Control feedback device for patient incontinence in radiotherapy and body fluid management method

Abstract

The invention discloses a control feedback device for patient incontinence in radiotherapy and a body fluid management method, and relates to the technical field of medical treatment. The problem that a radiotherapy therapist cannot timely discover after incontinence of a patient can be effectively solved, the state of the patient can be better confirmed, body fluid can be better collected, the body fluid of the patient can be prevented from affecting work of an accelerator, follow-up nursing and treatment work of the patient is facilitated, the accelerator is protected from being affected by the body fluid of the patient, and the service life of the accelerator is prolonged. And the radiotherapy work can be carried out orderly, so that the radiotherapy efficiency can be improved.

Description

Technical Field

[0001] The present invention relates to the field of medical technology, and in particular to a control feedback device and a body fluid management method for incontinence of patients during radiotherapy. Background Art

[0002] Radiotherapy is mainly achieved through medical linear accelerators. Medical linear accelerators refer to products that are composed of treatment heads, accelerating tubes, magnetrons / klystrons, collimators, positioning systems, treatment beds, control systems, modulators, water cooling units and other components, and are used for clinical conventional X-ray or electron beam radiotherapy. At present, radiotherapy generally focuses on cancer patients, who have a large heterogeneity with the normal population, and there is also heterogeneity within this population. Therefore, when treating this type of patients, there are more and more complex matters that need to be paid attention to than other patients.

[0003] When patients with tumors are given radiotherapy, they may suffer from incontinence. At this time, body fluids may affect the operation of the treatment bed. When the accelerator rack is transferred to the bottom of the treatment bed, if body fluids drip into the head of the machine, water may enter the accelerator and damage the components. When components are damaged or the humidity inside the machine is high, the treatment of other patients may be delayed during the period of repairing the accelerator and waiting for the humidity to decrease. When patients with tubes undergo radiotherapy, if the gastric tube, urinary catheter, or stool bag is not closed tightly, the above situation may also occur. Therefore, it is necessary to improve the treatment bed board, manage the leaked patient body fluids, and remind the radiotherapists to check the patient's status. Summary of the invention

[0004] The object of the present invention is to provide a control feedback device and a body fluid management method for patient incontinence during radiotherapy, so as to improve the above technical problems.

[0005] In order to achieve the above-mentioned object of the invention, the embodiment of the present invention provides the following technical solutions:

[0006] A control feedback device for incontinence of a patient during radiotherapy comprises a treatment bed, a urine collection device, a first photoelectric detection receptor and a second photoelectric detection receptor;

[0007] A groove is provided in the middle of the upper surface of the treatment bed; the urine collection device is placed at the tail of the groove; the first photoelectric detection sensor is placed at the tail of the groove and connected to the buckle on the top outer side of the urine collection device; the second photoelectric detection sensor is placed on the top outer side of the urine collection device and is adjacent to the buckle.

[0008] Furthermore, the bottom of the groove is inclined from the head of the treatment bed to the tail of the treatment bed to form an inclined plane; and a round hole is provided at the tail of the groove.

[0009] Furthermore, the urine collection device includes a drainage tube and a disposable urine collection bag; one end of the drainage tube is connected to the groove through a circular hole; the disposable urine collection bag is placed at the other end of the drainage tube, and the buckle placed on the outer side of the top of the disposable urine collection bag is used as an opening control switch of the disposable urine collection bag.

[0010] A method for fluid management for incontinence in patients undergoing radiation therapy comprises:

[0011] S1. Give the patient radiotherapy;

[0012] S2, obtaining a corresponding photoelectric detection result through a first photoelectric detection sensor;

[0013] S3, based on the photoelectric detection result, transmitting an incontinence signal to the buckle;

[0014] S4, opening the urine collection device through the buckle;

[0015] S5, monitoring the urine collection device through a second photoelectric detection sensor to obtain a corresponding incontinence monitoring result;

[0016] S6. Control the treatment bed based on the incontinence monitoring results.

