Patient Tracking System For Smart Hospitals Computer Science Essay

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RFID based identification and tracking have shown tremendous growth in the past few years in various areas, healthcare being the most prominent one. After giving a brief introduction about RFID technology and the existing tracking systems used, this paper demonstrates how the existing tracking systems could be built upon to create a new efficient patient tracking system for smart hospitals. The major components of this tracking system include active RFID tags, readers, access points and control server. The hospital staff and patients are provided with RFID active tags which communicate with the RFID readers placed at strategic locations in the hospital. In addition to this, the staff is also provided with RFID enabled handheld PDAs. The readers pass the tag information to the control server through access points with the help of RFDC system. The control server which is responsible for authentication and location mapping, in turn, communicates with the various wireless devices through wireless LAN. This paper also focuses on the inherent issues with deployment.

Index Terms-RFID medical care, Patient Tracking System, Location tracking, RFID Health Care

INTRODUCTION

According to statistics [1], an average of 98000 people die in the United States alone due to medical errors. These errors could be due to surgical procedures performed on the wrong parts of the body or on the wrong patient. [2] insists that "the problem is not bad people in health care, it is that good people are working in bad systems that need to be made safer". Due to such errors, hospitals end up in losing millions of dollars in doing the reverse procedures to correct those errors. Estimates [3] prove that only about 60% of the hospitals in the United States have a Hospital Information System for maintaining patient records and for provide adequate patient care. It has also been proved further that majority of such hospitals use bar code technology for patient identification, which leaves room for errors due to its drawbacks and limited use. All these facts necessitate the need for an efficient patient tracking system.

Numerous RFID based patient tracking systems are already in use in some hospitals. The details and drawbacks of such systems are discussed in the upcoming sections. Almost all of these systems were designed for a single purpose and hence they are not versatile enough to be used for providing complete patient care. Existing systems also lack sufficient authentication techniques to ensure that the right person gets the right access. This project proposes a new tracking system, built upon the existing systems in use, which when deployed, could provide the adequate patient care and prevents misidentification of surgical patients in the operating rooms.

THE RFID TECHNOLOGY

The basic RFID system consists of RFID tags, readers and backend database for data processing. The data is stored in RFID tags which are similar to barcode labels. They can be attached to or embedded in products. The tag consists of an antenna, with the help of which it communicates with the reader. It also has a small microchip that can store data up to about two kilobytes. The RFID reader works in a way similar to the bar code scanner, with the exception that it uses radio frequency waves for communication. The reader also has an antenna that transmits signals to the tags. The tags, on receiving signals from the readers, transmit the information that it encloses to the readers. The information from the reader is then processed by a back end database system.

RFID tags can be of two types: active and passive. Passive tags do not have any built in power source and hence, cannot initiate communication with the reader. They use the energy from the readers to communicate and hence the read range is less. It typically varies from a few millimeters to about 5 metres. Active tags have built in power source and can initiate communication with the reader. RFID tags can also be classified based upon the type of memory used for storing the data on the chips. The widely used is Read Only Memory. The data is entered into the chip during the time of manufacture and cannot be altered at a later point of time. The other type is Read or Write memory, in which the data, after being entered during the time of manufacture, can be altered as and when needed.

EXISTING PATIENT TRACKING SYSTEMS

VeriMed Patient Identification System

VeriMed Patient Identification system uses VeriChip which was produced by Applied Digital Solutions. VeriChip is a small implantable microchip consisting of a unique identification number. The chip is activated when signals are received from RFID readers. The hospital staff is provided with handheld readers. Only authorized people can get access to patient information from the backend database.

This system is fast and secure and has proven to be very effective in providing adequate care to critical patients. The biggest drawback of this system is that, it is vulnerable to over the air spoofing attacks. Attackers can easily create a spoof device by either eavesdropping on its transmitted signal or by learning its serial number. It has also been found that patients are reluctant to abide by this system due to privacy issues and the possible adverse health effects to the wearers. All the above factors are obstacles to the implementation of this system on a large scale.

