Detection of when a capsule camera enters into or goes out of a human body and associated operations

Abstract

A method for detecting a capsule camera entering into or exiting the GI tract, includes (a) taking a first test image under the condition that an illumination system of the capsule camera is disabled; (b) taking a second test image under the same condition as the first test image; (c) comparing selected corresponding pixel values of the first test image and the second test image to determine if a significant change in pixel values has occurred; and (d) upon detecting the significant change in pixel values, determining if the capsule camera has entered or exited the GI tract, and performing operations appropriate to follow such determination.

I claim: 
     
         1 . A method for detecting a capsule camera entering into or exiting the GI tract, comprising:
 operating the capsule camera to take a plurality of images along the GI tract;   using a sensing circuit in the capsule camera that is sensitive to an environmental difference between the GI tract and an environment outside of a human body, determining whether or not the capsule camera has exited the GI tract; and   upon determining that the capsule camera has exited the GI tract, deleting a predetermined number of the images taken immediately preceding the determination.   
     
     
         2 . The method of  claim 1 , wherein the sensing circuit comprises an image sensor array for capturing the images, wherein the image sensor array (i) takes a test image under a condition that an illumination system of the capsule camera is disabled, (ii) determining whether or not a function computed based on selected pixel values of the test image exceeds a predetermine threshold. 
     
     
         3 . The method of  claim 2  wherein the predetermined threshold is determined using a previously obtained test image. 
     
     
         4 . The method of  claim 2 , wherein the selected pixel values correspond to data in a subset of the image sensor array. 
     
     
         5 . The method of  claim 2 , wherein the function computed is based on selected pixel values relates to a red component in the test image. 
     
     
         6 . The method of  claim 1 , wherein the sensing circuit comprises a semiconductor thermometer. 
     
     
         7 . The method of  claim 1 , wherein the environmental difference is detected by comparing a temperature measured by the semiconductor thermometer against a predetermined range. 
     
     
         8 . The method of  claim 7  further comprising calibrating the capsule camera under test conditions to determine the predetermined range. 
     
     
         9 . The method of  claim 8 , wherein results of the calibrating step are recorded in a storage device in the capsule camera for subsequent retrieval. 
     
     
         10 . The method of  claim 8 , wherein a separate predetermined range is determined for each test condition. 
     
     
         11 . The method of  claim 7 , where the predetermined range is stored in a storage device in the capsule camera. 
     
     
         12 . The method of  claim 6 , wherein the environmental difference is detected by comparing temperature measurements taken at different times. 
     
     
         13 . The method of  claim 6 , wherein the semiconductor thermometer detects a temperature change based on a leakage current in a PN junction. 
     
     
         14 . The method of  claim 13 , further comprising pre-charging the PN junction by applying a reverse bias voltage across the PN junction, and measuring a voltage of the PN junction after a predetermined time period. 
     
     
         15 . The method of  claim 14 , further comprising providing an analog-to-digital converter to provide a read-out of the voltage. 
     
     
         16 . The method of  claim 15 , wherein the predetermined period is set by the sampling time of the voltage at the analog-to-digital converter. 
     
     
         17 . The method of  claim 6 , wherein the semiconductor thermometer detects a change in temperature based on a temperature-dependence in a channel current of an MOS transistor. 
     
     
         18 . The method of  claim 6 , wherein the semiconductor thermometer detects a change in temperature based on a difference in temperature-dependence among a plurality of MOS transistors. 
     
     
         19 . The method of  claim 18 , wherein the difference in temperature-dependence arises from a difference in channel length among the MOS transistors. 
     
     
         20 . The method of  claim 18 , wherein the MOS transistors comprise a first set of one or more devices connected in series with a second set of one or more devices, wherein each set of devices has a common temperature-dependence, but the temperature-dependence of the first of devices is different than the temperature-dependence of the second set of devices. 
     
     
         21 . The method of  claim 20 , wherein the first set of devices comprises one or more short channel transistors, and wherein the second set of devices comprises one or more long channel devices. 
     
     
         22 . The method of  claim 20 , wherein the first set of devices are each biased to operate within a linear region, and wherein the second set of devices are biased to operate in a saturation region. 
     
     
         23 . The method of  claim 22 , further comprising a digital-to-analog converter sensing a voltage at an electrical node between the first set of devices and the second set of devices. 
     
