Focused Ultrasound: Definition, Applications, and Impact

Non-communicable diseases are slowly getting too much for the world to bear. Disorders like cancer and cardiovascular diseases have become a household phenomenon. We seem to have accepted it as normal. Millions are dying every year and millions more are getting affected by the complexity of these NCDs. Healthcare systems aren’t really equipped to deal with these problems. Focused ultrasound, however, has shown hope. 

Non-communicable diseases: A grave situation worldwide 

Everybody took notice when global casualties started rising due to Covid-19. But no one is talking about the silent pandemic of non-communicable diseases. It is far more devastating than all the Covid variants combined and it’s going on a rampage albeit silently. 

Here are some facts on non-communicable diseases: 

  • 74% of all deaths in the world happen due to non-communicable diseases.
  • 41 million people are killed every year.
  • 17 million people die every year before the age of 70 because of NCDs 

The above figures are released by the World Health Organisation. Can you imagine how alarming the situation is when 3/4th of the entire deaths in the world are caused by NCDs? 

The scourge of NCDs points to one important thing. We need better diagnostic methods to treat these disorders. Investment in non-invasive techniques like focused ultrasound is particularly crucial. Improvements in ultrasound transducer development would go a long way in tackling the NCD problem.

But let’s understand the problem of NCDs first.

What are NCDs? 

These are a group of disorders that develop inside the body over a long period. NCDs cover a wide group of diseases that happen either through infections or changes in cellular composition. They don’t spread by contact like communicable diseases. They are caused by genetic, lifestyle, or environmental stressors.

The major types of NCDs are: 

  • Cardiovascular diseases like heart attack and stroke – about 18 million deaths per year
  • Cancer – 9.3 million deaths per year
  • Chronic respiratory disease – 4.1 million deaths per year
  • Diabetes and kidney failure – 2 million deaths per year

Why are there so many NCD deaths worldwide? 

A major reason for rising NCD casualties is inefficient healthcare infrastructure. Diagnostic equipment and treatment options aren’t evolving at the same pace as these disorders. Low- and middle-income countries also have to deal with apathy.

It’s sad that we haven’t progressed far even after so much research on NCDs. We haven’t been able to prevent deaths that were preventable. Granted, a lot of NCDs happen due to lifestyle issues and neglect of physical and mental health. It still doesn’t explain why even advanced healthcare systems are falling short. 

In this context, focused ultrasound has emerged as a ray of hope. Let’s discuss more about this technology here. 

About focused ultrasound

Focused ultrasound is a non-invasive therapeutic technology that uses the power of high-intensity ultrasound waves. The energy created by these high-intensity waves, when channeled properly can treat the target tissue effectively. 

It’s a novel therapeutic technique that has given tremendous results in various trials. It’s hard to believe that a noninvasive method can be so effective against deep tissue maladies. 

Focused ultrasound goes through two main stages: 

  • Ultrasound imaging: Using a powerful imaging tool helps to identify the tissue to be modified or destroyed. This is necessary to control the effectiveness of the treatment in real-time.
  • High-intensity focused ultrasound: HIFU beams are released on the target tissue with the utmost precision. The beams are passed after the target tissue is identified.

Principles of focused ultrasound

Focused ultrasound works on the same principle as burning a piece of paper with a magnifying glass. When you hold the latter above the paper and let the sun’s beams focus on a single point, it creates a burning hole soon. The ultrasound beam does a similar job. The only difference is that the beam consists of ultrasound waves and the target is a tissue. Also, the tissue-burning process is called ablation.

The ultrasound waves are passed by a transducer. The better the transducer, the more impactful the procedure is. Ultrasound transducer development is thus another critical aspect of focused ultrasound.

We touched upon the precision and accuracy of this therapeutic method before. But how precise? Depending on the arbitrary waveform generator and the transducer quality, a tissue as small as 1×1.5 mm can be ablated. 

Trends in ultrasound transducer development

As the principle of focused ultrasound suggests, you need to focus high energy ultrasonic beams on the shark-defined tissue region. This will ensure rapid heating and achieve the desired cytotoxicity with thermal ablation. Only high-quality transducers that use the right material can achieve this.

Let’s see how transducers evolved over the years to make such thermal ablation possible.

