Measurement of Thermal Effects of Doppler Ultrasound: An In Vitro Study

Thermal analysis and SNR comparison of CMUT and PZT transducers using coded excitation

Coded excitation (CE) has the ability to enhance image quality and penetration depth by improving the signal-to-noise ratio (SNR). Their usefulness has been extensively proven in the literature, however, there are very few publications that have discussed the practicality of using CEs, as they can increase the operating temperature of a transducer beyond the safety limits. In this paper, the potential for capacitive micromachined ultrasonic transducers (CMUTs) to handle CEs is investigated and compared to a geometrically similar Lead Zirconate Titanate (PZT) probe. It is hypothesized that CMUTs are comparatively advantageous for CE and can generate CE signals more effectively while operating within the safety limits of temperature specified by the International Electrotechnical Commission (IEC). Simple chirp signals were used for excitation and the temperature of the transducer assembly was measured under two different test conditions following the IEC standards. The still air test showed that at the pulse repetition frequency of 4 kHz and a signal duration of 8μs, the PZT probe reached the safe limit of 27 °C within 3 min of acquisition, whereas the CMUT probe showed an increase of only 4-5 °C over 30 min of scan time. The phantom experiments showed that for the maximum temperature rise allowed at the object-transducer interface by the IEC, the gain in SNR possible for the CMUT probe was 13-14 dB and the increase in penetration depth was 30 mm, whereas no gain in SNR and penetration depth was achieved for the PZT probe. The peak mechanical index and the derated spatial peak temporal averaged intensity were found to be less than half the FDA limits for both probes in all cases, proving temperature to be the first limiting factor when using CE. Therefore, the CMUT has shown to be thermally more efficient than the PZT probe and a good candidate for CE imaging.

Australian sonographers' perceptions of patient safety in ultrasound imaging: Part 1 - identifying the main safety concerns, a qualitative study

Introduction

Patient safety has been an undervalued component of quality healthcare but is a challenging area of research.Ultrasound is the most common imaging modality in the world. Research on patient safety in ultrasound is generally focused on bioeffects and safe operation of ultrasound equipment. However, other safety issues exist in practice that warrant consideration.This paper forms the first part of a PhD study exploring patient safety in medical diagnostic ultrasound, beyond the notion of bioeffects.The ultimate aim of the study is to inform the final phase of the research study which will consider the next steps in improving the quality and safety of healthcare experienced by patients.

Methods

A qualitative study using semi-structured, one-on-one interviews. A thematic analysis categorised data into codes and generated final themes.

Results

A heterogeneous mix of 31 sonographers, who reflected the profile of the profession in Australia, were interviewed between September 2019 and January 2020. Seven themes emerged from the analysis. These were bioeffects, physical safety, workload, reporting, professionalism, intimate examinations and infection control.

Conclusion

This study presents a comprehensive analysis of sonographers' perceptions of patient safety in ultrasound imaging, not previously available in the literature. Consistent with the literature, patient safety in ultrasound tends to be viewed in technical terms through the potential for bioeffects of tissue damage or physical harm to the patient. However, other patient safety issues have emerged, and while not as well recognised, have the potential to negatively impact on patient safety.

A systematic scoping review to identify the design and assess the performance of devices for antenatal continuous fetal monitoring

BACKGROUND

Antepartum fetal monitoring aims to assess fetal development and wellbeing throughout pregnancy. Current methods utilised in clinical practice are intermittent and only provide a 'snapshot' of fetal wellbeing, thus key signs of fetal demise could be missed. Continuous fetal monitoring (CFM) offers the potential to alleviate these issues by providing an objective and longitudinal overview of fetal status. Various CFM devices exist within literature; this review planned to provide a systematic overview of these devices, and specifically aimed to map the devices' design, performance and factors which affect this, whilst determining any gaps in development.

METHODS

A systematic search was conducted using MEDLINE, EMBASE, CINAHL, EMCARE, BNI, Cochrane Library, Web of Science and Pubmed databases. Following the deletion of duplicates, the articles' titles and abstracts were screened and suitable papers underwent a full-text assessment prior to inclusion in the review by two independent assessors.

RESULTS

The literature searches generated 4,885 hits from which 43 studies were included in the review. Twenty-four different devices were identified utilising four suitable CFM technologies: fetal electrocardiography, fetal phonocardiography, accelerometry and fetal vectorcardiography. The devices adopted various designs and signal processing methods. There was no common means of device performance assessment between different devices, which limited comparison. The device performance of fetal electrocardiography was reduced between 28 to 36 weeks' gestation and during high levels of maternal movement, and increased during night-time rest. Other factors, including maternal body mass index, fetal position, recording location, uterine activity, amniotic fluid index, number of fetuses and smoking status, as well as factors which affected alternative technologies had equivocal effects and require further investigation.

