Characterisation of coronary atherosclerotic morphology by spectral analysis of radiofrequency signal: in vitro intravascular ultrasound study with histological and radiological validation.

OBJECTIVE: To determine whether spectral analysis of unprocessed radiofrequency (RF) signal offers advantages over standard videodensitometric analysis in identifying the morphology of coronary atherosclerotic plaques. METHODS: 97 regions of interest (ROI) were imaged at 30 MHz from postmortem, pressure perfused (80 mm Hg) coronary arteries in saline baths. RF data were digitised at 250 MHz. Two different sizes of ROI were identified from scan converted images, and relative amplitudes of different frequency components were analysed from raw data. Normalised spectra was used to calculate spectral slope (dB/MHz), y-axis intercept (dB), mean power (dB), and maximum power (dB) over a given bandwidth (17-42 MHz). RF images were constructed and compared with comparative histology derived from microscopy and radiological techniques in three dimensions. RESULTS: Mean power was similar from dense fibrotic tissue and heavy calcium, but spectral slope was steeper in heavy calcium (-0.45 (0.1)) than in dense fibrotic tissue (-0.31 (0.1)), and maximum power was higher for heavy calcium (-7.7 (2.0)) than for dense fibrotic tissue (-10.2 (3.9)). Maximum power was significantly higher in heavy calcium (-7.7 (2.0) dB) and dense fibrotic tissue (-10.2 (3.9) dB) than in microcalcification (-13.9 (3.8) dB). Y-axis intercept was higher in microcalcification (-5.8 (1.1) dB) than in moderately fibrotic tissue (-11.9 (2.0) dB). Moderate and dense fibrotic tissue were discriminated with mean power: moderate -20.2 (1.1) dB, dense -14.7 (3.7) dB; and y-axis intercept: moderate -11.9 (2.0) dB, dense -5.5 (5.4) dB. Different densities of fibrosis, loose, moderate, and dense, were discriminated with both y-axis intercept, spectral slope, and mean power. Lipid could be differentiated from other types of plaque tissue on the basis of spectral slope, lipid -0.17 (0.08). Also y-axis intercept from lipid (-17.6 (3.9)) differed significantly from moderately fibrotic tissue, dense fibrotic tissue, microcalcification, and heavy calcium. No significant differences in any of the measured parameters were seen between the results obtained from small and large ROIs. CONCLUSION: Frequency based spectral analysis of unprocessed ultrasound signal may lead to accurate identification of atherosclerotic plaque morphology.

Characterisation of red and white thrombus by intravascular ultrasound using radiofrequency and videodensitometric data-based texture analysis.

Visual assessment of intravascular ultrasound (IVUS) video images cannot reliably identify thrombus. We examined if texture analysis of radiofrequency (r.f.) data or videodensitometric data (VD) could distinguish thrombi of different ages and cell compositions. Whole human blood (red clot = RC), platelet-rich plasma (white clot = WC) and plasma (n = 6/group) were imaged at 4 and 24 h with 30 MHz IVUS transducers. At 4 h, VD- and r.f.-based analyses revealed significant differences between RC and WC with variance (VD red 26.4 +/- 2.5, white 33.9 +/- 7.8; r.f. red 1.4 +/- 0.5, white 4.9 +/- 1.3), kurtosis (VD red 0.29 +/- 0.9, white 0.23 +/- 0.3) and skewness (VD red 0.23 +/- 0.13, white 0.35 +/- 0.52; r.f. red 0.06 +/- 0.01, white -0.06 +/- 0.05). Also mean grey-level from both data sets was higher in RC (VD 134.8 +/- 18.0; r.f. -13.3 +/- 1.2) than in WC (VD 105.3 +/- 17.4, r.f. 16.5 +/- 2.2) (p < 0.01). With increasing time, variance increased in WC (5.5 +/- 1.5 at 24 h) and decreased in RC (0.9 +/- 0.3.3 at 24 h). The more heterogeneous structure of WC may be distinguished from that of RC using texture analysis of either VD or r.f.-signals.

Characterisation of atherosclerotic plaque by spectral analysis of intravascular ultrasound: an in vitro methodology.

Raw 30-MHz intravascular ultrasound data have been captured from postmortem coronary arteries (n = 4) to develop radio frequency analysis techniques for the characterisation of atherosclerotic plaque. Digitised data acquired from positions (n = 8) within diseased sections of artery were compared with the corresponding histology and radiology. Scan-converted images were used to locate regions of interest (ROI = 33) within areas of tissue composition: loose fibrotic tissue (LFT), dense fibrotic tissue (DFT) and calcium (CA). A range of parameters was extracted from the normalised power spectrum of each ROI within the bandwidth 17-42 MHz. Significant discrimination between LFT/DFT and between LFT/CA was provided by maximum power and spectral slope (dBMHz-1). However, the greatest discriminative power was given by the y-axis (0 Hz) intercept of the spectral slope: LFT/DFT (p = 0.001); LFT/CA (p = 0.0001); and DFT/CA (p = 0.089).

