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FIELD AND BACKGROUND OF THE INVENTION
This invention relates in general to the construction of probes for
measuring heat transfer of blood circulation of living tissues and, in
particular, to a new and useful probe, including a probe support having a
plurality of alternately arranged layers of thermoelectric conductor
material and insulation formed around the support and forming two
oppositely connected thermocouples, each including an outwardly extending
layer of a thermoelectric material and a common connecting layer of
another thermoelectric material, one of which is heated and arranged in
the range of the probe tip or surface, and the other is unheated and
arranged at a spaced location from the probe tip.
DESCRIPTION OF THE PRIOR ART
Probes for measuring conditions of human tissue are known from German Pat.
No. 956,868, from the book "Durchblutungsmessung mit Waermeleitelmenten"
(Blood circulation measurements with heat conductive elements), by
Golenhofen, Hensel and Hildebrants, Published by Georg Thieme, Stuttgart
(1963), and from DAS No. 1,121,274. These probes are usually arranged
inside metal tubes which impart mechanical stability to the probe and
enclose them tightly.
The individual thermocouple legs, as well as the heating current leads are
designed as thin wires insulated from each other by glass, etc. The
heating is effected by Peltier heating, heating with resistance wires or,
as in the case of the last-mentioned publication, by diathermal heating of
the tissue surrounding the tip of the probe.
A disadvantage of these constructions is the large diameter of the probe
tip, which is due to the design, and which limits the spatial resolution
of the measurement to such an extent that the measurement of
micro-circulation is impossible, and only mean values of the blood
circulation in large tissue sections can be measured. Micro-circulation
is, however, of great interest to the physician. Another disadvantage of
the known probes is the great mass of the probe tip, which leads to a high
thermal capacity, and thus, to a longer response time of the probe. A
further disadvantage is the very great thermal conductivity of the probe,
which requires a large spacing between the two thermocouples to avoid
heating of the unheated thermocouple. This great spacing leads to a great
dependence of the measured value on temperature gradients in the tissue,
for example, on organ surfaces. An attempt to improve the known probes by
reducing the wire thicknesses and by weakening the supporting structure
led to probes which no longer had sufficient mechanical stability.
SUMMARY OF THE INVENTION
The present invention provides a probe which permits maximum spatial
resolution with mechanical stability, and a short response time without
heating the unheated thermocouple.
According to the invention, the outwardly extending leg or layer of the
thermocouple in the range of the probe tip, and the connecting leg or
layer are arranged as thin films, separated by insulating thin films
except for a contact zone, superposed on the surface of an electrically
and thermally insulating pointed supporting body. On the shaft region of
the probe, the connecting leg or layer is contacted with the outwardly
extending leg or layer of a second thermocouple, designed as a thin film.
With the present state of thin film technique, it is possible to apply thin
films of high mechanical stability on very thin, highly stable support
needles, for example, of glass. Probes with a tip diameter of the order of
1 .mu. can be readily produced. Probes with this tip volume have such a
low thermal capacity that the response time can be brought into the range
of the rise time of the required amplifiers. The heating of the unheated
thermocouple by the heated thermocouple is effected substantially by
thermal conduction in the probe and by thermal conduction in the tissue.
The thermal conduction in the probe is very small, however, due to the
extremely high ratios of the surface to the volume, since the probe is
already in thermal equilibrium with the tissue in a small distance from
the heated point. Thermal conduction through the tissue likewise does not
lead to measurable co-heating, since the necessary filament power is
extremely low due to the low thermal capacity. The two thermocouples can
therefore be arranged in an extremely small space of a few 100 .mu.. This
space is sufficiently small, related to the temperature gradients
appearing in the tissue. The spatial resolution of the probe, according to
the invention, is excellent, since the temperature field around the probe
tip is only a few .mu..sup.3, and the accuracy of the measurement is thus
in this range. The probe according to the invention permits maximum
three-dimensioned resolution of the blood circulation profiles of organs.
The invention, for the first time, provides information about the
vascularization and extent of blood circulation in the range of the
smallest blood vessels. Vascular diseases and organic diseases, which
manifest themselves mainly in the range of the smallest vessels, can be
determined in this way. Furthermore, blood circulation profiles of large
vessels can be made, particularly, for intra-operative diagnosis.
