Development of the scintillation camera.

It is clear that, aside from the tremendous development in radionuclides and radiopharmaceuticals, the one thing that has had the largest impact on the practice of nuclear medicine has been the introduction of the stationary imaging device known for so long as the Anger Camera. It has evolved from a relatively simple system which many users could repair themselves, if the need arose, to an exceedingly complex and versatile tool of diagnostic medicine. As was stated in the introduction, the practice of modern day nuclear medicine without the scintillation camera is inconceivable.

Experience with gated cardiac software phantoms for quality control of applications programmes.

Ten gated cardiac software phantoms, representing normal and abnormal clinical conditions, were transferred to 9 different computer systems and tested with 11 cardiac programmes. Problems of inappropriate data format were encountered when analysing the phantoms on other systems. The global left ventricular ejection fraction (LVEF) values resulting from the different programmes were compared. Significant programme differences were found, the programmes falling generally into two groups. Few LVEF outlier values were identified. Full functional assessment of cardiac phantoms requires a set of different views which together form the phantom. Application of software phantoms for programme assessment and training requires prudence and attention to the acquired data format, frame time, and gating method for the appropriate use of phantoms.

The right-left symmetry axis of the brain on CT.

The location of the brain's symmetry axis on computerized tomography (CT) images was mathematically formulated. A series of computer programs were written to "peel off" the skull and artifacts external to the skull. Image lines were then tested for right-left symmetry and in each line a pixel was selected which best represented the center of symmetry of the skull contents. The resultant calculated symmetry line of images with and without pathology was comparable to the visually determined symmetry axis. This method permits computed screening for right-left asymmetry.

Digital image motion correction by spatial warp methods.

A technique for correction of motion between images which are obtained in high-speed digital subtraction or cine angiographic acquisitions is being tested. The method is based on the application of quadratic polynomial equations which transform one image so that it matches a reference image. Images which have been processed in this manner can be summed to improve the signal-to-noise ratios over individual images. The technique for motion correction currently being tested uses operator interaction to establish the appropriate polynomial transformation. An operator selects fiducial (reference) points on an image which will be the reference. Then he selects the corresponding fiducial points on the image to be processed. The algorithm calculates the coefficients of a pair of quadratic polynomial equations and applies them to each pixel in the image. Results demonstrate the application of the technique in phantoms and in digitized cine angiograms.

Medical image management: practical, legal and ethical considerations.

The data acquired by the new medical imaging techniques, in many ways, exceeded our ability to properly store, transmit and use the images produced. As diagnostic imaging procedures become progressively less invasive and traumatic, they are being applied to a much larger patient population. The decrease in memory and other instrumentation costs, along with expanded technological capability of computer systems, has provided medicine an opportunity to create network systems for the storage, processing, recall, and remote location of these diagnostic images. Therefore, problems of access and confidentiality have become increasingly important. This communication will consider certain medical, legal, and ethical aspects of these technologies of data acquisition, storage, manipulation and retrieval.

Work in progress: ultrasonic texture of normal rat liver tissue using a standardized in vivo measurement.

A prototype computer-augmented diagnostic ultrasound system was used in an investigation of the range of echo amplitudes obtained from measurements of normal exteriorized rat livers. A secondary goal was to develop a method for minimizing variations in measurement techniques and instrument stability. The average echo amplitude was obtained from a user-selected homogeneous region of the liver on a B-mode scan image. A similar B-mode scan of a commercially available liver tissue equivalent phantom was also obtained immediately after each rat liver measurement and was used as a calibration scan. A normalization factor developed from the calibration scan was used to correct all in vivo measurements for system variation. The average echo amplitude from the livers of a group of normal rats, when corrected by the calibration scan, exhibited a narrow range of values with a coefficient of variation of only 5%. The development of a technique that yields a narrow range of values for normal tissues should encourage further investigation of tissue characterization methods.

Simultaneous bi-plane digital video-fluoroscopy.

A prototype system for digital subtraction angiography that is capable of acquiring digitized video-fluoroscopic images simultaneously from both anterior and lateral imaging chains of a conventional bi-plane system was developed. A hardware module that takes images from both the anterior and lateral video cameras and displays them both on a single video image prior to digitization was designed and constructed. The three-dimensional information provided by a digital bi-plane images should improve the accuracy of cardiac-ventricular function studies. In addition, bi-plane imaging should reduce the need for additional views and the associated repeated injections of contrast media. With this technique, digital bi-plane imaging can be carried out with commercially available systems without duplication of the digital-processing chain.

The potential impact of digital radiography (DR) on the speciality of nuclear medicine.

Digital radiography is a reasonably economical system that helps diagnostic imaging physicians to develop increasingly less-invasive procedures, obtain maximal information at a given dose and increase the flexibility and convenience involved with diagnostic workups. The range of applications of DR has not been fully established at this time. Comparison of its properties with those of conventional nuclear medicine may suggest areas of potential application. Compared to nuclear medicine techniques, DR in general provides improved anatomical resolution, improved contrast resolution, sometimes equivalent functional information, and decreased imaging time. On the other hand, some functional nuclear medicine studies provide information not available by DR; including the gallium scan, bone scan, hepatic-biliary scan, and lung scan. Therefore, nuclear medicine procedures will be complimentary in some instances to digital radiography procedures and competitive in others. The proper roles of each modality in various clinical settings await future detailed and comprehensive efficacy studies.