First published online May 25, 2006
British Journal of Radiology (2006) 79, 666-671
© 2006 British Institute of Radiology
doi: 10.1259/bjr/11861604
Building an anonymized catalogued radiology museum in PACS: a feasibility study
A P Toms, FRCS, FRCR,
B Kasmai, MSc, MIPEM,
S Williams, MRCP, FRCR and
P Wilson, MRCP, FRCR
Department of Radiology, Norfolk & Norwich University Hospital NHS Trust, Colney Lane, Norwich, Norfolk NR4 7UY, UK
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Abstract
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The aim of this study was to test the feasibility of a software application that would allow the anonymization and cataloguing of whole DICOM datasets in order to build searchable radiology museums within PACS. The application was developed on a dedicated networked PC, using C# and HL7 coding. Whole DICOM datasets were pushed from PACS to a networked PC on which the application, Museum Builder, was developed. Museum Builder works by replacing the patient specific data (the forename, surname and hospital number) within each header of each DICOM file with terms from anatomical and surgical sieve menus. The date of birth is anonymized to 1 January of the same year. Whole DICOM datasets comprising hundreds of images can be anonymized and catalogued in a single episode. Museum Builder primes PACS with an HL7 script to receive a "new" patient. DICOM datasets are then pushed back to PACS where they are added to the database as "new" cases. The museum cases can then be searched for, on PACS, by any combination of terms that correspond to appropriate anatomical units, surgical sieve headings or radiological specialty. New radiology reports containing clinical histories, radiological descriptions, differential diagnoses and discussion can be added through the report window. Our institution has developed and used this tool to generate a PACS based radiology museum containing not only full DICOM datasets, but also relevant histological and clinical photographs. In conclusion, this technique offers a mechanism for generating anonymized catalogued radiology museums in PACS. Museum Builder represents a working prototype that demonstrates some of the archiving functions that are expected by teaching institutions from PACS.
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Introduction
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The radiology museum is an integral component of every radiological training scheme. Over the past 5 years, the practice of radiology has moved from film to PACS, but the ability to build radiology museums has not kept pace [1].
For many of us, the hardcopy ACR collection provided hours of study and exam practice material. Those cases we saw in our formative years of radiological training often become "index" cases against which those that followed were measured. These museums, which are becoming increasingly obsolete [2], often comprised cupboard-like rooms filled with shelf upon shelf of ageing radiographs in various states of disorganization. Radiological museums have now diversified into multiple digital formats. DICOM files can easily be converted and saved in a number of manageable formats [3]. Large institutional collections can be acquired on CD-ROM [4, 5]. Personal teaching collections can be created in any number of readily available image databases [6–10]. Some of these databases are specifically designed for archiving radiological teaching cases and sometimes for storage on servers [4, 11, 12] for sharing access across networks or the World Wide Web [13]. Online database applications allow free text searches across thousands of cases, sometimes in multiple institutions [13]. These archives are used for research, teaching [2, 9, 10, 14] and for assessment of radiological expertise [15]. With this digital diversity has come a subtle change in the look and feel of the radiology museum. Hardcopy museum cases must be read in the same way that hardcopy radiology is practiced; with a light box. Digital museum cases are read from personal computers and not in the PACS environment in which many of us now work. One of the obstacles to replicating the PACS environment on a PC is the prohibitive size of the DICOM files. A solution to these problems is not to replicate PACS in order to build a work-like radiology museum, but to build a radiology museum within PACS. To the best of our knowledge, the major PACS manufacturers provide only limited tools for archiving radiology teaching cases, whereas most radiologists consider this sort of functionality important or even essential when considering the purchase of PACS [16]. Some provide a system of academic folders that require a system administrator to set up. These provide inadequate archiving and retrieval mechanisms for generating usable databases within PACS [1]. Neither does there appear to be any third party solutions that meet these criteria. PACS manufacturers prohibit access to their databases other than by their employees and, therefore, a novel approach is required for third parties to generate teaching cases on PACS. The aim of this study was to see if it was feasible to develop a software application that could edit the DICOM headers to anonymize and catalogue teaching cases in order to build a radiology museum within PACS.
