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PD is a new CD imaging imaging mode that might be superior to CD in some cases.

Technological developments and greater rigor in the quantitative measurement of biological features in medical images have given rise to an increased interest in using quantitative imaging biomarkers (QIBs) to measure changes in these features. Critical to the performance of a QIB in preclinical or clinical settings are three primary metrology areas of interest: measurement linearity and bias, repeatability, and the ability to consistently reproduce equivalent results when conditions change, as would be expected in any clinical trial. Unfortunately, performance studies to date differ greatly in designs, analysis method and metrics used to assess a QIB for clinical use. It is therefore, difficult or not possible to integrate results from different studies or to use reported results to design studies. The Radiological Society of North America (RSNA) and the Quantitative Imaging Biomarker Alliance (QIBA) with technical, radiological and statistical experts developed a set of technical performance analysis methods, metrics and study designs that provide terminology, metrics and methods consistent with widely accepted metrological standards. This document provides a consistent framework for the conduct and evaluation of QIB performance studies so that results from multiple studies can be compared, contrasted or combined.

A prospective study of the Doppler color flow features of 55 proved breast cancers was performed. On a three-level scale of low to marked vascularity, visual assessment of the color flow images classified 82% of the cancers as moderately or markedly vascular (minimal: 14%, moderate: 29%, marked: 53%). Four percent of the cancers had no detectable flow. In 29 women, a volume of tissue comparable to the cancer was scanned in the contralateral normal breast. Sixty-nine percent of the normal breasts had moderate or marked vascularity (minimal: 28%, moderate: 41%, marked: 28%), and 3% were avascular. There was poor distinction between normal tissues and cancer which suggests that more sensitive Doppler methods than were employed in this study may be needed in order to detect the small vessel flow reported to be rather specific for malignancy. The high, 82%, detection rate of tumor vessels in this study suggests the potential use of color flow Doppler for directing more specific but lengthy Doppler procedures.

The vaporization of a superheated droplet emulsion into gas bubbles using ultrasound – termed acoustic droplet vaporization (ADV) – has potential therapeutic applications in embolotherapy and drug delivery. The optimization of ADV for therapeutic applications can be enhanced by understanding the physical mechanisms underlying ADV, which are currently not clearly elucidated. Acoustic cavitation is one possible mechanism. This paper investigates the relationship between the ADV and inertial cavitation (IC) thresholds (measured as peak rarefactional pressures) by studying parameters that are known to influence the IC threshold. These parameters include bulk fluid properties such as gas saturation, temperature, viscosity, and surface tension; droplet parameters such as degree of superheat, surfactant type, and size; and acoustic properties such as pulse repetition frequency and pulse width. In all cases the ADV threshold occurred at a lower rarefactional pressure than the IC threshold indicating that the phase-transition occurs before IC events. The viscosity and temperature of the bulk fluid are shown to influence both thresholds directly and inversely, respectively. An inverse trend is observed between threshold and diameter for droplets in the 1 to 2.5 μ range. Based on a choice of experimental parameters, it is possible to achieve ADV with or without IC.

This paper examines the vaporization of individual dodecafluoropentane droplets by the application of single ultrasonic tone bursts. High speed video microscopy was used to monitor droplets in a flow tube, while a focused, single element transducer operating at 3, 4, or 10 MHz was aimed at the intersection of the acoustical and optical beams. A highly dilute droplet emulsion was injected, and individual droplets were positioned in the two foci. Phase transitions of droplets were produced by rarefactional pressures as low as 4 MPa at 3 MHz using single, 3.25 micros tone bursts. During acoustic irradiation, droplets showed dipole-type oscillations along the acoustic axis (average amplitude 1.3 microm, independent of droplet diameter which ranged from 5 to 27 microm). The onset of vaporization was monitored as either spot-like, within the droplet, or homogeneous, throughout the droplet's imaged cross section. Spot-like centers of nucleation were observed solely along the axis lying parallel to the direction of oscillation and centered on the droplet. Smaller droplets required more acoustic intensity for vaporization than larger droplets, which is consistent with other experiments on emulsions.

The power Doppler US technique has the potential to more accurately estimate alterations in blood flow and has the advantage of being a continuous parameter that can be depth normalized.

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