[0017] Further, the first photoelectric detection sensor includes a transmitter, a receiver and a detection module;

[0018] The obtaining of the corresponding photoelectric detection result by the first photoelectric detection sensor includes:

[0019] S2-1, emitting a light beam to the groove through the emitter of the first photoelectric detection sensor;

[0020] S2-2, receiving the corresponding first optical signal through the receiver of the first photoelectric detection receptor and converting it to obtain a corresponding electrical signal;

[0021] S2-3. Detect the electrical signal through the detection module of the first photoelectric detection receptor to obtain the photoelectric detection result; wherein the photoelectric detection result is that the patient has incontinence or the patient has not incontinence.

[0022] Further, transmitting an incontinence signal to the buckle based on the photoelectric detection signal includes:

[0023] When the photoelectric detection result shows that the patient is incontinent, the incontinence signal is sent to the buckle, that is, a pop-up signal is sent to the buckle; when the photoelectric detection result shows that the patient is not incontinent, the process returns to S2.

[0024] Further, the second photoelectric detection sensor includes a transmitter, a receiver, and a flow time and urine volume calculation module;

[0025] The method of monitoring the urine collection device by the second photoelectric detection sensor to obtain the corresponding incontinence monitoring result includes:

[0026] S5-1, setting an alarm strategy; wherein the alarm strategy includes an alarm type, a time window, and body fluid threshold data;

[0027] S5-2, emitting laser light to the urine collection device through the emitter of the second photodetector;

[0028] S5-3, receiving the corresponding second optical signal through the receiver of the second photodetector and preprocessing it to obtain a preprocessed second optical signal;

[0029] S5-4, based on the pre-processed second light signal, calculating the corresponding urine flow time and urine volume by the flow time and urine volume calculation module;

[0030] S5-5. Based on the alarm strategy, the urine flow time and the urine volume are judged to obtain the incontinence monitoring result.

[0031] Furthermore, the setting of the alarm strategy includes:

[0032] S5-1-1. Collect radiation patient data and set up initial alarm strategies;

[0033] S5-1-2. Optimize the initial alarm strategy using an adaptive threshold adjustment algorithm to obtain an optimized alarm strategy, namely, the alarm strategy.

[0034] Furthermore, the alarm type includes single alarm, continuous alarm and graded alarm; when the alarm type is single alarm or continuous alarm, the body fluid threshold data is the first body fluid threshold; when the alarm type is a graded alarm, the body fluid threshold data includes the first body fluid threshold to the nth body fluid threshold.

[0035] Furthermore, the controlling of the treatment bed based on the incontinence monitoring result includes:

[0036] S6-1, determining whether the alarm type is a single alarm; if so, issuing a warning through the alarm device, and feeding back the incontinence monitoring result and the urine volume to the control room, and the medical staff controls the treatment bed, that is, suspends the radiotherapy, adjusts the tilt angle of the treatment bed, and replaces the drainage tube and the urine collection device; otherwise, proceeding to S6-2;

[0037] S6-2, determining whether the alarm type is a continuous alarm; if so, continuously issuing a warning through the alarm device, and feeding back the incontinence monitoring result and the urine volume to the control room, and the medical staff controls the treatment bed, that is, suspends the radiotherapy, adjusts the tilt angle of the treatment bed, and replaces the drainage tube and the urine collection device; otherwise, proceeding to S6-3;

[0038] S6-3. When the urine volume exceeds the first body fluid threshold to the n-1th body fluid threshold in sequence, a warning is issued in real time through the alarm device, and the inclination angle of the treatment bed is adjusted; when the urine volume exceeds the nth body fluid threshold, a stop signal is output to the treatment bed through the second photodetector.

[0039] The beneficial effects of the present invention are:

[0040] This device can not only effectively solve the problem that radiotherapists cannot promptly detect incontinence in patients, but can also better confirm the patient's condition and collect body fluids. It can also prevent the patient's body fluids from affecting the work of the accelerator, which is beneficial to the patient's subsequent care and treatment, protects the accelerator from being affected by the patient's body fluids, and ensures the orderly progress of radiotherapy, thereby helping to improve the efficiency of radiotherapy.