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Materials and methods
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Principle
Radiological studies stored on PACS can be identified and retrieved using a number of search fields common to all PACS – namely, the patient's surname, forename, middle names and unique hospital number. This information is stored within a header in every DICOM file (Figure 1
). This usually means that every image, in every series, in every radiological study contains this information embedded within it. Multiframe images, generated with ultrasound, contain the same information in a single header. Both of these types of DICOM file can be handled in the same way. After DICOM data has been generated by a radiological investigation, it is pushed to the PACS server to be archived. As PACS receives the DICOM data, it reads the DICOM header and stores the patient specific data in a database. When PACS is queried to search for a particular patient, it is this database that is searched and not the DICOM archive itself. This entry in the database, however, points to the DICOM dataset within the archive, which can then be retrieved and opened. Our application, called Museum Builder, exploits this process by replacing the patient specific data within the header of DICOM files that have been exported from PACS. When the DICOM files are returned to PACS, the new information within the header is added to the PACS database as a "new" patient. The DICOM files for the museum case are effectively duplicated, but with a new DICOM header. In effect, PACS sees Museum Builder as any other radiological modality contributing to the local PACS archive.
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Figure 1. A screenshot of a readout from a hexadecimal editor of the header from a DICOM file demonstrating the ASCII values of the binary data. The patient specific binary data can be identified and edited with Museum Builder.
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Hardware and software
Our institution is a film-free hospital with a GE Centricity PACS (General Electric, Milwaukee, WI). Images can be viewed from a mixture of dedicated reporting workstations and PC-based web-browsers, which cover the whole hospital on a network with a 2 Gb s–1 backbone and a 100 Mb s–1 link to workstations. Museum Builder was developed using .NET technology and C# as the preferred language (Microsoft .Net Framework to run and Visual Studio to compile the C# source code). Museum Builder was installed on a networked PC (Pentium 4 CPU 2.80 Ghz with 1.0 Gb of RAM running Microsoft Windows XP Professional, version 2002, with Service Pack 1). An academic licensed version of eFilm Workstation 1.9.4 [17] was installed as the helper application.
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Results
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Process
Museum Builder can work with most PC based DICOM browsers, which for the purpose of this article will be referred to as the helper application. After opening Museum Builder, the helper application's database can be browsed or searched using search fields for the patient's name or hospital number. Cases are then identified for museum archiving and highlighted. Once selected, the patient's surname, forename, hospital number and date of birth are displayed in a row of text fields. Below this a second row contains the text fields for the anonymized museum case. The patient's "new" surname and forename are selected from pre-defined menus. Optional middle names can also be entered. The new hospital number comprises a three letter code, again selected from a menu, followed by a unique four digit number generated by Museum Builder (Figure 2). The drop-down menu selections can be over-ridden by entering text into the fields manually. The patient's date of birth is automatically anonymized to 1 January of the year of their birth, thus preserving age-related information in the DICOM header. Once the minimum number of fields has been completed (surname, forename and hospital number), the case is ready for anonymization (Figure 2). Clicking the "anonymize" button will then replace the patient specific data in each header of each DICOM file within each directory of the chosen radiological study or studies and the helper application database is modified accordingly. All other identifiable labels, private or otherwise, are changed or erased. This one click anonymizes every radiological study in the eFilm database for that patient; there is no limit to the number of types of examination, e.g. conventional radiography, CT, ultrasound or MRI, that can be processed at once. Even for large datasets with multiple examinations this only takes a few seconds on the workstation described. The process is simple and is currently performed in our department by clerical staff. Every DICOM file generated by a medical imaging device contains a unique identifier (the study SOP instance UID). At this stage, Museum Builder assigns each new case with a new unique identifier, generated internally from a sub-delegate range offered by Medical Connections [18], so that PACS does not recognize it when it returns. PACS just sees another new case arriving from a medical imaging device. When coding and anonymization is complete, Museum Builder composes an HL7 Radiology order message, which is sent to the PACS HIS/RIS broker. On receipt of this acknowledgment the new museum case is pushed from the helper application back to PACS (Figure 3).
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Figure 2. A screenshot from Museum Builder's anonymization window. The patient specific fields are replaced by catalogue headings that are selected from drop down menus.
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Figure 3. A schematic diagram demonstrating data flow between Museum Builder, the helper application, PACS and RIS/HIS.
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Catalogue headings
The American College of Radiologists (ACR) has established a well-recognized classification system for radiology [19]. This system allows high-level discrimination of radiological diagnoses, and therefore accurate retrieval of data, particularly for research. However, the system is not entirely intuitive, and therefore a different classification system has been used in Museum Builder. The catalogue headings are almost universal within radiology. The patient's surname is changed to a radiological anatomical unit, which broadly defines the sections of the human body that radiological investigations cover. These consist of head, neck, chest, abdomen, pelvis, extremities and breast. The patient's forename is selected from a surgical sieve consisting of normal, developmental, trauma, infection, neoplasia, inflammation, vascular, metabolic. Thereafter there is an option to add one, two or more middle names from a selection of organ specific titles such as liver, lung, brain, adrenal and so on. The hospital number is replaced by a unique museum number that comprises a three-letter code followed by a four-digit number. The code reflects subspecialty interests within radiology and include MSK for musculoskeletal, GIT for gastrointestinal and H&N for head and neck (Figure 2
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Non-radiological images
Many DICOM browsers will import non-DICOM image files such as JPEG and TIFF files. During the import process, DICOM header fields are entered manually and new DICOM files are generated. This allows non-radiological images to be added to the museum case, including histology, arthroscopy, endoscopy and clinical photographs (Figure 4). The report field of these "new studies" can then contain pathology reports, operative notes and clinical findings.
