have significant impact in planning surgical procedures.

Physiological and Histological Effects of Cerebellar Stimulation

Cerebellar implants have been placed in 62 patients with postoperative follow-up of 4 months to 3 years. Initially currents were applied through electrodes of alternate polarity on the superior surface of the cerebellar hemispheres and subsequently through negative electrodes on the superior surface to positive electrodes on the posterior surface. The amount of current required for clinical improvement was approximately the same as that required to significantly reduce the amplitude of the somatosensory evoked potential. The clinical and electrophysiological effects were proportional to the intensity of current and to the number of electrodes through which the currents were applied. Currents applied through the cerebellum were more effective than those confined near the cerebellar surface. Histological examination of the cerebellum from the chimpanzees and from 1 patient who died of causes unrelated to stimulation failed to demonstrate any evidence of neuronal damage related to application of current.

Cerebellar Implant Studies

Electrical currents were applied to the cerebellum of anesthetized monkeys using techniques similar to those employed in human cerebellar electrode implant systems. Alterations in the bloodbrain barrier were not observed. Histological damage, when present, appeared secondary to mechanical injury rather than to application of current. Measurement of current density in the monkey and human cerebellum indicated that with the electrode configuration employed, most of the current is retained in the vicinity of the electrodes. In human patients with spasticity and dyskinesia, application of current through implanted cerebellar electrode units relieves spasticity and also has been associated with reduction of somatosensory evoked potential amplitude. The amount of current required for clinical improvement and for alteration of evoked potential amplitude has remained stable in all patients, even those followed for more than a year. These observations suggest that the methods described do not produce appreciable cerebellar damage.

Evaluation of Electrode Configurations in Cerebellar Implants

Capacitively coupled currents of 100 Hz, 0.25 msec duration, were applied to multielectrode arrays implanted upon the superior and posterior surfaces of the chimpanzee cerebellum. The current required for 90% reduction in the amplitude of the evoked potential was inversely proportional to the number of electrodes upon the cerebellar surface. A study of various waveforms showed that z Hz, 0.25 msec pulse duration is near optimal for reduction of amplitude of the somatosensory evoked potential. The current densities per electrode were 5--11 mA/cm2 with a charge per pulse of 0.04--0.08 muC in humans with 15--20 electrodes on each superior surface and 10 electrodes on each posterior cerebellar surface.

Fuzzy connected object rendering

There are many situations in 3D imaging applications wherein object and non-object regions with identical image properties are situated in close proximity. Although the commonly used opacity functions are adequate in capturing object gradation in these situations, the non-object regions obscure the objects of interest in volume renditions based on these opacity assignments. These obscurations cannot be removed using simple techniques except by manually masking them out. We present a method based on fuzzy connectedness principles which effectively removes the obscuration automatically. The methods are illustrated using craniomaxillofacial CT patient data for separating thin bones from skin and muscle, and muscle from skin and bone boundary. The resulting remarkable clarity of renditions are illustrated.

Gas myelography in spinal cord injury.

Using polytomographic techniques, gas myelography was performed in 162 patients with post-traumatic neurologic deficit. The type, extent, and location of lesions were easily demonstrated, allowing adequate preoperative surgical planning. In cases in which expected neurologic improvement did not follow surgery, postoperative myelography provided information so that remedial measures could be taken. No neurologic deterioration was noted in any of the patients and furthermore, arachnoiditis, which may accompany positive contrast myelography, has not been detected in any of the patients in the series reported.