192
N. Blanik
Fig. 11.15 Phenomenon of distributed “blood volume clouds,” observed with PPGI on the forehead
of a subject in sitting position and a relaxed steady state. The post-processed and colored pictures
show perfusion coded images taken at 14, 16, 50, and 69 seconds of a PPGI video sequence [15]
11.4.2 Selective Multi-dimensional Mapping of Vital
Parameters
During the analysis of purely single and often hand-picked ROIs, it is often assumed
that either the extracted vital parameters are valid for the recorded PPGI sequences in
totality, or that a measurement with spatial resolution is unnecessary and therefore,
not worth the effort of calculation. This might be true for vital parameters like the heart
rate where the detected HR—because of the role of the heart as central oscillator—
is not dependent on the measurement spot as long as the chosen ROI is always
positioned on a visible skin region of the same subject. In contrast, however, other
vital parameters like blood perfusion or local thermoregulation, exhibit the property
of spatial distribution, therefore, in order to capture these parameters accurately, a
fixed-size ROI is continuously moved along the image, and for every position, the
appropriate PPG signal (associated with the respective vital parameter) is extracted
and analyzed. These parameters are subsequently assigned to the position of the
ROI, thus creating a functional mapping. This two-dimensional map represents the
image plane of the PPGI frame, with the option of optional third time dimension if
the analyzed parameters are time-dependent. Further dimensions are also possible
according to the dimension of the results. For single snapshots of vital parameters
(e.g., skin perfusion), these mappings are three-dimensional.
An example for such mapping is illustrated in Fig. 11.15. The belonging sequence,
recorded from the forehead of a relaxed, seated subject, shows the location- and
time-dependent skin perfusion. Complicated pattern of appearing and disappearing
“blood volume clouds” become visible. In consequence, the monitored perfusion
N. Blanik
Fig. 11.15 Phenomenon of distributed “blood volume clouds,” observed with PPGI on the forehead
of a subject in sitting position and a relaxed steady state. The post-processed and colored pictures
show perfusion coded images taken at 14, 16, 50, and 69 seconds of a PPGI video sequence [15]
11.4.2 Selective Multi-dimensional Mapping of Vital
Parameters
During the analysis of purely single and often hand-picked ROIs, it is often assumed
that either the extracted vital parameters are valid for the recorded PPGI sequences in
totality, or that a measurement with spatial resolution is unnecessary and therefore,
not worth the effort of calculation. This might be true for vital parameters like the heart
rate where the detected HR—because of the role of the heart as central oscillator—
is not dependent on the measurement spot as long as the chosen ROI is always
positioned on a visible skin region of the same subject. In contrast, however, other
vital parameters like blood perfusion or local thermoregulation, exhibit the property
of spatial distribution, therefore, in order to capture these parameters accurately, a
fixed-size ROI is continuously moved along the image, and for every position, the
appropriate PPG signal (associated with the respective vital parameter) is extracted
and analyzed. These parameters are subsequently assigned to the position of the
ROI, thus creating a functional mapping. This two-dimensional map represents the
image plane of the PPGI frame, with the option of optional third time dimension if
the analyzed parameters are time-dependent. Further dimensions are also possible
according to the dimension of the results. For single snapshots of vital parameters
(e.g., skin perfusion), these mappings are three-dimensional.
An example for such mapping is illustrated in Fig. 11.15. The belonging sequence,
recorded from the forehead of a relaxed, seated subject, shows the location- and
time-dependent skin perfusion. Complicated pattern of appearing and disappearing
“blood volume clouds” become visible. In consequence, the monitored perfusion