Recent advances in imaging and evaluation of blood flow using ultrasound

Indocyanine green fluorescence/thermography evaluation of intercostal muscle flap vascularization

Background

During anatomical lung resection in high‐risk patients, the bronchial stump is covered with tissue flaps (e.g. pericardial fat tissue and intercostal muscle) to prevent bronchopleural fistula development. This is vital for reliable reinforcement of the bronchial stump. We evaluated the blood supply of the flap using indocyanine green fluorescence (ICG‐FL) and thermography intraoperatively in 27 patients at high risk for developing a bronchopleural fistula.

Methods

Before reinforcing the stump with a flap, the fluorescence agent was intravenously injected and the blood supply was evaluated. The surface temperature of the flap was measured with thermography. The two modalities were then compared.

Results

ICG‐FL intensity and surface temperature on the distal compared to the proximal side of the flap decreased by 32.6 ± 29.4% (P < 0.0001) and 3.5 ± 2.0°C (P < 0.0001), respectively. In patients with a higher ICG‐FL intensity value at the tip than the median, the surface temperature at the tip decreased by 2.7 ± 1.7°C compared to the proximal side. In patients with a lower ICG‐FL value at the tip, the surface temperature decreased by 4.6 ± 1.7°C (P = 0.0574). The bronchial stump reinforced the part of the flap with adequate blood supply; none of the patients developed a bronchopleural fistula.

Conclusions

ICG‐FL confirmed variation in the blood supply of the intercostal muscle flap, even if prepared using the same surgical procedure. Thermography analysis tends to correlate with the fluorescence method, but may be influenced by the state of flap preservation during surgery.

Color Flow Imaging

The latest change to occur in diagnostic ultrasound is color flow imaging. This technology presents an image with tissue in gray scale and blood flow in color. Image formation can be asynchronous or synchronous, representing different approaches to data gathering, and consequently different internal signal processing. This article focuses on how these technologies deal with problems in imaging and meeting clinical needs, and establishes the basic parameters needed for clinical vascular imaging.

Ultrasound Transducers

Diagnostic medical ultrasound transducers have evolved through the years and have contributed significantly to improved patient care. This article discusses the history and types of transducers and the elements that have changed over time. There has been a sharp transition from natural to human-made elements and from one to many in a single transducer. Ergonomics also now plays a role in transducer design and will continue to do so; the grip, weight, and size of transducers are in the forefront of design considerations. The evolution of transducers has changed not only how well we visualize anatomy and what anatomy we see but also how the patient’s care is managed. Different, new, and emerging technologies certainly will continue to be identified within the sonography community.

Ultrasound in medical education: listening to the echoes of the past to shape a vision for the future

PURPOSE

Ultrasound in medical education has seen a tremendous growth over the last 10-20 years but ultrasound technology has been around for hundreds of years and sound has an even longer scientific history. The development of using sound and ultrasound to understand our body and our surroundings has been a rich part of human history. From the development of materials to produce piezoelectric conductors, ultrasound has been used and improved in many industries and medical specialties.

METHODS

As diagnostic medical ultrasound has improved its resolution and become more portable, various specialties from radiology, cardiology, obstetrics and more recently emergency, critical care and proceduralists have found the added benefits of using ultrasound to safely help patients. The past advancements in technology have established the scaffold for the possibilities of diagnostic ultrasound's use in the present and future.

RESULTS

A few medical educators have integrated ultrasound into medical school while a wealth of content exists online for learning ultrasound. Twenty-first century learners prefer blended learning where material can be reviewed online and personalize the education on their own time frame. This material combined with hands-on experience and mentorship can be used to develop learners' aptitude in ultrasound.

CONCLUSIONS

As educators embrace this ultrasound technology and integrate it throughout the medical education journey, collaboration across specialties will synthesize a clear path forward when needs and resources are paired with vision and a strategic plan.