  1. Quartz material

However, high-intensity beams don’t just magically reach the selected spot. It needs good transducers to guide the beams accurately. Earlier, quartz was the material of choice in transducers but their effectiveness is limited. A major reason why focused ultrasound therapy wasn’t sophisticated enough in the early stages was due to the limitations of the quartz material.

  1. Piezoelectric materials

Things changed when piezoelectric transducers were developed. These transducers use novel materials like – 

  • Piezo ceramics – PZT (Lead zirconium titanate) 
  • Other Piezo composite materials like PMN-PT 

Lead Magnesium Niobate-Lead Titanate or PMN-PT is a highly advanced piezoelectric material. It has proved to be far more effective than other composite materials.

The piezoelectric materials are being used in phase array transducers to steer the ultrasound beam more accurately. Ultrasound transducer development peaked with the emergence of phase array transducers.

Single-element bowl transducers vs piezoelectric composite material phased array transducers

The main problem with a single-element bowl transducer is that it isn’t flexible with its focal length. While it does its job of wave transmission well, it can’t be relied upon when there are issues of accessibility. It simply won’t work when you are delivering high-power ultrasound beams to brain tissues and thermal ablation could go terribly wrong.

Phased array transducers with piezoelectric composite materials are perfectly suited when you want flexibility in focal lengths. Such transducers enhance your inspection coverage and also the speed of inspection. They give us exceptional directional control of the ultrasonic beams, that makes it possible to follow a predetermined trajectory.

Effectiveness of phased array transducers in the delivery of ultrasound beam

Phased array transducers are designed such that the ultrasound beam can be focused in a localized area. What is called the localized tissue area is generally the tumor that’s to be targeted. It works best in tumors of 3-4 cm in diameter; however, recent developments allow you to target even a 1 cm tumor! 

A focused ultrasound beam is made to pass through the skin to cause the coagulative thermal necrosis of the tumor. The cell temperature rises as high as 60℃ which is absorbed by the tumor cells. The latter can’t survive the focused heat and undergoes necrosis or cell death. 

Another aspect of focused ultrasound is the formation of mechanical stress on the tumor. High-intensity ultrasound beams cause cavity formation in the cell. This leads to the development of high shear stress in the cell due to an increase in temperature and pressure. The cell wall collapses under this stress and cell death begins.

Such immense precision means focused ultrasound therapy can eliminate the need for surgical incisions. At least in a majority of tumor cases.  The non-invasive treatment has the potential to be a safe and cost-effective therapeutic approach in the future. 

Even better is its ability to identify and destroy potentially damaging tissues in the initial stages itself. This can prevent malignancy.

Applications of focused ultrasound

A vital application of focused ultrasound is in the field of cancer treatment. Cancer cases are rising exponentially all around the world, especially in poor countries. The current treatment methods i.e. surgery and chemotherapy, are costly and physically draining. The non-invasive approach of focused ultrasound makes it more effective and less physically straining. The area of coverage is also diverse.

  1. Brain 

Glioblastoma or brain tumor can be treated with the help of focused ultrasound. It’s a useful way to open the blood-brain barrier and deliver drugs or to cause thermal ablation of tumorous cells.

  1. Breast

This non-invasive treatment has shown great promise in treating breast tumors. It monitors and ablates breast tumors in real-time.

  1. Bone

HIFU treatment sessions have been able to treat both benign bone tumors and metastasized tumors. It has shown good results in regulating the spread of bone lesions.

  1. Liver 

The focused ultrasound treatment has shown good results when it comes to treating liver tumors. Even a single HIFU session can result in great hepatic recovery.

  1. Kidney

The development of renal masses is quite painful to the body. HIFU treatment sessions have proved effective in eliminating undesirable renal masses.

  1. Pancreas

Pancreatic tumors often go undetected and by the time it’s detected, surgery is the last remaining option. HIFU helps in the non-surgical treatment of pancreatic tumors with its precision beams leading to quick tumor ablation.

Key Takeaway

Focused ultrasound has far-reaching implications in the treatment of non-communicable diseases. This non-invasive therapy can be a great leveler as it’s accurate and cost-effective. Advances in ultrasound transducer development have only complemented its sharp accuracy.

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