Maheshwari Aditi, Manstein Nelson, Warner-Levy John, Warner-Levy Alexander, Alfonso Connor M, Doyle Abigail E, Wang-Evers Michael
Department of Dermatology, Harvard Medical School, Massachusetts General Hospital, Cutaneous Biology Research Center, Boston, Massachusetts, USA.
Lasers Surg Med. 2025 Sep;57(7):618-624. doi: 10.1002/lsm.70050. Epub 2025 Jul 27.
Fractional Photothermolysis (FP) relies on precise laser focus to create microscopic treatment zones (MTZs). Focal plane deviations, caused by handpiece pressure and movement, shift the treated tissue out of focus, increasing spot size and reducing lesion depth, compromising treatment efficacy. This study investigates an optimized spacer to mitigate load-induced deviations and improve clinical outcomes.
A difference frequency generation (DFG) laser system (IPG Medical) with 3050/3200 nm wavelength treated ex vivo human abdominoplasty skin, mounted on a load-adjustable platform (0-1000 g, ±0.1 g). Tissue was treated at 5 mJ/pulse with a nominal spot size of 40 µm using spacers ranging from 2 × 2 mm to 8 × 8 mm and an optimized 2 × 2 mm grid spacer. Optical coherence tomography measured skin bulging and focal plane deviations, while histological analysis validated lesion depth and diameter. Knife-edge technique projections were used to assess theoretical beam behavior.
Applied load caused skin bulging, resulting in a linear increase in lesion diameter and a linear decrease in depth. Smaller spacers (2 × 2 mm) reduced focal deviations and maintained MTZ precision within the Rayleigh range. 2 × 2 mm grid spacers further reduced bulging by redistributing the load and ensuring more uniform MTZ formation.
Load-induced focal shifts significantly impact FP efficiency, particularly on nonuniform skin surfaces. An optimized spacer enhanced precision by minimizing bulging, allowing treatments to remain within one Rayleigh length. These findings highlight the clinical importance of spacer selection in achieving consistent FP outcomes, particularly for small-spot laser applications. Clinicians should integrate smaller or grid-patterned spacers to enhance procedural accuracy.
分次光热解（FP）依靠精确的激光聚焦来创建微观治疗区域（MTZs）。由手持件压力和移动引起的焦平面偏差会使治疗组织偏离焦点，增加光斑尺寸并减小损伤深度，从而影响治疗效果。本研究调查了一种优化的间隔物，以减轻负载引起的偏差并改善临床结果。
一台波长为3050/3200 nm的差频产生（DFG）激光系统（IPG Medical公司）对安装在负载可调平台（0 - 1000 g，精度±0.1 g）上的离体人腹壁成形术皮肤进行治疗。使用尺寸从2×2 mm到8×8 mm的间隔物以及优化的2×2 mm网格间隔物，以5 mJ/脉冲的能量、40 µm的标称光斑尺寸对组织进行治疗。光学相干断层扫描测量皮肤隆起和焦平面偏差，而组织学分析验证损伤深度和直径。采用刀口技术投影来评估理论光束行为。
施加的负载导致皮肤隆起，致使损伤直径呈线性增加而深度呈线性减小。较小的间隔物（2×2 mm）减少了焦点偏差，并在瑞利范围内保持MTZ精度。2×2 mm网格间隔物通过重新分配负载并确保更均匀的MTZ形成，进一步减少了隆起。
负载引起的焦点偏移显著影响FP效率，尤其是在皮肤表面不均匀的情况下。优化的间隔物通过最小化隆起提高了精度，使治疗保持在一个瑞利长度范围内。这些发现凸显了间隔物选择在实现一致的FP结果方面的临床重要性，特别是对于小光斑激光应用。临床医生应采用较小的或网格图案的间隔物来提高手术准确性。