Smart WristBands

Smart Wristbands were produced by Precision Dynamics Corporation. The wristbands produced by the company are of two types: Barcode wristbands and RFID Smartbands. RFID Smartbands gained more popularity due to the inherent benefits of RFID technology. The Smartbands store the patient identification data and medical record number. This use of this system provides adequate patient care that includes proper administration of medicines, specimen collection and tracking, surgical site safety, patient billing, blood transfusion and many more. Since critical patient data is stored in the smart wristbands there should be sufficient authentication to prevent unrestricted access to patient information. But this system lacks proper authentication techniques. Also the patients feel that they should be given a chance to decide what information should be included in the bands, while the staff feels that it is not necessary.

SurgiChip

SurgiChip launched by InfoLogix, prevents surgical errors due to patient misidentification. It consists of a label that is embedded with RFID tag. The system also consists of RFID label printers, handheld RFID readers and wireless LAN for transmitting the data captured by the readers to the database. Web based software allows the staff to view the data collected from the tags. The outside of the label has the name of the patient and the surgital site information. The inside of the label is encoded with other relevant information like the date of the surgical procedure, name of surgeon, type of procedure etc. Ecah label has a unique identification number. The label is read by a handheld scanner and the information is confirmed with the patient. On the day of surgery, this information is again confirmed with the patient and the label is attached to the body part of the patient where the procedure is slated to occur. This system fails to work with critically ill patients who are not in a position to identify themselves.

Ultra-Wideband RFID System

Ultra-Wideband RFID system was developed by Parco Wireless. The tags and readers used in this system were developed by Multispectral Solutions. Two types of active tags are used. Asset tags are of the form of 1 inch cubes which can be glued or attached to the equipment to be tracked. Patients and staff are provided with credit card sized tags. The battery of the tags can last upto five years and can be detected by the readers at a range of 600 feet. Due to the use of Ultra-Wideband, all sorts of interferences are removed, as the system operates by emitting short pulses of radio waves. The system can be used for tracking purposes and performs well in hospital environments. But it still lacks sufficient authorization measures and can be subjected to spoofing attacks.

THE PROPOSED SYSTEM MODEL

Fig 1., shows the architecture of the proposed system. The system uses RFID active programmable tags operating at 2.45 GHz. RFID Readers are placed at various locations in the hospital. In addition to this, each operating room is also equipped with a reader. The locations of the readers are fixed and known. The readers operate at a frequency of 2.45 GHz. The read range of this system is estimated to be about 100ft. The hospital staff is also provided with reader enabled PDAs.

Numerous wired and wireless access points are distributed throughout the facility. Some access points are enabled with readers for additional functionalities. All portable data collection equipments like reader enabled PDAs communicate with the control server with the help of Radio Frequency Data Communication System (RFDC). In the RFDC system the access points transmits the data received from the portable data collection equipments to the control server. The operating frequency is 2.45 GHz. The fixed readers communicate with the access points through wireless LAN(802.11g).

The control server is responsible for authentication, location mapping and preventing unauthorized access. It utilizes wireless LAN for communicating with the access points and the various wireless devices in the facility.

Fig 1: The proposed system architecture

SYSTEM COMPONENTS

Transponders

Active transponders have its own power source that powers up the various components of the transponder. The unique ID of the transponder which is 32 bits, is stored in Electronically Programmable Erasable Read Only Memory (EEPROM). The transponder is provided with wired and wireless interfaces for configuration purposes. The flash memory consists of applications that are used by the transponder for its operation. The transponder also has a microcontroller that communicates with the EEPROM, flash memory and the chip which has an antenna for communication with the reader. The chip antenna unit of the transponder also contains a register that stores the value of the strength of the signal received. The transponder unit also has Random Access Memory that stores appropriate functions and data required for operation of the microcontroller.

