Steven L. Fritz

Implementing a DICOM-HL7 interface application

The DICOM standard, in addition to resolving certain problems with the ACR-NEMA 2.0 standard regarding network support and the clinical data dictionary, added new capabilities, in the form of study content notification and patient, study and results management services, intended to assist in interfacing between PACS and HIS or RIS systems. We have defined and implemented a mechanism that allows a DICOM application entity (AE) to interrogate an HL7 based RIS using DICOM services. The implementation involved development of a DICOM- HL7 gateway which converted between DICOM and HL7 messages to achieve the desired retrieval capability. This mechanism, based on the DICOM query/retrieve service, was used to interface a DeJarnette Research film digitizer to an IDXrad RIS at the University of Maryland Medical Systems hospital in Baltimore, Maryland. A C++ class library was developed for both DICOM and HL7 massaging, with several constructors used to convert between the two standards.

Design requirements for DICOM patient, study, and results management

The DICOM services for patient, study and results management are recent additions to the ACR-NEMA standard. Commercially available RIS systems and the HL7 standard do not match the DICOM state transition models for these management tasks well. The purpose of this effect is to model the interaction between a DICOM-compliant PACS and an RIS, based on the DICOM management models, to provide a basis for standards-based PACS-RIS integration. We report on a state transition model for a RIS that correlates both to the HL7 trigger events usually supported and to the major features of the various state transition models incorporated in DICOM.

Reference architecture for DICOM-compliant PACS development

DICOM semantics refers to the specification of meaning of DICOM messages exchanged between two DICOM-compliant systems. DICOM-compliant PACS networks may fail to achieve interoperability due to different variations in allowable DICOM semantics used by different implementors. We have specified the beginnings of a DICOM reference architecture by designing a generic PACS network, selecting certain PACS functions commonly implemented in DICOM application entities and making explicit assignments of various DICOM service classes to carry out the selected application level functionality. A generic PACS based on the reference architecture presented here is being implemented with the intention off providing Internet access to it for interoperability testing.

Object-oriented ACR-NEMA data dictionary in C++

The ACR-NEMA 2.0 standard has made important strides toward providing a manufacturer- independent interconnection for PACS systems. The DICOM standard now in preparation takes an object-oriented approach to design of software protocols for data base query and image exchange. We have developed an object-oriented class library for accessing an ACR- NEMA 2.0 data dictionary and building ACR-NEMA formatted messages. The library, implemented in both Smalltalk/V and being implemented in C++, provides access to the entire ACR-NEMA 2.0 Data Dictionary and allows a program written in either language to ascertain required fields in messages, default values and allowable values of enumerated value elements. The design of the class hierarchies in the data dictionary is discussed in terms of the ACR-NEMA 2.0 standard and the integration of this design into the DICOM standard. Building a sample SEND_REQUEST message for image transfer is illustrated.

Scanned Projection Radiography Using A Time-Delay-And-Integrate Scanning CCD

A scanned projection radiography sensor has been developed using a time-delay-and-integrate imaging CCD optically coupled to an X-ray intensifying screen. A mathematical model has been developed to predict the efficiency of information transfer between intensifying screen and CCD. This model predicts that for an 8-inch field of view the CCD should capture one electron for each X-ray photon absorbed in the screen. Variance in the number of electrons captured should reduce the DQE of the screen by a factor of 0.7. This almost exactly offsets the effect of scattered radiation in film/screen systems, suggesting that the new detector could have image quality equivalent to a screen/film/grid system. Experimental data shows that the model correctly predicts the light photon transfer efficiency of the system but that the image noise is dominated by switching noise from the CCD. With a low-noise camera design the system should be equal or superior to a screen/film/grid system for a wide range of practical imaging situations.

Community archiving of imaging studies

The quantity of image data created in a large radiology practice has long been a challenge for available archiving technology. Traditional methods ofarchiving the large quantity of films generated in radiology have relied on warehousing in remote sites, with courier delivery of film files for historical comparisons. A digital community archive, accessible via a wide area network, represents a feasible solution to the problem of archiving digital images from a busy practice. In addition, it affords a physician caring for a patient access to imaging studies performed at a variety ofhealthcare institutions without the need to repeat studies. Security problems include both network security issues in the WAN environment and access control for patient, physician and imaging center. The key obstacle to developing a community archive is currently political. Reluctance to participate in a community archive can be reduced by appropriate design of the access mechanisms.

C++ class library for DICOM services to support a HIS/RIS interface

The DICOM standard for medical image management was developed primarily based on a model of image transfer between image management systems, especially imaging modalities. The HL7 standard has developed for generic electronic information exchange in a healthcare environment. We have developed a C++ class library to support both DICOM and HL7 v 2.0 network environments and allow for interaction between DICOM image management systems and HL7-based radiology information systems. The class library includes basic classes for DICOM information objects and HL7 messages and message segments. In addition, it defines mutual constructors which can build objects for one environment using objects from the other environment as input parameters. A subset of the class library was implemented to build a DICOM HL7 gateway described elsewhere in this Proceedings. This project demonstrated that the two standards have limited areas of incompatibility which do not prevent development of functioning interface gateways.

Distortion in the MRI Stereotactic Planning of Gamma Knife Radiosurgery

In stereotactic localization using MRI, distortion of the image is a main factor contributing to errors of measurement. Although correction algorithms for distortion due to magnetic field incongruities are well known, there may still be residual distortion in the image after application of these corrections. As such, a linear scaling of the MR image may have to be applied before localization. In this study, axial and coronal MR images from Gamma Knife radiosurgery treatments were analyzed for the amount and possible effect of this residual distortion. It was found that there was measurable distortion in the images, and that the pattern of distortion suggested that the scaling factors were significantly different along the two axes in each imaging plane. The pixel sizes in the axial plane were 1.17 mm (.0044) along the Y-axis and 1.19 mm (.0038) along the X-axis. The pixel sizes in the coronal plane were 1.20 mm (.0055) along the Z-axis and 1.16 mm (.0031) along the X-axis. It was concluded that in order to reduce errors in localization, linear scaling factors must be applied in each imaging plane along each axis for every patient.

Low-frame-rate pulsed fluoroscopy vs low-exposure-rate continuous fluoroscopy: a comparison

Although improved video camera sensitivity has been responsible for reducing the radiation exposure rate in conventional fluoroscopy substantially over the last two decades, considerable further improvement is possible. Over the same period two methods for reducing fluoroscopic exposure have been implemented by various researchers: pulsed X-ray irradiation and progressive video acquisition of the image intensifier output at low frame rate with exposure per frame comparable to conventional fluoroscopy; and continuous irradiation with a combination of low exposure rate, high detector gain and X-ray beam filtration. Neither has come into widespread clinical use. This paper proposes a model of fluoroscopic patient exposure and compares pulsed fluoroscopy with other methods of exposure reduction. The implications of this model for fluoroscopic exposure rate optimization are discussed.

ACR-NEMA 2.0-based teleradiology system

Existing teleradiology systems rely almost exclusively on frame-grabbed images from a video source to input data from a variety of modalities. This report details implementation of a teleradiology system which uses an ACR-NEMA gateway to access imagery from a variety of modalities with the full dynamic range of the original data. Such a system allows the user to use the full capability of window and level control to adjust the gray level of the resulting display. The penalty is that since most teleradiology systems transfer 8-bit data and most existing ACR-NEMA modalities transfer 12-bit data in a 16-bit pixel format, transmission times are potentially longer. This may be addressed to some extent with more sophisticated data compression. Ultimately the availability of faster telecommunications services to remote locations such as a radiologists home will provide a better solution.