Computer-assisted alignment of standard serial sections without use of artificial landmarks. A practical approach to the utilization of incomplete information in 3-D reconstruction of the hippocampal region.

An algorithm for the alignment of stained serial sections without the support of artificial landmarks is described. Four-hundred-thirty serial sections of the rabbit hippocampal region were digitized, and computer-based alignment was performed without use of artificial markers, resulting in a consistent matrix. Following proper filtration, artificial sections were cut through the matrix. In a second experiment every second image was deleted and reconstructed by interpolation with a minor loss of biological information. In a third experiment every second image was deleted and the rest of the images were 'disordered', realigned and the missing planes reconstructed by interpolation. Under these circumstances the matrix was reconstructed with some loss of information. These results may widen the limits of 3-dimensional (3-D) reconstruction, as routine histological preparations normally include only every second or every third section without artificial landmarks.

Computer-assisted three-dimensional reconstruction of the hippocampal region based on serial sections.

A large series of rabbit hippocampal Neo-Timm stained sections were manually aligned, digitized, and by a modified median filtration noise reduced and reconstructed into a three-dimensional object. From the presented simulated grey tone cuts of this object, the reader may assemble a rabbit hippocampal model, that spatially illustrates its anatomy.

Propagation speed of sound assessment in the layers of the guinea-pig esophagus in vitro by means of acoustic microscopy.

The study's purpose was to evaluate the propagation speed of sound in the tissue layers of the esophagus at various mechanical loadings. Scanning laser acoustics microscopy was applied for the estimation of the propagation speed in the mucosa-submucosa and muscle layers of guinea-pig esophagus in vitro (n = 26). The propagation speed in the esophagus was determined in the no-load state with all external forces removed, and in the distended and zero-stress states. The zero-stress state was obtained by cutting the esophageal rings radially. The propagation speed in the no-load state differed significantly (p < 0.001) between the muscle layer (median 1740, quartiles 1735-1746 m/s) and the mucosa (1607, 1605-1609 m/s). In the distended state the propagation speed in the muscle layer decreased significantly (p < 0.001) to 1673 (1666-1681) m/s while it did not change significantly in mucosa (1602, 1600-1607 m/s). When compared to the no-load state, the propagation speed in the zero-stress state in the muscle layers decreased to 1624 (1615-1636) m/s (p < 0.001) and in mucosa to 1584 (1566-1603) m/s (p < 0.001). In conclusion, the esophagus is a composite structure with heterogeneous propagation speed characteristics. Furthermore, the mechanical loading state must be considered in esophageal ultrasound studies.

Determination of biomechanical properties in guinea pig esophagus by means of high frequency ultrasound and impedance planimetry.

Impedance planimetry and high-frequency ultrasound were used to determine circumferential stress and strain from measurements of luminal cross-sectional area and wall thickness during balloon distension of the guinea pig esophagus in vitro (N = 30). The excised esophagus was mounted on two plastic tubes in an organ bath containing oxygenated calcium-free Krebs-Ringer solution with 10(-2) M MgCl2 to abolish smooth muscle contractile activity. One of the plastic tubes was movable in order to stretch the esophagus longitudinally by 15% (elongated state). The impedance planimetry probe was placed with the balloon inside the lumen of the esophagus. A 20-MHz ultrasound transducer was mounted above the esophagus and provided scans in the transverse and longitudinal directions. The luminal cross-sectional area at the highest applied pressure of 2.9 kPa was 13.3 +/- 0.3 mm2 in the resting state. In the elongated state the luminal cross-sectional area at the highest pressure was 12.5 +/- 0.1 mm2 (P < 0.02). The wall thickness decreased from 990 +/- 21 microm at 0 kPa to 640 +/- 9 microm at 2.9 kPa at in vitro length. In the elongated state, the values were 940 +/- 32 microm to 480 +/- 13 microm (P < 0.01). The stress-strain relation was exponential (sigma = alpha(ebetaepsilon - 1), r2 > 0.98, P < 0.01). The circumferential elastic modulus calculated at a Green strain of 0.95 was 44.5 +/- 10.5 kPa in the in vitro state and 81.7 +/- 13.1 kPa in the elongated state. The elastic modulus differed between the resting and elongated states (P < 0.02).

Seven-channel digital telemetry system for monitoring and direct computer capturing of biological data.

A seven-channel telemetry system for collection and display of biological data is presented. The system can amplify bioelectrical signals in the range of 2 microV to 200 mV and has a bandwidth of 0.1-80 Hz. After multiplexing, the signals are digitized with a resolution of 8 bits. The data are frequency modulated directly on a VHF transmitter. After receiving the data on a VHF receiver, they are routed directly to the RS232 input connector on the PC. Thereby the advantage of direct communication between the transmitter and the PC can be utilized. Expensive analog equipment is avoided and display of the signals on the PC screen as well as signal analysis can be performed. The system has been tested and was found to be stable and highly reliable.

Small intestine wall distribution of elastic stiffness measured with 500 MHz scanning acoustic microscopy.

Obtaining data relating intestinal mechanical properties and histology is a step towards the next level in the hierarchy of structure of living tissue, and may provide new insight into the mechanisms of intestinal function and disease such as obstruction. Due to lack of methodology, however, such data are currently sparse. Scanning acoustic microscopy (SAM) can measure the propagation speed of sound (C) and the acoustic impedance (Z) with micrometer resolution in tissue. By use of elementary theory of elasticity, the elastic stiffness (c11) can be computed from C and Z. We used 5-microm-thick transverse sections of ethanol treated guinea pig small intestine as the experimental model and measured the distribution of C and Z across the intestinal wall using SAM at 500 MHz. The individual layers mucosa, submucosa, and circular and longitudinal muscle were discerned with ease in the images and varied significantly with respect to both C and Z in most cases. The measured values (median values) of C ranged from 1550 to 1669 m s(-1), and Z ranged from 2.10 to 2.60 MPa s m(-1). c11 differed between all layers ranging from 3.25 to 4.27 GPa with the following sequence of magnitude: circular muscle >submucosa>mucosa>longitudinal muscle (p<0.001). In conclusion, we provided the first microscale mechanical data relating to the histological layers of the small intestine.

Left ventricular opacification after intravenous injection of Albunex. The effect of different administration procedures.

A clinical study has been performed to investigate the influence of different administration procedures on the degree of contrast enhancement of the left ventricle. The administration variables assessed included Albunex injection rate, arm position, flushing rate and flushing fluid. Twenty-four healthy male volunteers were included. Compared to an injection rate of 1 ml/sec an injection rate of Albunex of 2 ml/sec caused an earlier appearance of contrast in the right ventricle (1 heart beat), whereas transpulmonary passage was not influenced. Horizontal arm position caused a delay in time to peak intensity of 2 to 3 heart beats in both systole and diastole as compared to elevated arm position. Injection rate of 1 ml/sec compared to 2 ml/sec caused a higher peak intensity and mean area under the curve and a longer mean time to peak intensity and transit time. Differences varied from 6 to 230 grey level units out of mean values of 2500. All the observed differences were small and thus probably of no clinical importance. The present study indicates that improvements in the pressure stability characteristics of the albumin microspheres in Albunex have been achieved. This implies that a simple administration procedure can be used. It is recommended that the contrast agent, after resuspension, is injected through a three-way stop cock cannula, followed by 10 ml of saline for flushing. The cannulas or syringes used should be no smaller than 20 G. The injection rate should be 1-2 ml/sec, depending on the diameter of the cannula. By using this procedure, a reliable transpulmonary passage and left ventricular opacification may be obtained.