[Periodic alternating nystagmus in familial congenital cerebellar ataxia].

We noted periodic alternating nystagmus (PAN) in two patients (mother and daughter) who were diagnosed as familial congenital cerebellar ataxia. The mother was 51-year-old and her PAN had about 4 minutes cycle. During eye closure there was a deviation of arms and trunk parallel to the direction of the slow phase of nystagmus. Vestibular stimulation during rotatory and caloric tests disclosed enhanced vestibulo-ocular reflexes, changes of direction and prolonged cycle of PAN. The patient had no visual suppression during caloric stimulation. The daughter was 14-year-old and although she had no spontaneous PAN she had latent PAN by showing changes of direction of nystagmus during the caloric stimulation. She had also no visual suppression during caloric stimulation. From these results the mechanism of PAN could be attributed to the periodic hyperfunction of vestibular nuclei caused by reduced suppression from cerebellar uvula and nodulus.

[Count rate characteristics and count loss correction of Positologica II: a whole body positron emission tomograph].

This paper describes evaluation and correction of count rate characteristics of POSITOLOGICA II, a multi-slice whole body positron emission tomography system. The present study was performed using three phantoms; a 5 cm inner diameter, water-filled lucite cylinder, a 20 cm inner diameter, water-filled lucite cylinder and a chest phantom. After injection of high activity (about 1.85 GBq (50 mCi] of 13N ammonia into each phantom, rates of true coincidence, random coincidence and single photon detections were measured during decay of the isotope through more than two orders of magnitude of activity. At very high levels of activity, count rate characteristics of the system were saturated and limited to 660 kcps of total coincidence rate, which was the sum of rates in on-time and off-time windows, by the FIFO (first-in first-out) output frequency. Below those levels of activity the relationship between count loss and true coincidence rate was not unique but depended on the phantom configurations, suggesting that count loss correction using the above relationship was inadequate for quantitative study. However, the relationship between count loss and single rate was almost independent of the phantom configurations. Thus in conclusion count loss could be corrected using single rate for POSITOLOGICA II. A practical method of count loss correction was also proposed.