Treatment of twin-reversed arterial perfusion sequence using high-intensity focused ultrasound

We describe our experience of high-intensity focused ultrasound (HIFU) for fetal therapy in twin-reversed arterial perfusion (TRAP) sequence. Six pregnant women underwent HIFU therapy, five before 16 weeks and one at 26 weeks. Two types of HIFU system were used: the first-generation system, which comprised a biaxial transducer and continuous exposure pattern, and the second-generation system, which comprised a coaxial transducer and sequential exposure pattern. The first-generation apparatus was used in four cases and the second-generation apparatus was used in two. In three cases, occlusion of the blood vessels mediating flow to the acardiac twin was achieved by HIFU. Two cases experienced intrauterine fetal death despite vessel occlusion. The total survival rate of pump fetuses 2 years after HIFU was 67% and the efficiency rate (the proportion of cases with occlusion or reduced blood flow on ultrasound after HIFU) was 83%. After more than 2 years of follow-up, the surviving infants had no severe clinical complications and no postnatal developmental problems. There was no significant difference in survival rate compared with TRAP cases managed expectantly. Given that complete occlusion of the blood vessels was not achieved in half of the cases, we could not show that HIFU therapy is superior to other treatments. However, HIFU can reduce the cardiac load of the pump fetus and, as it does not require uterine puncture for fetal therapy, there were no fatal complications, such as bleeding, rupture of membranes or infection. Thus, HIFU therapy may represent a less-invasive treatment for TRAP sequence in early pregnancy. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Pharmacokinetic study of a gallium-porphyrin photo- and sono-sensitizer, ATX-70, in tumor-bearing mice

The tissue distribution of a gallium-porphyrin photo- and sono-sensitizer, 7,12-bis(1-decyloxyethyl)-Ga(III)-3,8,13,17-tetramethylporphyrin-2,18-dipropionyldiaspartic acid, ATX-70, was pharmacokinetically examined in tumor-bearing mice. The drug was administered intravenously to CDF(1) mice implanted with Colon 26 carcinoma. Blood and tissue samples were collected for up to 72 h after administration. The drug concentration was determined by high-performance liquid chromatography (HPLC) with fluorescence detection. ATX-70 was found to accumulate in tumors at a relatively high concentration that peaked between 2 h and 6 h after administration. However, modest concentrations of ATX-70 also remained in healthy tissues for up to 6 h. We examined the distribution of ATX-70 in the tumor in comparison with other tissues from the viewpoint of minimizing possible side effects of laser or ultrasound exposure while maintaining the treatment effect. About 24 h after administration, the tumor / plasma concentration ratio peaked, and relatively high tumor / skin and tumor / muscle concentration ratios were seen.

Insonation of fixed porcine kidney by a prototype sector-vortex-phased array applicator

The sector-vortex applicator, an ultrasound phased array with a geometric focus having multiple sectors and tracks, can directly synthesize, without scanning, diffuse focal patterns useful for hyperthermia. A perfused tissue phantom, consisting of an alcohol-fixed porcine kidney with thermocouples placed in the cortex, is insonated by a prototype sector-vortex applicator with 16 sectors and two tracks at an ultrasound frequency of 750 kHz. Steady-state temperature distributions are measured for a wide range of perfusion rates. Results demonstrate that the radius of the heated region can be controlled effectively by choosing the focal mode of the applicator as it is predicted by theoretical analysis.

Analysis of temperature responses to diffused ultrasound focal fields produced by a sector-vortex phased array

The sector-vortex applicator, a disc-shaped ultrasound phased array with a geometric focus having multiple sectors and tracks, can directly synthesize, without scanning, diffuse focal patterns useful for hyperthermia. Temperature distribution patterns resulting from these acoustic fields have been simulated by solving a steady-state bioheat equation numerically for a wide range of blood perfusion rates. These results suggest that the sector-vortex array will be particularly suitable for heating non-superficial small tumours. The temperature distribution pattern changes due to variations in blood perfusion are interpreted based on spatial frequency domain Fourier analysis of temperature responses to different power deposition patterns. The system behaves like a low-pass spatial frequency filter.

A cylindrical-section ultrasound phased-array applicator for hyperthermia cancer therapy

A phased-array applicator geometry for deep localized hyperthermia is presented. The array consists of rectangular transducer elements forming a section of a cylinder that conforms to the body portals in the abdominal and pelvic regions. Focusing and scanning properties of the cylindrical-section array are investigated in homogeneous lossy media using appropriate computer simulations. The characteristic focus of this array is shown to be spatially limited in both transverse and longitudinal directions with intensity gain values suitable for deep hyperthermia applications. The ability of the cylindrical-section phased array to generate multiple foci using the field conjugation method is examined. The effect of the grating lobes on the power deposition pattern of the scanned field is shown to be minimal. Steady-state temperature distributions are simulated using a three-dimensional thermal model of the normal tissue layers surrounding a tumor of typical volume. The advantages and the limitations of this array configuration are discussed.