[0041] The present invention utilizes sensors to rapidly detect and calculate body fluids, and performs graded warnings according to early warning strategies, thereby timely detecting patient incontinence and promptly reminding therapists to pay attention to the patient's status. In addition, after receiving the alarm signal, the therapist handles the patient's incontinent body fluids to prevent damage to the linear accelerator, reduce the maintenance rate of the device, avoid delaying the radiotherapy of other patients, and improve the efficiency of radiotherapy. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 is a schematic diagram of a control feedback device in an embodiment of the present invention;

[0044] Figure 2A side view of a control feedback device in an embodiment of the present invention;

[0045] Figure 3 Flow chart of the method in the embodiment of the present invention. DETAILED DESCRIPTION

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention.

[0047] See also Figure 1 , a control feedback device for incontinence of a patient during radiotherapy provided in this embodiment includes a treatment bed, a urine collection device, a first photoelectric detection receptor and a second photoelectric detection receptor;

[0048] A groove is provided in the middle of the upper surface of the treatment bed; the urine collection device is placed at the tail of the groove; the first photoelectric detection sensor is placed at the tail of the groove and connected to the buckle on the top outer side of the urine collection device; the second photoelectric detection sensor is placed on the top outer side of the urine collection device and is adjacent to the buckle.

[0049] like Figure 2 As shown, the bottom of the groove is inclined from the head of the treatment bed to the tail of the treatment bed to form an inclined plane; and a round hole is provided at the tail of the groove.

[0050] The urine collection device comprises a drainage tube and a disposable urine collection bag; one end of the drainage tube is connected to the groove through a circular hole; the disposable urine collection bag is placed at the other end of the drainage tube, and a buckle placed on the outer side of the top of the disposable urine collection bag is used as an opening control switch of the disposable urine collection bag.

[0051] This device can not only effectively solve the problem that radiotherapists cannot promptly detect incontinence in patients, but can also better confirm the patient's condition and collect body fluids. It can also prevent the patient's body fluids from affecting the work of the accelerator, which is beneficial to the patient's subsequent care and treatment, protects the accelerator from being affected by the patient's body fluids, and ensures the orderly progress of radiotherapy, thereby helping to improve the efficiency of radiotherapy.

[0052] In addition, corresponding Bluetooth can be installed on the urine collection device, the first photoelectric detection receptor and the second photoelectric detection receptor, and communication connection can be established. Bluetooth has the advantages of convenience, high efficiency, low power consumption and safety. Signals are received and transmitted via Bluetooth, and Bluetooth receiving software is set up in the control room, so that therapists can transmit data with the control feedback device in the operation room through the software, and control, inspect and maintain the working conditions of sensors and other components. Setting up Bluetooth can provide a stable and low-latency transmission channel for the control feedback device, which is convenient for obtaining accurate information prompts during treatment. During use, adjust the parameter settings of the Bluetooth module according to actual needs to achieve optimal performance.

[0053] like Figure 3 As shown, a method for fluid management for incontinence in a patient undergoing radiation therapy comprises:

[0054] S1. Give the patient radiotherapy;

[0055] S2, obtaining a corresponding photoelectric detection result through a first photoelectric detection sensor;

[0056] The first photoelectric detection sensor includes a transmitter, a receiver and a detection module;

[0057] The obtaining of the corresponding photoelectric detection result by the first photoelectric detection sensor includes:

[0058] S2-1, emitting a light beam to the groove through the emitter of the first photoelectric detection sensor;

[0059] S2-2, receiving the corresponding first optical signal through the receiver of the first photoelectric detection receptor and converting it to obtain a corresponding electrical signal;

[0060] S2-3. Detect the electrical signal through the detection module of the first photoelectric detection receptor to obtain the photoelectric detection result; wherein the photoelectric detection result is that the patient has incontinence or the patient has not incontinence.

[0061] S3, based on the photoelectric detection result, transmitting an incontinence signal to the buckle;

[0062] The method of transmitting an incontinence signal to the buckle based on the photoelectric detection signal comprises:

[0063] When the photoelectric detection result shows that the patient is incontinent, the incontinence signal is sent to the buckle, that is, a pop-up signal is sent to the buckle; when the photoelectric detection result shows that the patient is not incontinent, the process returns to S2.

