Imaging method for displaying the tissue perfusion

In tissue perfusion or microcirculation diagnostics, imaging analysis is commonly realized with the Laser Speckle method. However, that procedure can only record micro movements in the tissue. The image quality strongly depends on the optical characteristics of the upper skin layers.
The important parameter tissue oxygenation can only be acquired indirectly via Laser Speckle. In contrast, HSI-technology enables a direct recording of tissue oxygenation.

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PAD – peripheral arterial disease
PAD describes the narrowing of the arteries in extremities, which leads to insufficiently oxygenated tissue. This is most commonly caused by arteriosclerosis. PAD is usually accompanied by an increased risk for cardio-vascular diseases that can cause heart attacks and strokes.
By the targeted use of our TI-CAM system, signs of PAD can be detected earlies and countermeasures will be more efficient.

“These results suggest the ability of hyperspectral imaging to detect the presence of PAD. Hyperspectral
measurements can also evaluate different severities of PAD.

[J Vasc Surg 2011;54:1679-88.]

“Conclusion: We found sufficient evidence to use NIRS in clinical setting for assessment of chronic compartment syndrome of lower extremities, and as surveillance tool for detection of free flap failure. So far, clinical relevance of routine use of NIRS in other vascular applications is less clear. Cut-off values to discriminate are not yet unanimous and better validation has to be awaited for.”
[Boezeman, Reinout PE, et al. “Systematic review of clinical applications of monitoring muscle tissue oxygenation with near-infrared spectroscopy in vascular disease.” Microvascular research 104 (2016): 11-22.]

As part of an internal validation study for the TI-CAM an occlusion test was performed.
For the measurements, the perfusion of the left hand was regulated via a blood pressure cuff attached to the left arm. Additionally, in order to validate the measured data, a sport monitoring sensor (MOXY) was attached to the left hand. The right hand was left untouched for the test procedure. During the testing sequence, which lasted 28 mins in total, both hands were recorded simultaneously every 30 secs and the data was analyzed. The test consisted of the following phases:
• Normal state I (4 mins)
• Venous occlusion (6 mins)
• Normal state II (6 mins)
• Arterial occlusion (6 mins)
• Reperfusion (6 mins)

In the following, the results are presented.

Overview of the results of the testing sequence: Right hand is continuously in a normal state (left hand in the image), left hand with the MOXY monitor during the course of the test. The phase normal state II is not depicted. The lowest row shows the respective averaged values, acquired from the middle of the palm, as a spectrum. The upper graph represents the left, the lower graph the right palm.

Overview of the results of the testing sequence: Right hand is continuously in a normal state (left hand in the image), left hand with the MOXY monitor during the course of the test. The phase normal state II is not depicted. The lowest row shows the respective averaged values, acquired from the middle of the palm, as a spectrum. The upper graph represents the left, the lower graph the right palm.

Normal „healthy“ perfusion (normal state I)
Duration: 4 mins
Method: –
Characteristics: two sided, even oxygenation levels (~60-70 %) and NIR perfusion, almost identical distribution of hemoglobin

Venous occlusion
Duration: 6 mins
Method: occlusion of the left arm via blood pressure cuff at 80 mmHg
Characteristics: moderate decrease of tissue oxygenation (~35-45 %) and NIR perfusion as well as increase in THI levels

Normal state II
Duration: 6 mins
Method: –
Characteristics: even oxygenation and NIR perfusion, decrease of THI levels

Arterial occlusion
Duration: 6 mins
Method: occlusion of left arm via pressure cuff at 250 mmHg
Characteristics: major drop in tissue oxygenation (~25-30 %) and NIR perfusion und moderate increase of THI levels

Reperfusion
Duration: 6 mins
Method: –
Characteristics: even oxygenation and NIR perfusion levels, increase in THI levels
The following images reflect the physiological course of the testing sequence.
Comparison of tissue oxygenation in the left (TI-CAM and monitoring device) and the right hand (TI-CAM).

The tissue oxygenation of the left hand (TI-CAM: blue graph, MOXY: grey graph) acquired via TI-CAM and monitoring sensor as well as the oxygenation of the right hand are shown above. The data recorded with the MOXY are nearly identical to the data of the TI-CAM, thus confirming the TI-CAM measurements.

The tissue oxygenation of the left hand (TI-CAM: blue graph, MOXY: grey graph) acquired via TI-CAM and monitoring sensor as well as the oxygenation of the right hand are shown above. The data recorded with the MOXY are nearly identical to the data of the TI-CAM, thus confirming the TI-CAM measurements.

The diagram below shows the TI-CAM parameters: superficial oxygenation, NIR perfusion (deeper oxygenation) and tissue hemoglobin index (THI).

Juxtaposition of the parameters oxygenation, NIR perfusion and THI, which were acquired from the left hand with the TI-CAM during the course of the tests. The increase in THI levels during the venous occlusion is clearly visible, just like the major decrease of tissue oxygenation during the arterial occlusion.

Juxtaposition of the parameters oxygenation, NIR perfusion and THI, which were acquired from the left hand with the TI-CAM during the course of the tests. The increase in THI levels during the venous occlusion is clearly visible, just like the major decrease of tissue oxygenation during the arterial occlusion.

The internal validation study showed the reliability of the measuring data of the TI-CAM. Furthermore, the data is proven by significant findings in expert literature.
In wound care, tissue oxygenation is an important parameter of the healing process. For oxygenation levels higher than ca. 50 %, a positive wound development is very likely. However, wound tissue with a lasting oxygen saturation lower than 30 %, will most likely necrotize because of the insufficient supply. Tissue oxygenation levels below 10 % indicate dead tissue (necrosis). This is shown in the image below. It depicts a wound at the sole of a foot, which has areas with necrotic tissue.

Example of necrotic tissue. The oxygenation of the whole wound area is shown on the left. The circles within the image are software markers, referring to the average tissue oxygenation for the respective circled area (gey: 3 %, pink: 41 %, purple: 8 %). The histogram on the top right shows the acquired data for every pixel within said circles. In parts of the wound, the oxygenation levels are below 10 %, clearly indicating the necrotized tissue. This is visualized in the spectra of the markers (bottom right) as well.

Example of necrotic tissue. The oxygenation of the whole wound area is shown on the left. The circles within the image are software markers, referring to the average tissue oxygenation for the respective circled area (gey: 3 %, pink: 41 %, purple: 8 %). The histogram on the top right shows the acquired data for every pixel within said circles. In parts of the wound, the oxygenation levels are below 10 %, clearly indicating the necrotized tissue. This is visualized in the spectra of the markers (bottom right) as well.

Further information on this topic are provided here: HyperWound-CAM or Flap Monitoring