CONCLUSIONS

A variety of CFM devices have been developed, however no specific approach or design appears to be advantageous due to high levels of inter-device and intra-device variability.

Sonographic Evaluation of Fetal Cardiac Anatomy in the Late First Trimester

Objective:

Congenital heart defects (CHDs) are the most common cause of infant death in the United States. Severe, complex cardiac anomalies make up approximately half of the cases and carry significant morbidity and mortality. The purpose of this literature review was to define a CHD screening protocol to be used in the first trimester.

Methods:

Literature was pulled that discussed the impact of color Doppler and spatiotemportal image correlation on image quality, explored the benefits and limitations of early screening, and analyzed the risk of bioeffects to the developing fetus.

Results:

A simplified cardiac screening protocol has been shown to be a feasible addition to the first trimester nuchal translucency scan.

Conclusion:

Color Doppler and three-dimensional sonography can be utilized during the first trimester to evaluate the fetal heart for major anomalies between 11 weeks and 13 weeks 6 days. Recommendations for future research and guidance from accrediting bodies are provided.

Color Doppler ultrasound of spiral artery blood flow in mid first trimester (4-8 weeks) in cases of threatened abortion and in normal pregnancies

Introduction

The aim of the study was to evaluate and compare the spiral artery flow in mid first trimester (4–8 weeks) in cases of threatened abortion and in normal pregnancies.

Material and methods

Spiral artery was sonographically evaluated in 50 patients comprising two groups of 25 women each. The first group included patients presenting with threatened miscarriage (vaginal bleeding/spotting with or without abdominal pain). The second group comprised of females who had no complications, but had no desire to continue the pregnancy. Spiral artery flow velocity measurements were performed using Color Doppler (Pulsatility Indices, Resistive Indices and Systolic/diastolic values) in mid first trimester (between 4–8 weeks of gestation), each measurement was performed twice. Statistical analysis was performed using Statistical package for social sciences software. Values were rounded off to two digits after decimal point.

Results

Significant differences were noted in the spiral artery Doppler values in the two groups. In particular, the Resistive Indices was higher in cases of women with threatened miscarriage. The difference in Pulsatility Indices was also statistically significant between the two groups.

Conclusion

Doppler values of spiral artery may be used as a useful parameter in assessing the prognosis in cases presenting with threatened miscarriage.

Blood Pressure Profiles in Infants With Hypoxic Ischemic Encephalopathy (HIE), Response to Dopamine, and Association With Brain Injury

Objective: To describe mean arterial blood pressure (MABP), responsiveness to dopamine, and relationship to brain injury in infants with moderate/severe hypoxic-ischemic encephalopathy (HIE) undergoing therapeutic hypothermia (TH). We hypothesized that, when utilized, dopamine would rapidly and effectively increase MABP in treated patients. Methods: Continuous arterial blood pressure measurements were prospectively recorded from infants with moderate/severe HIE undergoing TH in a multi-institutional cohort from 2010 to 2018. Treatment with dopamine was at the discretion of the medical team for hypotension/hypoperfusion. MABP values of treated infants were compared to those obtained at an equivalent time period in control infants receiving TH but not dopamine (24 h after birth). MRI was obtained per unit protocols and included T1/T2/DWI sequences. Injury was classified as no injury/mild injury or moderate/severe injury using a standardized scoring system. Seizures were confirmed with conventional EEG. Results: Eighteen infants were treated with dopamine and were similar to untreated controls (n = 36) with the exception of lower cord gas pH (6.92 ± 0.2 vs. 7.07 ± 0.2, p < 0.05). Dopamine was initiated at a mean of 24 h after birth. MABP was significantly lower in the dopamine group at the start of therapy (39.9 ± 2.0 vs. 49.1 ± 1.3, p < 0.01) and 1 h later (44.3 ± 2.0 vs. 49.8 ± 1.1, p < 0.05). However, after 9 h of treatment, dopamine increased the MABP by an average of 9 mmHg and MABP values were similar to untreated controls for the remainder of the observation period. There were no significant differences in rates of seizures, brain injury, or death. Conclusion: Neonates with moderate/severe HIE treated with dopamine during TH had MABP significantly lower than controls. The majority of infants responded to dopamine monotherapy following adequate volume resuscitation. An association between requirement for dopamine and severity of brain injury was not detected.