Fig 2., shows the operation of the transponder. When the transponder is powered up, it first checks whether the received signal strength is above a certain threshold value stored in the transponder. If it is below the threshold value, then the transponder assumes that the reader is busy communicating with other tags. It goes back to the sleep mode. If the signal strength is above the threshold value, the transponder checks if the signal packet is corrupted or not by verifying the checksum value. It then checks the type of request received. If the request is for configuration or programming purpose it goes to the configuration mode. Else it must send a response packet. Before sending the response packet the transponder has to authenticate itself with the reader.

Symmetric key cryptography is used for communication with the reader. The transponder sends its identity to the reader. The reader sends a nonce N to the tag. The tag uses the secret key that it shares with the reader and the nonce N to generate a hash code H, which is sent to the reader. The reader generates the hash code and compares it with the one it has obtained. If it matches, the authentication phase is passed. The transponder then checks if the tag ID mentioned in the packet is correct. If it matches, the microcontroller of the tag generates the response packet and transmits to the reader. The transponder goes back to the sleep mode.Fig 3., shows the structure of the signal packet exchanged between the reader and the tag.

Powered Up

Is SSI > threshold value?

Is packet corrupted?

Is request for config?

Generate response packet

Is authentication passed?

Sleep Mode

Configuration Mode

Yes

Yes

Yes

Yes

No

No

No

No

Is the tag ID correct?

Yes

No

Fig 2. Flowchart for Transponder Operation.

Start of text

Tag ID

Request Type

Device Type

Command Field

Data Length

Status(only used for reply packet)

Time Out

Data

Checksum

Sequence Number

End of text

Fig 3. Signal Packet Format

Readers

This system employs active transponders. Active transponders have its own power source that powers up the various components of the transponder. The unique ID of the transponder which is 32 bits, is stored in Electronically Programmable Erasable Read Only Memory (EEPROM). The transponder is provided with wired and wireless interfaces for configuration purposes.

Fig 4. Flowchart for the Reader Operation

The flash memory consists of applications that are used by the transponder for its operation. The transponder also has a microcontroller that communicates with the EEPROM, flash memory and the chip which has an antenna for communication with the reader. The chip antenna unit of the transponder also contains a register that stores the value of the strength of the signal received. The transponder unit also has Random Access Memory that stores appropriate functions and data required for operation of the microcontroller.

Fig 4., shows the operation of the transponder in listen mode. When the transponder is powered up, it first checks whether the received signal strength is above a certain threshold value stored in the transponder. If it is below the threshold value, then the transponder assumes that the reader is busy communicating with other tags. It goes back to the sleep mode. If the signal strength is above the threshold value, the transponder checks if the signal packet is corrupted or not by verifying the checksum value. It then checks the type of request received. If the request is for configuration or programming purpose it goes to the configuration mode. Else it must send a response packet. Before sending the response packet the transponder has to authenticate itself with the reader.

Access Points

The tracking system has numerous access points distributed throughout the facility. Access points can be wired or wireless. The wireless interface allows communication with various wireless devices in the network. Devices like host computers, laptops, PDAs can connect to the network through access points. The WAN interface of the access point allows communication with other access points over the network. Some access points are enabled with readers that allow it to communicate with nearby transponders.

Each access point has a table of information on the readers that it can communicate with. This information is manually entered into the access point by the administrator at the time of start up. The access point also has a Tag ID table consisting of tag IDs, tag type, reader ID of the reader which obtained this information, the corresponding signal strength value and the time at which this information was entered. This information is transmitted to the control server when requested. The control server can also issue requests to the access points to collect information on certain tags. The access point then issues requests to the appropriate readers to collect the information. If an access point doesn't get to hear from a particular reader during the specified time, then it can issue a warning message to the control server indicating that a particular reader is faulty. The control server then sends alarm messages to the appropriate personnel.

Fig 5. Flowchart for communication between access point and control server.

The control server has a list of the access points that it can communicate with, consisting of the unique ID and IP addresses. It also stores a time out value for each access point. If a response is received from an access point the time out value is reset to zero. Each time it doesn't get a response from an access point, the time out value is increased by one. Eventually after 5 time outs the entry associated with the access point is removed from the list. The server uses a token passing mechanism to communicate with the access points in its list.