[0064] S4, opening the urine collection device through the buckle;

[0065] S5, monitoring the urine collection device through a second photoelectric detection sensor to obtain a corresponding incontinence monitoring result;

[0066] The second photoelectric detection sensor includes a transmitter, a receiver, a flow time and a urine volume calculation module;

[0067] The method of monitoring the urine collection device by the second photoelectric detection sensor to obtain the corresponding incontinence monitoring result includes:

[0068] S5-1, setting an alarm strategy; wherein the alarm strategy includes an alarm type, a time window, and body fluid threshold data;

[0069] The alarm types include single alarm, continuous alarm and graded alarm; when the alarm type is single alarm or continuous alarm, the body fluid threshold data is the first body fluid threshold; when the alarm type is a graded alarm, the body fluid threshold data includes the first body fluid threshold to the nth body fluid threshold.

[0070] The setting of the alarm strategy includes:

[0071] S5-1-1. Collect radiation patient data and set up an initial alarm strategy; for example, determine the initial alarm type, initial time window, and initial body fluid threshold data based on the patient's corresponding historical treatment time, historical body fluid discharge frequency, and historical body fluid discharge volume; because the setting of the time window will affect the control of the control feedback device, further reducing the corresponding sensitivity, and thus reducing the accuracy of the early warning, it is impossible to detect the changing factors in time, and thus it is necessary to determine the corresponding time window based on historical documents and patient medical records and other information.

[0072] S5-1-2, optimize the initial alarm strategy using an adaptive threshold adjustment algorithm to obtain an optimized alarm strategy, i.e., the alarm strategy. Since the alarm system analyzes and alarms the data of the second photoelectric liquid level sensor, and the second photoelectric liquid level sensor analyzes the amount of body fluid in the collection bag, there may be errors in this link, so it is necessary to automatically adjust the threshold parameters based on historical data, real-time feedback, and dynamic changes of the system to make the alarm strategy more sensitive and accurate, better adapt to the urine bag collection volume and urine flow rate, and improve the accuracy and efficiency of the alarm.

[0073] S5-2, emitting laser light to the urine collection device through the emitter of the second photodetector;

[0074] S5-3, receiving the corresponding second optical signal through the receiver of the second photodetector and preprocessing it to obtain a preprocessed second optical signal;

[0075] S5-4. Based on the pre-processed second light signal, the corresponding urine flow time and urine volume are calculated by the flow time and urine volume calculation module; in an actual application environment, a pressure sensor can be installed at the bottom or head of the urine collection device as needed to further improve the accuracy of the calculation of the urine volume and prevent false alarms.

[0076] S5-5. Based on the alarm strategy, the urine flow time and the urine volume are judged to obtain the incontinence monitoring result. Determine whether the urine volume is greater than any of the body fluid thresholds from the first body fluid threshold to the nth body fluid threshold; when the urine volume is less than the mth body fluid threshold and the urine flow time is less than the time threshold, the corresponding incontinence monitoring result is "the urine volume has not reached the dangerous threshold", and return to S5-1; when the urine volume is greater than the mth body fluid threshold or the urine flow time is greater than the time threshold, the corresponding incontinence monitoring result is "the urine volume has reached the dangerous threshold or the urine flow time has exceeded the time threshold", and further control is required to enter S6.

[0077] S6. Control the treatment bed based on the incontinence monitoring results.

[0078] The controlling of the treatment bed based on the incontinence monitoring result includes:

[0079] S6-1. Determine whether the alarm type is a single alarm; if so, issue a warning through the alarm device, and feed back the incontinence monitoring result and the urine volume to the control room, and the medical staff controls the treatment bed, that is, suspends radiotherapy, adjusts the inclination angle of the treatment bed, and replaces the drainage tube and the urine collection device; otherwise, enter S6-2; wherein, the alarm device is an existing device, so no detailed description is given.

