Photoacoustic method monitors spinal muscular atrophy

21 May 2024

University of Erlangen-Nuremberg technique yields more details than MRI, is more comfortable for pediatric patients.

The disease called spinal muscular atrophy (SMA) is a progressive neuromuscular disorder in which certain nerves responsible for sending signals to muscles degenerate, and the muscles themselves waste away.

MRI and ultrasound techniques can be used to diagnose the condition; but the former is not best suited to the examination of young children, and the latter cannot detect specific biomarkers of interest.

A project at University Hospital Erlangen and the University of Erlangen-Nuremberg (FAU) has now applied photoacoustic imaging, also called optoacoustic imaging (OAI), to the task, and believes that it could improve clinical prospects for patients and allow the assessment of gene therapy treatments.

The study is the latest example of photoacoustic methods translating towards clinical use. The technique's ability to image hemoglobin molecules and hence provide valuable information about blood vessels and blood flow shows promise for diverse clinical scenarios, including cancer diagnosis, neural imaging and heart surgery.

As described in the journal Med, the new project's OAI technique combines high optical contrast and deep tissue penetration over several centimeters, according to the FAU project team.

"While two-dimensional OAI has previously been used to assess different inflammatory and degenerative diseases, three-dimensional OAI may further improve visualization and signal quantification," commented the project in its paper.

"In this study, we assessed the imaging capabilities of three-dimensional OAI to resolve muscle degeneration and therapeutic effects in SMA."

Impressive images from optotacoustic data

The three-dimensional capabilities of the technique could be particularly significant for SMA, since it should allow muscle degradation caused by the disease to be quantified; a difficult task with existing diagnostic methods.

In trials on ten pediatric patients, the FAU team observed that two-dimensional OAI was able to indicate the general extent of the disease through a significant reduction of the optoacoustic signal intensity, revealing a reduction in muscle mass and correlating with disease severity.

But 3D volumetric data was potentially more accurate, due to the lesser extent of artifacts and out-of-plane signals. Volumetric data might also improve visualization of specific tissue patterns, giving clinicians a better picture of how treatment programs are affecting the disease.

In a cohort of patients who received disease-modifying therapy prior to the study, the optoacoustic signal intensity was observed to become similar to healthy controls, suggesting that an OAI technique does indeed allow the efficacy of treatments to be studied.

"If muscles are wasting away and becoming replaced with connective tissue, the three-dimensional images show how the disease is progressing and leading to greater quantities of collagen, thereby documenting the wasting of muscle mass," commented the FAU project.

"This provides doctors with a tool that is as quick and easy to use as an ultrasound scan, and delivers impressive images of how muscles and connective tissue come and go."