Anechoic sphere phantoms for estimating 3-D resolution of very-high-frequency ultrasound scanners

Two phantoms have been constructed for assessing performance of high-frequency ultrasound imagers. They also allow for periodic quality assurance tests and training technicians in the use of higher-frequency scanners. The phantoms contain eight blocks of tissue-mimicking material; each block contains a spatially random distribution of suitably small anechoic spheres having a small distribution of diameters. The eight mean sphere diameters are distributed from 0.10 to 1.09 mm. The two phantoms differ primarily in terms of the frequency dependence of the backscatter coefficient of the background material. Because spheres have no preferred orientation, all three (spatial) dimensions of resolution contribute to sphere detection on an equal basis; thus, the resolution is termed 3-D. Two high-frequency scanners are compared. One employs single-element (fixed focus) transducers (25 and 55 MHz), and the other employs variable focus linear arrays (20, 30, and 40 MHz). The depth range for detection of spheres of each size is determined corresponding to determination of 3-D resolution as a function of depth. As expected, the single-element transducers are severely limited in useful imaging depth ranges compared with the linear arrays. In this preliminary report, only one human observer analyzed images.

Thyrotropin-secreting pituitary tumours: significance of “atypical adenomas” in a series of 10 patients and association with Hashimoto thyroiditis as a cause of delay in diagnosis

Background:

Thyrotropin-secreting adenomas (TSH-As) are rare and, according to the World Health Organization criteria (WHO 2004), a significant proportion of them present features of atypical adenomas at the time of diagnosis.

Aims:

To determine the frequency of “atypical adenomas” and the significance of this definition as regards follow-up. To investigate their possible association with Hashimoto thyroiditis, leading to a delay in diagnosis.

Methods:

Case notes for patients who underwent trans-sphenoidal surgery between 1992 and 2006 were retrieved. Follow-up ranged from 6 to 180 months.

Results:

Ten cases of TSH-As out of 908 pituitary adenomas were selected. Before surgery, eight patients had hyperthyroidism, one was euthyroid and another one showed hypothyroidism associated with Hashimoto thyroiditis. All cases were macroadenomas; six of them were invasive. Three cases met the criteria for classification as atypical. In none of the cases, including the three “atypical adenomas”, were clinical or radiological signs of recurrence observed.

Conclusions:

The three cases with features of atypical adenoma did not recur or metastasise, suggesting that, at least in the present series, a strict relationship between the morphological criteria for diagnosing atypical adenomas and biological behaviour may be sometimes lacking. Furthermore, the casual association of TSH-As with Hashimoto thyroiditis may led to an adjunctive delay in diagnosis, because of low thyroid hormone levels.

An accelerator for neural networks with pulse-coded model neurons

The labeling of features by synchronization of spikes seems to be a very efficient encoding scheme for a visual system. Simulation of a vision system with millions of pulse-coded model neurons, however, is almost impossible on the base of available processors including parallel processors and neurocomputers. A "one-to-one" silicon implementation of pulse-coded model neurons suffers from communication problems and low flexibility. On the other hand, acceleration of the simulation algorithm of pulse-coded leaky integrator neurons has proved to be straightforward, flexible, and very efficient. Thus we decided to develop an accelerator for a special version of the French and Stein neurons with modulatory inputs which are advantageous for simulation of synchronization mechanisms. Moreover, our accelerator also provides a Hebbian-like learning rule and supports adaptivity. Up to 128 K neurons with a total number of 16 M freely allocatable synapses are simulated within one system. The size of networks, however, is not at all limited by these numbers as the system may be arbitrarily expanded. Simulation speed obviously depends on the number of interconnections and on the average activity within the network. In the case of locally interconnected networks for simulation of vision mechanisms there is only a very low percentage of simultaneously active neurons: stimuli are not simultaneously presented in all orientations and at all positions of the visual field. In these cases our accelerator provides close to real-time behavior if one second of a biological neuron is simulated by 1000 time slots.