ABSTRACT
The proton T(1) was measured at 132 µT in ex vivo prostate tissue specimens from radical prostatectomies of 35 patients with prostate cancer. Each patient provided two specimens. The NMR and MRI measurements involved proton repolarization, a field of typically 150 mT and detection of the 5.6-kHz signal with a superconducting quantum interference device. Values of T(1) varied from 41 to 86 ms. Subsequently, the percentages of tissue types were determined histologically. The theoretical image contrast is quantified for each case by δ = [1 - T(1) (more cancer)/T(1) (less cancer)]. A linear fit of δ versus difference in percentage cancer yields T(1) (100% cancer)/T(1) (0% cancer) = 0.70 ± 0.05 with correlation coefficient R(2) = 0.30. Two-dimensional T(1) maps for four specimens demonstrate variation within a single specimen. These results suggest that MR images with T(1) contrast established at ultra-low fields may discriminate prostate cancer from normal prostate tissue in vivo without a contrast agent.
Subject(s)
Magnetic Resonance Imaging/methods , Magnetic Resonance Spectroscopy/methods , Prostatic Neoplasms/pathology , Diagnosis, Differential , Humans , Image Enhancement/methods , In Vitro Techniques , Linear Models , Male , Neoplasm Grading , ProstatectomyABSTRACT
MRI is a powerful technique for clinical diagnosis and materials characterization. Images are acquired in a homogeneous static magnetic field much higher than the fields generated across the field of view by the spatially encoding field gradients. Without such a high field, the concomitant components of the field gradient dictated by Maxwell's equations lead to severe distortions that make imaging impossible with conventional MRI encoding. In this paper, we present a distortion-free image of a phantom acquired with a fundamentally different methodology in which the applied static field approaches zero. Our technique involves encoding with pulses of uniform and gradient field, and acquiring the magnetic field signals with a SQUID. The method can be extended to weak ambient fields, potentially enabling imaging in the Earth's field without cancellation coils or shielding. Other potential applications include quantum information processing and fundamental studies of long-range ferromagnetic interactions.
Subject(s)
Algorithms , Image Enhancement/methods , Image Interpretation, Computer-Assisted/methods , Imaging, Three-Dimensional/methods , Magnetic Resonance Imaging/methods , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
We obtained nuclear magnetic resonance (NMR) spectra of liquids in fields of a few microtesla, using prepolarization in fields of a few millitesla and detection with a dc superconducting quantum interference device (SQUID). Because the sensitivity of the SQUID is frequency independent, we enhanced both signal-to-noise ratio and spectral resolution by detecting the NMR signal in extremely low magnetic fields, where the NMR lines become very narrow even for grossly inhomogeneous measurement fields. In the absence of chemical shifts, proton-phosphorous scalar (J) couplings have been detected, indicating the presence of specific covalent bonds. This observation opens the possibility for "pure J spectroscopy" as a diagnostic tool for the detection of molecules in low magnetic fields.
