Long Duration Ultrasound: Recent Advancements and Clinical Applications

Long-duration low-intensity ultrasound (LDUS) delivers acoustic waves producing localized mechanical and thermal stimuli that modulate cellular and extracellular processes. These stimuli activate mechano transduction pathways, alter extracellular matrix structure, and enhance vascular and metabolic activity, enabling LDUS to serve as a non-invasive therapeutic modality across various clinical domains), particularly through the FDA-approved Sustained Acoustic Medicine (SAM) device, deliver continuous ultrasound at 3 MHz and 132 mW/cm² for long duration. Clinical studies have demonstrated that SAM significantly increases local muscle temperature (up to 14.7°C), intramuscular blood flow (up to 19.2-fold), and targeted drug delivery, resulting in improved pain scores and quality of life in patients with chronic musculoskeletal pain and osteoarthritis. LDUS has also shown efficacy in reducing upper trapezius myofascial pain, chronic lower back pain, and knee osteoarthritis symptoms, with measurable improvements in functional indices, reduced reliance on analgesics, and improved patient-reported outcomes. Commercially available low-intensity ultrasound (LIUS) devices have shown encouraging results in healing bone fracture and soft tissue injuries. Emerging evidence reports demonstrate LIUS enhancing cerebral perfusion, reducing vascular stiffness, and improving targeted drug delivery. Novel approaches using microbubbles, focused ultrasound, and thermosensitive carriers have enabled localized treatment of glioblastoma, liver metastases, and spinal cord injury with reduced systemic toxicity. Standardization of LIUS parameters-including frequency, intensity, and duration-remains essential to optimize efficacy across indications. Optimizing ultrasound modalities (mechanical vs. thermal) based on disease pathophysiology and combining them with adjunctive technologies (e.g., nanoparticles, implantable) can have significantly beneficial effects.