[0080] S6-2, determining whether the alarm type is a continuous alarm; if so, continuously issuing a warning through the alarm device, and feeding back the incontinence monitoring result and the urine volume to the control room, and the medical staff controls the treatment bed, that is, suspends the radiotherapy, adjusts the tilt angle of the treatment bed, and replaces the drainage tube and the urine collection device; otherwise, proceeding to S6-3;

[0081] S6-3. When the urine volume exceeds the first body fluid threshold to the n-1th body fluid threshold in sequence, a warning is issued in real time through the alarm device, and the inclination angle of the treatment bed is adjusted; when the urine volume exceeds the nth body fluid threshold, a stop signal is output to the treatment bed through the second photodetector.

[0082] In addition, an upper or lower limit of the number of alarms can be set, or parameters such as the length of the time window or the alarm threshold can be dynamically adjusted according to the patient's incontinence characteristics, so that the present invention is more in line with the physical condition of each patient and is conducive to assisting therapists in treating them.

[0083] The present invention utilizes sensors to detect and calculate body fluids, and performs graded warnings according to early warning strategies, so as to timely detect patient incontinence and promptly remind therapists to pay attention to the patient's status. In addition, after receiving the alarm signal, the therapist handles the patient's incontinent body fluids to prevent damage to the linear accelerator, reduce the maintenance rate of the device, avoid delaying the radiotherapy of other patients, and improve the efficiency of radiotherapy.

[0084] The method also includes S3-5:

[0085] S3-5-1, receiving the current command from the control room, and setting the state of the first photoelectric detection sensor to "monitoring" and initializing the liquid detection time;

[0086] S3-5-2, based on the photoelectric detection result, determine whether the first photoelectric detection sensor detects urine; if so, add 1 to the counter and enter S3-5-3; otherwise, return to S2; wherein the initial value of the counter is 0;

[0087] S3-5-3, determine whether the counter exceeds 3; if so, enter S4; otherwise, reset the counter and set the state of the first photoelectric detection sensor to "paused" to wait for the next instruction from the control room. This step can further improve the accuracy of the body fluid management method, effectively control the sensor to detect body fluids, and reduce the error rate.

[0088] In addition, the first photodetector in the present invention can replace the function of the second photodetector, and can not only be used to control the buckle and then control the switch of the urine collection device, but also can be used to calculate the urine flow time and body fluid volume, which can further reduce the cost of the device, simplify the complexity of the device, and be suitable for application environments with narrow space, thereby increasing the use scenarios of the device.

[0089] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A control feedback device for incontinence of patients during radiotherapy, characterized in that: It includes a treatment bed, a urine collection device, a first photoelectric detection receptor and a second photoelectric detection receptor; A groove is provided in the middle of the upper surface of the treatment bed; the urine collection device is placed at the tail of the groove; the first photoelectric detection sensor is placed at the tail of the groove and connected to the buckle on the top outer side of the urine collection device; the second photoelectric detection sensor is placed on the top outer side of the urine collection device and is adjacent to the buckle.

2. The control feedback device for patient incontinence during radiotherapy according to claim 1, characterized in that: The bottom of the groove is inclined from the head of the treatment bed to the tail of the treatment bed to form an inclined plane; and a round hole is provided at the tail of the groove.

3. The control feedback device for patient incontinence during radiotherapy according to claim 2, characterized in that: The urine collection device comprises a drainage tube and a disposable urine collection bag; one end of the drainage tube is connected to the groove through a circular hole; the disposable urine collection bag is placed at the other end of the drainage tube, and a buckle placed on the outer side of the top of the disposable urine collection bag is used as an opening control switch of the disposable urine collection bag.

4. A method for managing body fluids for incontinence in patients undergoing radiotherapy, used to implement a control feedback device for incontinence in patients undergoing radiotherapy as described in any one of claims 1 to 3, characterized in that: include: S1. Give the patient radiotherapy; S2, obtaining a corresponding photoelectric detection result through a first photoelectric detection sensor; S3, based on the photoelectric detection result, transmitting an incontinence signal to the buckle; S4, opening the urine collection device through the buckle; S5, monitoring the urine collection device through a second photoelectric detection sensor to obtain a corresponding incontinence monitoring result; S6. Control the treatment bed based on the incontinence monitoring results.