From DOS No. 1,907,150, it is also known to design thermocouple legs or
layers in layered construction. In this arrangement, the insulation is
effected by geometric separation of the legs on different sides of an
insulating supporting body. DOS No. 2,247,962 shows a thermocouple where
the legs are made of semiconductor material and are separated by a thin
layer. Miniaturization of the constructions known from these publications
to the desired extent is not possible, however, so that these suggestions
have not found their way into the above cited state of the art.
The probe according to the invention is further advantageously
characterized by the fact that the heating is effected by a resistance
film, insulated from the legs by insulating thin films, and arranged in
the range of the heated thermocouple. The resistance thin film is
separated from the thermocouple only by a very thin insulating thin film,
and it thus brings the filament power into the proximity of the
thermocouple to be heated. But it contributes very little to the thermal
capacity of the tip.
The probe according to the invention is additionally advantageously
characterized by the fact that the resistance thin film is contacted on an
extremely small area with a conductor thin film carrying the heating
current which is electrically insulated from the legs or layers and the
resistance thin film by insulating thin films, this area being inside the
ring-shaped heated thermocouple. In this design, the current flows between
the very small contact surface of the feeder conductor with the resistance
film in diverging current paths through the resistance thin film for its
connecting contacting, so that the maximum current density and, thus, the
maximum filament power appears on the thermocouple. In this way, the
necessary total filament power is reduced and is concentrated exactly to
the desired operation.
Another advantageous feature of the invention is the fact that two
additional thin films of different thermoelectric materials, insulated by
insulating thin films, are contacted with the heated thermocouple in a
mutual type thermocouple. This alternate design of the heating system as a
mutual type thermocouple permits particularly simple, layered construction
of layers of only two materials, whose common contacting in the tip range
can be produced very easily. In this case, the filament power is generated
directly in the thermocouple.
The probe of the invention further advantageously is characterized by the
fact that the support is designed for radiant heating of the heated zone
as a photoconductor whose surface is designed as a reflecting surface,
with the exception of a window arranged in the zone to be heated. Radiant
heating prevents, a priori, any electrical influence of the heating
current on the thermoelectric voltage, as it can occur in electrical
heating. The highly constant radiation source can be readily provided at
the shaft end of the probe, and the heating takes place only in the
desired zone in which the radiation issues from the interior of the
support. The absorption can take place with advantage in the layered
structure above the window, so that a constant absorption is ensured. The
absorption can also take place in a radiation-transmissive layered
structure, or in the absence of a layered structure above the window, in
the absorbent tissue. The radiation issues here into a space sector of the
tissue which is heated down to a certain depth of penetration. The
filament power is generated exactly concentrated directly in the tissue
and need not be transferred from a heating system to the tissue.
The probe according to the invention with electric heating of the tissue by
two electrodes, of which one is very small and arranged in the zone to be
heated, and which corresponds to the design of DAS No. 1,121,274 is
advantageously characterized by the fact that the small electrode is
provided as an exposed panel of a conductor thin film arranged on the
probe, insulatingly covered on the outside, while the other larger
electrode is arranged as an outside conductor thin film on the shaft zone
of the probe. The advantages of electric heating can thus be obtained with
a probe of simple design, according to the invention. The small electrode
can be formed without additional layers by an exposed panel of the outside
thermocouple leg or layer, and with DC heating, the differentiation of the
thermoelectric DC voltage from the AC interference signal can be effected
in a simple manner in the measuring amplifier. The electric heat is
generated again, directly in the tissue, at the point where the current
path has the smallest cross-section, namely, directly in front of the
small electrode. The resistance of the current path, and thus the filament
power, is independent of the movements of the probe, due to the fixed
geometric design.
Furthermore, the probe according to the invention is further characterized
by the fact that the support is designed as a fiber or bundle of fibers
set or grown in the shaft zone. With this design of the probe, it is
possible to achieve extremely thin probe tips of extremely great strength,
if, for example, monocrystalline or polycrystalline inorganic fibers or
fiber bundles are used.
Finally, the probe according to the invention, is characterized by the fact
that at least the heated zone of the probe is coated with a film of low
thermal conductivity. The heated zone is thus thermally screened from the
medium, so that the desired excess temperature of the heated zone can be
maintained with a lower filament power. This coat also serves as corrosion
protection with a suitable selection of the material.
