John Hoenninger

Nuclear magnetic resonance imaging of mammary adenocarcinomas in the rat

A study of 24 rats implanted in the hind leg with mammary adenocarcinomas and five shamimplanted rats, followed from the second to the eighth week postimplantation, showed nuclear magnetic resonance imaging capable of detecting all the tumors without yielding any falsepositives in the control rats. The Tl relaxation time of tumors overlapped that of muscle, and the T2 times overlapped fat, but the combination was unique when comparing tumors to muscle and fat. Necrotic regions of the tumor and the bladder contents tended to have very long T1 and T2 relaxation times. The difference in relaxation time between tumors and muscle could be accounted for in terms of water content, which was approximately 8% higher for the tumors. The study corroborates data from previous studies indicating that NMR imaging is a highly sensitive modality, although T1 and T2 times are not exclusive indicators of malignancy.

Diagnostic Imaging—Magnetic Resonance Imaging

Publisher Summary This chapter discusses the development of magnetic resonance imaging (MRI) technology. MRI represents the leading edge of technology in the field of diagnostic imaging. MRI has achieved clinical significance and has become the primary modality in the investigation of head, spinal cord, pelvis, cancellous bone, pericardium, gall bladder, and lymph node masses and in the evaluation of joints. Hydrogen, which is available in high concentrations in the body, together with its associated magnetic properties, provides the key ingredient for the medical applications of MRI. The MRI requires the tissue being scanned to be exposed to three magnetic fields. The application of these fields, in coordination with the detected signals, is controlled by a computer. Powerful modern minicomputers, based on the latest very-large-scale integration (VLSI) technology, are required to handle the significant quantity of data that is generated and processed in the MRI systems. The unique approach to MRI system architecture is based on the identification of a number of tasks that can be performed in parallel. These tasks are very demanding when performed by a single computer but can be performed with a minimum of special hardware by an optimum combination of a microcomputer for control and a pair of minicomputers or super-microcomputers arranged in dual-computer architecture for data acquisition, image processing, display, and archiving.

Spatial Resolution in NMR Imaging

NMR imaging is used as an example of how spatial resolution can be improved in a signal-to-noise (S/N) limited situation. The NMR imaging process consists of two components-generating the NMR signal and localizing it in space. This paper will show that spatial resolution not only aids in identifying small structures, but improves the detectability of larger features by preserving their object contrast.

Designing Engineering Upgradability into Magnetic Resonance Imagers: Impact on Future Costs

MRI is a powerful diagnostic modality of expanding availability. Equipment and installation amount to nearly

Magnetic Resonance Imaging the Velocity Vector Components of Fluid Flow

2M per site. An important component of diagnostic efficacy is not just equipment costs but also replacement costs, which for x-ray CT amount to 14-20% of the purchase cost per year; and in the early years of that technology reached 30-50%. We show how design choices made during the R&D stages of MRI development have allowed us to improve system performance parameters such as data reconstruction, archiving and display speeds, computational capabilities, operator interfaces, imaging sequence flexibility and signal-to-noise levels. Over the last four years these improvements have been made at a retrofit cost well below our target of 6-7% of the purchase price per year.