A study of the quantitative and qualitative impact of catheter shaft angulation in a mechanical intravascular ultrasound system.

Nonuniform rotation of mechanical intravascular ultrasound transducers may give rise to a geometric distortion of the ultrasound image known as the rotation angle artefact. This investigation studied the influence of different degrees and combinations of catheter shaft angulation on image morphology and the quantitative impact of the artefact using a circular perspex phantom and 3.5 F, 30 MHz Boston Scientific "Sonicath" catheters connected to a Hewlett Packard Sonos intravascular scanner. Major and minor diameters, cross-sectional area and circumference of the phantom lumen were measured and a "distortion index" calculated. Visually apparent geometric distortion was graded from 1 (absent) to 4 (severe). As expected, eccentric transducer location was associated much more frequently with identifiable distortion (70%) than was a concentric location (6%). Greater distortion occurred with increasing degrees of catheter shaft angulation, and was more pronounced in images from older catheters. The lumen area measurements in images in which no artefact was identified were accurate to within +/- 10% in 97% of cases, compared to only 81% of cases when an artefact was noted. The quantitative accuracy of an image in which geometric distortion is identified is thus not reliable. The direction of the quantitative error cannot be confidently predicted in any given case, although the mean lumen area tends to increase as the grade of distortion increases.

Rapid diagnosis of chronic myeloid leukaemia by linking PCR to capillary gel electrophoresis.

The move to the use of molecular diagnostics in medicine has gathered momentum in the last few years and new methodologies are being sought to reduce the labour component and hence the cost of these molecular diagnostics. A method is described which links PCR to capillary electrophoresis and this allows both a rapid and quantitative diagnosis. In the example provided, the diagnosis of chronic myeloid leukaemia, the method describes improvements in cost per test, greater sensitivity over traditional methods and an estimate of the level of product. The latter points are important in those disorders for which bone marrow transplantation is used as a curative regime in providing earlier detection of relapse.

The molecular genetics of C1 utilizing microorganisms. An overview.

The availability of recombinant DNA techniques has enabled the successful genetic analysis and manipulation of a range of C1 utilizing microorganisms. It has resulted in the identification of genes of interest on both plasmids and the chromosome; enabled the linkage of chromosomal genes to be determined; established the function and regulatory patterns of genes essential for utilization of C1 compounds and provided information on the evolution of methanogenic bacteria.

Sensitivity of c-erbB positive cells to a ligand toxin and its utility in purging breast cancer cells from peripheral blood stem cell (PBSC) collections.

Autografting following high-dose conditioning is being increasingly offered to breast cancer sufferers, without due regard to the reinfusion of malignant cells. We sought to determine if a breast cancer cell line could be successfully purged from peripheral blood stem cell (PBSC) harvests using a ligand-toxin molecule directed to heregulin-activated erbB receptors. Initial experiments demonstrated no reduction in hemopoietic colony-forming ability in the presence of ligand toxin (2 nM). Breast cancer cell lines which demonstrated differing sensitivities to the ligand toxin were subsequently seeded into stem cell collections and incubated with 2 nM ligand-toxin. One cell line, ZR-75-1, was completely sensitive to the ligand toxin in this mixture; a second, MDB-MA-361, was more profoundly sensitive to the ligand toxin in the presence of the PBSC, whereas a third was unaffected by the toxin. These results suggest purging may indeed be possible in the PBSC of breast cancer patients, but the parameters that define sensitivity are as yet unknown.

Analysis of reproducibility of reference lumen quantitation with intravascular ultrasound in stented coronary arteries.

Intravascular ultrasound is widely used to guide coronary stent implantation. The key quantitative criterion for successful implantation is the demonstration of adequate expansion of the stented lumen relative to that of the adjacent reference vessel segments. In this study we aimed to establish the reproducibility of intravascular ultrasound measurements of the reference segments in lesions undergoing coronary stenting. Measurements of the reference segment lumen dimensions warn made in a blinded fashion by two experienced observers, and reproducibility was assessed by calculating the mean difference and standard deviation of the paired measurements. The unselected intraobserver random variability of the mean reference lumen area measured 0.6 mm2. The interobserver random variability was 0.94 mm2. The intraobserver and interobserver variability of minimum lumen area within the stent was smaller, measuring 0.30 mm2 and 0.52 mm2, respectively. There was 91% intraobserver agreement, and 75% interobserver agreement, in identifying adequate stent expansion as defined by a stent-to-mean reference lumen area ratio of > 0.8. The potentially significant level of variability inherent in selecting and measuring the reference segments, and its impact on clinical decision-making, should be remembered when this method of assessing the acute quantitative outcome of stent implantation is applied.