The access points send keep alive messages at periodic intervals to the server, as an indication of its availability. The keep alive messages contain information about the access point. Each time the server receives a keep alive message, it checks whether the particular access point is there in its list and whether the information has changed. If the information on a particular access list has changed, then the server updates this information corresponding to the access point entry in the list. If the server doesn't find the access point entry in the list then it indicates that either it is a new access point or an existing one whose entry was removed from the list due to time out. If it is a new access point, then the server adds the entry to its list.

Control Server and Management Facility

The control server consists of numerous host computers running the various applications required for the functionalities provided by the server. Control Server supports location-tracking application, authorization system, alert system and several management related functionalities.

All the tag ids are registered in the control server database before installing them in the system. Location tracking provides the approximate location of the tags. More than one reader can track the same tag. The captured signal strength for a particular tag in each reader may have different values, depending upon the proximity of the tag to the reader. The tag id table in the control server database has an entry for each tag, which has the tag id, signal strength, reader id of the reader that captured information, type of tag and the time at which the entry was added to the table. The location of the readers are fixed and known to the server. To get the X co-ordinate of the tag: the x co-ordinates of all the reporting readers are divided by the total number of reporting readers. Similarly to get the Y co-ordinate of the tag: the y co-ordinates of all the reporting readers are divided by the total number of reporting readers. This weighted average procedure gives the approximate location of the tag in the facility. To get a more accurate location of the tag, triangulation mechanism as mentioned in [11] can be used. But the disadvantage of this mechanism is that it is not cost-effective.

The control server also periodically updates its Tag Data table. Tag Data table has information on all the tags that are used in the facility. It contains tag id, type of tag, description and permission set for each tag. For example, some patients are not supposed to be in close proximity with other patients due to their medical condition. Permission levels are accordingly set for such tag, and if the system detects that the tags are in close proximity then, it sends alert messages to the appropriate staff.

The control server also has list of access points installed in the system, to which it sends token messages as described in the Access Point section. It also has a Reader table, which consists of reader information and list of access points the reader can communicate with. The working of the system is explained in more detail below with the help of few scenarios.

SCENARIOS

Administering medicine to the patients.

When a staff member approaches a patient, the server detects that the tags are in close proximity based on the location. To administer the right dosage to the patient, the nurse scans the medicine with the handheld reader enabled PDA. These details are sent to the control server, which checks if the staff is authorized to administer that medicine to the patient. If the staff member is authorized, the dosage details are sent to the PDA. Once the medicine is administered, the staff member sends a confirmation to the server via the PDA and this information is updated in the patient's record. This prevents the administration of wrong and incorrect dosage of medicines to the patients.

Preventing misidentification of patients in operating rooms

Each OR is equipped with a reader and displays. When a patient is wheeled into the OR, the reader reads the tag and sends the tag information to the control server. The server checks whether that patient is scheduled for a surgical procedure in that OR. If there is a mismatch, alert messages are sent immediately to the displays in the OR. Else the required patient information is sent to the displays.

Scenario 3- Restricting patients to unauthorized areas.

Patients with certain medical conditions, for example dementia, should be prevented from accessing certain areas of the hospital. If a patient wanders into the restricted areas of the hospital, the server would track the tag's location, check the permission level set for the tag and sends alert messages to the appropriate personnel.

Restricting patients to unauthorized areas

Patients with certain medical conditions, for example dementia, should be prevented from accessing certain areas of the hospital. If a patient wanders into the restricted areas of the hospital, the server would track the tag's location, check the permission level set for the tag and sends alert messages to the appropriate personnel.

CONCLUSION

This proposed system architecture is a better and efficient patient management system, which provides adequate patient care with minimal room for errors. The drawback of this system is that it can be a little expensive, as it uses active tags, but it assures better patient safety than the existing RFID systems available.

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