Accordingly, it is an object of the invention to provide a probe for
measuring heat transfer or blood circulation of living tissues, which
comprises, a probe support which has a shaft portion and an end tip with a
probe surface and which has a plurality of alternately arranged layers or
legs of thermoelectric conductive material and insulation formed thereon
adjacent said probe surface, and including two pairs of said conductor
material being in contact at locations spaced from each other and forming
thermocouples with one of the conductive layers being heated and arranged
in the area of the probe tip, and the other being unheated and arranged in
the range of the probe shaft.
A further object of the invention is to provide a probe for measuring heat
transfer or blood circulation of living tissues, which is simple in
design, rugged in construction and economical to manufacture.
The various features of novelty which characterize the invention are
pointed out with particularity in the claims annexed to and forming a part
of this disclosure. For a better understanding of the invention, its
operating advantages and specific objects attained by its uses, reference
should be had to the accompanying drawing and descriptive matter in which
there are illustrated preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
In the Drawings:
FIG. 1 is a cross-sectional view of a probe having radiant heating of the
tissues and constructed in accordance with the invention;
FIG. 2 is a view, similar to FIG. 1, of another embodiment of the
invention;
FIG. 3 is a view, similar to FIG. 1, of still another embodiment of the
invention with resistance film heating; and
FIG. 4 is a view of another embodiment of probe on a much smaller scale and
having a fiber tip.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings in particular, the invention embodied therein in
FIG. 1 comprises a probe, which includes an electrically and thermally
insulated support 60 having a plurality of films disposed over the side
walls thereof in a shaft portion 60a at a location adjacent to a probe tip
having a probe tip surface 67. In accordance with the invention, the
plurality of layers or films include a conductive film 61 which extends
from the inside to the outside of the probe and an insulating film 62
extending over the conductive film 61. A second conductive film 63 is
applied over the insulating film 62. Conductive films 61 and 63 are
superposed in the range of the probe tip adjacent surface 67 at a location
where the insulating film 62 is discontinued, so that they are in direct
electrical contact and form a first thermocouple 66. Conductive film 63
ends in a zone along the probe shaft portion 60a and forms a second
thermocouple 65 in a contact area with an outer conductor film 64. The end
of conductor film 63 is several 100 .mu. behind the tip surface 67 and it
is contacted there by the adjoining third conductor film 64. Thermocouple
65 is formed between the film 63 and 64. Conductor films 64 and 61
comprise the same thermoelectric material and they form two outwardly
extending legs of the thermocouples 65 and 66, respectively. Conductor
film 63 in between comprises a different thermoelectric material and forms
a connecting leg of the two thermocouples 65 and 66. Thermocouple 66 in
the probe tip is thus oppositely connected to thermocouple 65, so that the
difference of the two thermoelectric voltages can be tapped at the
outwardly extending legs formed by films 61 and 64.
Support 60 is advantageously made of a material, such as glass, which is
also suitable as a support for the other embodiments of the probe, because
of its high mechanical strength even with the small diameters that can be
realized with the invention.
The probe tip is cut off at 67 by the film layers, so that radiant energy,
e.g., light, radiated from the probe shaft through support 60, issues to
the outside through the support surface exposed by the surface of the cut.
The light issues only at this point from support 60, since the other parts
of the surface of the probe support act as reflectors, due to the
reflecting properties of the inner film 61 and also by suitable pairing of
the indices of refraction with an additional film arranged directly on the
support surface. The radiant energy thus heats only the volume of the
tissue directly in front of surface 67. Thus, only a volume tissue which
is arranged in the immediate proximity of the ring-shaped thermocouple 66
is thermally influenced, but not the thermocouple 65, which is arranged
further back on the shaft.
The probe, according to FIG. 2, has, on an insulation support 50,
superposed conductor thin films or layers 51, 53, 55 and 57, which are
separated by insulating films or layers 52, 54 and 56. The entire
arrangement is covered by an additional insulating film 58. After the
films 51 to 56 have been applied, the entire arrangement is cut off in the
tip area in a surface of cut 59 so that the conductor film 57 applied
subsequently contacts the surfaces of cut of all underlying conductor
films 51, 53 and 55.