     
         24 . The method as in  claim 20 , wherein the first and second sets of devices operate with a strong inversion layer. 
     
     
         25 . The method of  claim 1  further comprising activating an audio signal to indicate the capsule camera has exited the GI tract. 
     
     
         26 . The method of  claim 1 , wherein the capsule camera stores the images in an on-board archival memory. 
     
     
         27 . The method of  claim 1 , wherein the capsule camera transmits the images by wireless as the images are taken, and as the capsule camera travels along the GI tract. 
     
     
         28 . The method of  claim 1 , further comprising recording each time the function exceeds the predetermined threshold in a history record of an on-board storage device, and examining the history record in a power-on self-test. 
     
     
         29 . The method of  claim 28 , wherein the power-on self-test comprises a self-diagnosing function. 
     
     
         30 . The method of  claim 1 , further comprising enabling a lighting pattern using an illumination system in the capsule camera upon the determination that the capsule camera has exited the GI tract. 
     
     
         31 . An integrated circuit, comprising:
 a semiconductor thermometer; and   a control circuit which detects an environmental difference during operation of the integrated circuit using the semiconductor thermometer.   
     
     
         32 . The integrated circuit of  claim 31 , wherein the control circuit detects the environmental difference by comparing a temperature measured by the semiconductor thermometer against a predetermined range. 
     
     
         33 . The integrated circuit of  claim 31 , wherein the control circuit calibrates the semiconductor thermometer under test conditions. 
     
     
         34 . The integrated circuit of  claim 33 , further comprising a storage device in which calibration results under the test conditions are recorded. 
     
     
         35 . The integrated circuit of  claim 34 , wherein a separate predetermined range is recorded for each test condition. 
     
     
         36 . The integrated circuit of  claim 31 , wherein the control circuit detects the environmental difference by comparing temperature measurements taken at different times. 
     
     
         37 . The integrated circuit of  claim 31 , wherein the semiconductor thermometer detects a temperature change based on a leakage current in a PN junction. 
     
     
         38 . The integrated circuit of  claim 37 , further comprising a pre-charging circuit that applies a reverse bias voltage across the PN junction, wherein the control circuit measures a voltage of the PN junction after a predetermined time period of the reverse bias voltage being applied. 
     
     
         39 . The integrated circuit of  claim 38 , further comprising an analog-to-digital converter which provides the control circuit a read-out of the voltage being measured. 
     
     
         40 . The integrated circuit of  claim 39 , wherein the predetermined period is set by the sampling time of the voltage at the analog-to-digital converter. 
     
     
         41 . The integrated circuit of  claim 31 , wherein the semiconductor thermometer detects a change in temperature based on a temperature-dependence in a channel current of an MOS transistor. 
     
     
         42 . The integrated circuit of  claim 31 , wherein the semiconductor thermometer detects a change in temperature based on a difference in temperature-dependence among a plurality of MOS transistors. 
     
     
         43 . The integrated circuit of  claim 42 , wherein the difference in temperature-dependence arise from a difference in channel length among the MOS transistors. 
     
     
         44 . The integrated circuit of  claim 42 , wherein the MOS transistors comprise a first set of one or more devices connected in series with a second set of one or more devices, wherein each set of devices has a common temperature-dependence, but the temperature-dependence of the first of devices is different than the temperature-dependence of the second set of devices. 
     
     
         45 . The integrated circuit of  claim 44 , wherein the first set of devices comprise one or more short channel transistors, and wherein the second set of devices comprise one or more long channel devices. 
     
     
         46 . The integrated circuit of  claim 44 , wherein the first set of devices are each biased to operate within a linear region, and wherein the second set of devices are biased to operate in a saturation region. 
     
     
         47 . The integrated circuit of  claim 46 , further comprising a digital-to-analog converter which receives a voltage at an electrical node between the first set of devices and the second set of devices. 
     
     
         48 . The integrated circuit of  claim 44 , wherein the first and second sets of devices operate with a strong inversion layer. 
     
     
         49 . The integrated circuit of  claim 31 , further comprising an array of non-volatile memory cells. 
     
     
         50 . The integrated circuit of  claim 31 , wherein the control circuit performs a power-on self-test. 
     
     
         51 . The integrated circuit of  claim 50 , wherein the power-on self-test comprises a self-diagnosing function.