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Figure 4. A montage of screenshots demonstrating material from a single museum case including computed radiography, MRI, arthroscopy and histology.
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Reports
Reports for the museum cases can be added to the PACS RIS. These can be added by pasting text into a report window in Museum Builder (Figure 5). These reports can include copies of the original radiological report or can be entirely new and contain clinical histories, updated radiological reports, results of other special investigations, differential diagnoses and discussion.
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Figure 5. A screenshot demonstrating the"Report Window" where the text of the museum case has been pasted in prior to sending to RIS in an HL7 script.
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Discussion
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Museum Builder is a fully working prototype that has some of the functionality required by teaching institutions to develop radiology museums within PACS. It uses a novel approach to generating anonymized searchable teaching cases without accessing the PACS database directly. Teaching cases can then be read in the PACS environment in which the radiology trainee and his or her trainers work. Instead of being presented with single or selected digital images from a teaching archive or CD-ROM, the trainee has access to the whole DICOM dataset. When reading cross-sectional investigations, the trainee would have to interrogate the entire dataset, including localizers and sequences repeated because of technical problems, to gather the signs necessary to yield a diagnosis. It is this process that cannot be replicated by non-DICOM museums and teaching collections.
There are limitations to radiological museums created by Museum Builder. There is no free-text search function within the PACS browser window, which would allow the user to search for a specific diagnosis. However, the objective was to create a radiological museum that functioned in a similar manner to the ACR hard copy museum and therefore did not require the ability to immediately recall specific cases. Trainees can search through the database through catalogue headings based on anatomical site, disease process and radiology subspecialty.
Museum Builder can be used with any PACS and, in theory, integrated with any PACS broker, but this has only been tested with PACS in our institution. Whilst it should work with any PACS broker, the concept of Museum Builder does not allow for a "plug and play" solution. Museum Builder needs to be configured for each PACS broker in the same way that any CT or ultrasound machine must be configured to work with a particular PACS. However, configuring Museum Builder has been simplified by using variables in the HL7 code that can be defined from within the Access database according to the local PACS broker profiles.
The concept of Museum Builder is relatively simple and the coding is mainstream. It currently works as a bolt-on application to PC-based DICOM browsers, but there are a number of options for further development. Museum Builder could be coded to work as a DICOM client and, therefore, could stand alone in its integration with PACS and RIS. However, it does not make sense to repeat the work done by many affordable or free, readily available proprietary DICOM browsers. It would be easier to add Museum Builder's functionality to these applications. The most elegant solution would be for the PACS manufacturers to add this functionality to their current systems. That way the radiologist could build his or her DICOM radiology museum without leaving PACS.
This sort of functionality within PACS has certain implications for governance of the educational material because other allied healthcare workers outside radiology, and IT personnel, also have access to the database. In our institution we developed a governance protocol that was approved by the Caldicott Guardian to ensure that the limitations of patients' consent to procedures and investigations were adhered to. Rather than being a risk, the radiology museum is considered a valuable hospital-wide resource. Generating validated case material is always time consuming, and therefore the number of museum cases has, so far, made a negligible impact on the PACS archive capacity. In theory, however, duplicating large volumes of archive material could have serious implications for storage and therefore needs to be carefully controlled. In our institution, all museum material must be approved by a Radiology Museum Committee, which acts as a gatekeeper safeguarding the quality of the PACS museum and controlling its impact on the clinical archive.
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Conclusion
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Museum Builder demonstrates that it is feasible to build anonymized catalogued radiology museums within PACS, by editing the patient specific headers within the DICOM files, and therefore without directly accessing the PACS database. Teaching cases generated with this tool allow the trainee to read the full DICOM datasets within the normal PACS working environment. By using PACS as the radiology museum repository, the problems of storing and transmitting large image files and directories can be overcome. Museum Builder provides a model for the some of functionality that many academic institutions would like to see added to PACS by the PACS manufacturers.
This projected was supported by a Kodak Radiology Fund Scholarship awarded by the Royal College of Radiologists in 2003.
Received for publication June 22, 2005.
Revision received December 6, 2005.
Accepted for publication December 9, 2005.
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Top
Abstract
Introduction