A modified technique of ultrasonic triplex scanning of the lower extremity arteries

This study was undertaken to evaluate the utility of a modified technique of triplex scanning of the lower extremity arteries in 20 subjects without any clinical signs of arterial disease. The distal aorta and iliac arteries were examined with the subject in supine position and lying slightly on the opposite side. By moderate compression of the probe towards the psoas muscle and directing it over the iliac arteries with slight medial retraction of the abdomen, satisfactory visualization of the common and external arteries with 7.5 MHz high resolution imaging and a 5.6 MHz doppler probe were obtained in 56 of 80 segments (70%). In obese individuals it was necessary to use 5 MHz probe for satisfactory scanning of the aortic bifurcation and common iliac arteries. The distal superficial femoral, popliteal and tibioperoneal trunk segments were examined with the patient prone and the knee slightly flexed. Peak systolic, early diastolic reverse and late diastolic forward flow velocities were studied together with measurement of the arterial diemeters, which demonstrated wide variations. This study suggests that satisfactory scanning of the iliac and femoropopliteal arteries with the described technique can be achieved in the majority of subjects with a superficial high resolution probe. The combination of 7.5 MHz two-dimensional imaging with a 5.6 MHz pulsed wave Doppler probe offers optimal information of these arteries in nonobese individuals.

Duplex examination

BACKGROUND

Accurate venous diagnosis remains a challenge for the phlebologist and vascular laboratory. In recent years duplex ultrasound has become the preferred method of diagnosis for deep venous thrombosis and deep and superficial venous insufficiency.

OBJECTIVE

To describe the physical principles, typical protocol, and indications for venous duplex examination.

CONCLUSION

Duplex examination offers a precise, noninvasive technique to make anatomic and functional venous diagnoses.

Detection of superior mesenteric and coeliac artery stenosis with colour flow Duplex imaging

Measurements of blood velocity in the coeliac axis (CA) and the superior mesenteric artery (SMA) before and after a standard meal in normal people have been studied by several authors. However, information about the ability to detect stenotic lesions is lacking. The aim of our study was to determine the accuracy of Duplex scanning in detecting angiographically proven lesions. Twenty normal volunteers (13 males and seven females) and 24 patients (19 males and five females) with visceral artery stenosis on angiography were examined in the supine position (angle of insonation 60.5) with colour flow Duplex imaging (CFDI) (3.5 MHz probe), in the fasting state and after a standard meal at 15, 40, 60 and 90 min. Peak systolic velocity (PSV) and end diastolic velocity (EDV) were determined in both CA and SMA. The PSV was the best indicator of stenosis. After the meal, there was an increase in both PSV and EDV but neither of the postprandial measurements improved the accuracy of the test. The results indicate that CFDI can detect the presence of significant stenosis (> 50% in the CA and SMA with a sensitivity and specificity of > 80%.

The imaging quality of angiodynography in the ilio-femoral tract

The imaging quality of angiodynography (Quantum; Philips) in the ilio-femoral tract was compared with uniplanar angiography. One hundred ilio-femoral tracts were investigated with both translumbar conventional angiography and angiodynography. The ilio-femoral tract was divided into five parts; proximal and distal common iliac, proximal and distal external iliac and common femoral. Stenosis was scored from 0-24, 25-49, 50-74, 75-99 and 100% and the lengths of those of 25% or more were measured in centimeters. Because the thickness of the subcutaneous fat layer decreases the depth range (normally 11.5 cm) of the 5.0 MHz transducer it was also measured in centimetres. The results showed that a significantly larger number of vessels were not seen (especially the common iliac) with an increasing thickness of the subcutaneous fat. The results based on the real-time imaging quality alone of angiodynography showed a reasonable accuracy of 83.9% when detecting stenoses graded from 0-24, 25-49, 50-74, 75-99 up to 100%. The clinically more important discrimination between a haemodynamically important stenosis of more than 50% showed a sensitivity of 88% and specificity of 98% on visual information alone. By integrating the peak velocity measurements to the results, this sensitivity rose to 95% and the specificity became 99%. The correlation in length was within a range of 1 cm in 94% and within 1-2 cm in 6% of the stenoses. In conclusion, angiodynography is a reliable technique for investigating the ilio-femoral tract.

Use of color-flow imaging technique in carotid artery disease

Color-flow imaging of the cervical vasculature has several distinct advantages compared with conventional duplex scanning: it facilitates identification of the carotid artery, its bifurcation, branches, and other cervical vessels, especially the vertebral arteries; decreases the time required for longitudinal surveys; aids in the recognition of kinks, coils, and occluded vessels; evaluates flow simultaneously in large areas and multiple vessels; and focuses attention on sites of flow disturbance. Although many problems remain, color-flow imaging represents a powerful new tool for the diagnosis and physiologic assessment of extracranial cerebrovascular disease.