The aim of this explorative pilot study is to present muscle perfusion of the lower extremity in patients with PAD using the Multispectral Optoacoustic Tomography (MSOT) method to build a 3D reconstruction of the calf muscle. This study aims to show the feasibility of 3D reconstruction of this non-invasive method. Advantages in diagnostics for patients with PAD and three-dimensional tomography representation of the perfusion situation based on muscle oxygenation will be evaluated.

Functional imaging diagnostics is becoming increasingly important due to the steadily growing knowledge of physiological processes in many diseases. Also in peripheral arterial occlusive disease (PAD), new insights into the pathomechanism of the disease are continuously being gained. This also increases the need for new non-invasive imaging methods that are able to visualize the functional level of the disease progression and thus make it possible to diagnose it at an early stage.

Recent studies indicate that it may be feasible to use multispectral optoacoustic tomography (MSOT) to visualize hemodynamics as well as the fibrotic muscle remodeling process in PAD. For a better understanding of the distribution pattern , the exploration of a 3D technique is a next necessary step in imaging. This may show a possible existing heterogeneity of these molecules.

Holzwarth et al. were already able to gain knowledge about the 3D reconstruction from 2D photoacoustic image slices using an optical pattern and the method's feasibility using phantoms as well as in-vivo measurements of the forearm in healthy volunteers.

The aim of this exploratory pilot project is to bring these previous findings together and to image muscle perfusion of the lower extremity in three dimensions using the MSOT method and to verify its feasibility. The advantage of 3D imaging is, beyond the anatomical topography of the muscle, to map a three-dimensional representation of the perfusion situation based on muscle oxygenation.

For this purpose, six patients of different symptomatic PAD stages and a healthy control of two volunteers will be included and examined by means of longitudinal MSOT scans in the area of the gastrocnemius muscle. To evaluate the current stage of the disease or to exclude relevant PAD in the healthy control population, non-invasive examination measures commonly used in routine diagnostics of PAD will be applied. In addition to the relevant risk factors/adjacent diseases and the current medication intake, these include the recording of the ankle-brachial index (ABI), color-coded duplex sonographic vascular imaging (CCDS) and a treadmill examination.

Inclusion Criteria:

• Patients with manifest PAD stages II-IV according to Fontaine or healthy volunteers
• Adult (>18 years) persons who are able to give their consent

Exclusion Criteria:

• Patients with PAD stage I according to Fontaine
• Healthy volunteers with pre-existing diabetes mellitus, chronic renal failure, or abnormal ABI
• Underage persons
• Missing consent form
• Exclusion due to safety concerns of the study physician (patient with a physical, mental or psychiatric illness which, in the opinion of the study physician, would compromise the safety of the patient or the quality of the data and thus make the patient an unsuitable candidate for the study)

Patients with PAD IIa/IIb/III/IV according to Fontaine who come in for a routine presentation of the the vascular surgery consultation hours.

Healthy volunteers with

• no PAD previously known
• no diabetes mellitus previously known
• no chronic renal insufficiency previously known
• no symptoms in the sense of a Claudicatio intermittens
• ABI with normal value who are recruited by clinic notices.