5. The method for managing body fluids for incontinence in patients undergoing radiotherapy according to claim 4, characterized in that: The first photoelectric detection sensor includes a transmitter, a receiver and a detection module; The obtaining of the corresponding photoelectric detection result by the first photoelectric detection sensor includes: S2-1, emitting a light beam to the groove through the emitter of the first photoelectric detection sensor; S2-2, receiving the corresponding first optical signal through the receiver of the first photoelectric detection receptor and converting it to obtain a corresponding electrical signal; S2-3. Detect the electrical signal through the detection module of the first photoelectric detection receptor to obtain the photoelectric detection result; wherein the photoelectric detection result is that the patient has incontinence or the patient has not incontinence.

6. The method for managing body fluids for incontinence in patients undergoing radiotherapy according to claim 5, characterized in that: The method of transmitting an incontinence signal to the buckle based on the photoelectric detection signal comprises: When the photoelectric detection result shows that the patient is incontinent, the incontinence signal is sent to the buckle, that is, a pop-up signal is sent to the buckle; when the photoelectric detection result shows that the patient is not incontinent, the process returns to S2.

7. The method for managing body fluids for incontinence in patients undergoing radiotherapy according to claim 5, characterized in that: The second photoelectric detection sensor includes a transmitter, a receiver, a flow time and a urine volume calculation module; The method of monitoring the urine collection device by the second photoelectric detection sensor to obtain the corresponding incontinence monitoring result includes: S5-1, setting an alarm strategy; wherein the alarm strategy includes an alarm type, a time window, and body fluid threshold data; S5-2, emitting laser light to the urine collection device through the emitter of the second photodetector; S5-3, receiving the corresponding second optical signal through the receiver of the second photodetector and preprocessing it to obtain a preprocessed second optical signal; S5-4, based on the pre-processed second light signal, calculating the corresponding urine flow time and urine volume by the flow time and urine volume calculation module; S5-5. Based on the alarm strategy, the urine flow time and the urine volume are judged to obtain the incontinence monitoring result.

8. The method for managing body fluids for incontinence in patients undergoing radiotherapy according to claim 7, characterized in that: The setting of the alarm strategy includes: S5-1-1. Collect radiation patient data and set up initial alarm strategies; S5-1-2. Optimize the initial alarm strategy using an adaptive threshold adjustment algorithm to obtain an optimized alarm strategy, namely, the alarm strategy.

9. The method for managing body fluids for incontinence in patients undergoing radiotherapy according to claim 7, characterized in that: The alarm types include single alarm, continuous alarm and graded alarm; when the alarm type is single alarm or continuous alarm, the body fluid threshold data is the first body fluid threshold; when the alarm type is a graded alarm, the body fluid threshold data includes the first body fluid threshold to the nth body fluid threshold.

10. The method for managing body fluids for incontinence in patients undergoing radiotherapy according to claim 9, characterized in that: The controlling of the treatment bed based on the incontinence monitoring result includes: S6-1, determining whether the alarm type is a single alarm; if so, issuing a warning through the alarm device, and feeding back the incontinence monitoring result and the urine volume to the control room, and the medical staff controls the treatment bed, that is, suspends the radiotherapy, adjusts the tilt angle of the treatment bed, and replaces the drainage tube and the urine collection device; otherwise, proceeding to S6-2; S6-2, determining whether the alarm type is a continuous alarm; if so, continuously issuing a warning through the alarm device, and feeding back the incontinence monitoring result and the urine volume to the control room, and the medical staff controls the treatment bed, that is, suspends the radiotherapy, adjusts the tilt angle of the treatment bed, and replaces the drainage tube and the urine collection device; otherwise, proceeding to S6-3; S6-3. When the urine volume exceeds the first body fluid threshold to the n-1th body fluid threshold in sequence, a warning is issued in real time through the alarm device, and the inclination angle of the treatment bed is adjusted; when the urine volume exceeds the nth body fluid threshold, a stop signal is output to the treatment bed through the second photodetector.

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