Any two of the conductor films 51, 53, 55 or 57 are designed as a leg and
connecting leg of the thermocouple of the tip area, while the other two
conductor films form the heating legs of the mutual type thermocouple
formed with this arrangement and which consist of four films. The
connecting leg passes over into an outwardly extending thermocouple leg in
a zone (not shown) in an unheated thermocouple arranged farther back on
the shaft.
The outwardly applied insulating layer 58 serves not only as a corrosion
protection, but primarily, as thermal resistance to reduce the heating and
cooling power to be expended, which is required to maintain a certain
over-or under-temperature.
The probe, according to FIG. 3, has on a support 100, a first thermocouple
conductor film 101 extending from the inside to the outside, an insulating
film 102, a second thermoconductor film 103, an insulating film 104, a
connecting conductor film 105 for heating, an insulating film 106, and a
resistance film 107. Above it is applied an additional insulating film 108
which serves the same purposes as film 58 in FIG. 2.
After films 101 and 102 have been applied, the probe tip is broken off in a
surface 109, and the probe shaft and the surface 109 are coated with the
second thermocouple conductor film. In the surface of cut 109, the contact
of the thermocouple is thus established in ring form.
The second conductor film 103 subsequently applied at the front on surface
109 is removed in a recess around the axis 1010; and the insulating film
104, the connecting film 105, and the insulating film 106, are applied.
Then a smaller recess is produced in insulating film 106 around axis 1010,
in which the subsequently applied resistance film 107 makes contact with
the connecting film 105.
In this probe, the filament power is produced substantially only in the
zone directly around the recess or hole in the tip and, thus, in the
immediate proximity of the heated thermocouple. The contacting of the
outer resistance film 107 with an additional outside connecting conductor
(not shown) can take place in a zone of the probe farther back, in which
not much filament power is expended, because the support is much thicker
there and the conductive cross-section of the resistance film 107 is
therefore much greater. The unheated thermocouple (not shown) is also
arranged on the shaft of the probe.
In a variation (not shown) of the embodiment in FIG. 3, the heating can
also be effected by electric heating of the tissue in front of the probe
tip. To this end, the probe represented in FIG. 3 is so designed that the
thermocouple conductor 103 passes in front of the probe tip, and the films
104 to 107 are omitted. A hole or recess is provided short of the probe
tip in the outer insulating film 108 around the axis 1010, which exposes
the surface of film 103. Film 103 is connected, not only to the
thermocouple amplifier, but also to a heating current generator to which
is also connected a large-surfaced thin film electrode arranged on the
probe shaft. A current flows between the electrodes which heats the
tissue, and which has a cross-section which is concentrated in front of
the small electrode surface in the probe tip and then heats the tissue in
front of it with the major part of the filament power.
In another embodiment, the probe tip, according to FIG. 3, can be operated
with radiant heat. In the hole or recess around axis 1010, the reflecting
film 103 which covers the probe, is missing in the surface 109. Radiant
energy conducted through support 100 to the probe tip can issue in this
hole from the support and be absorbed in the overlying film structure.
This probe is characterized again by a very simple layered structure.
FIG. 4 shows a support whose tip and shaft do not consist of the same
material but which has a shaft tube support 121 and an inorganic fiber 120
as a probe tip. This fiber 120 can be a whisker, for example, or a
polycrystalline fiber, or a bundle of fibers. These fibers have great
physical properties.
Fiber 102 is secured in the tip of the shaft tube 121. It has, for example,
a diameter of a few .mu., and is coated during the subequent application
of the layered structure of the probe together with the shaft tube 121
with the layers. The measuring arrangement is provided on the extremely
fine, preferably additionally pointed, fiber tip 120, while the contacting
of the conductor film with connecting wires, is effected on shaft tube 121
in a zone farther back.
In such a probe with fiber tip, the diameter of the probe is extremely
small in the part formed by the fiber up to a considerable distance from
the probe tip. In this way, changes in the blood circulation caused by the
probe are avoided in the measuring range.
While specific embodiments of the invention have been shown and described
in detail to illustrate the application of the principles of the
invention, it will be understood that the invention may be embodied
otherwise without departing from such principles.
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