In this chapter, we have briefly reviewed the techniques of in vivo NMR spectroscopy and chemical shift imaging. These techniques are complementary, and both are of great potential clinical significance. Most of the data presented here is limited to 31P and 1H NMR, but with additional refinements, 13C and 19F NMR will likely be studied in the near future.
After a few years of the use of clinically oriented imaging, magnetic resonance (MR) can now be measured against the other cross-sectional radiologic imaging techniques. Its superior sensitivity in demonstrating diseases of the central nervous system and heart has yet to be matched by similar success in the detection of abdominal disease. However, MR is evolving further and improvements in hardware, software, and pulse sequence selection are expected to continue. We present here the experience accumulated to date in the MR evaluation of the kidney in its normal and diseased states.
To determine the accuracy of left ventricular ejection fractions (EFs) calculated from magnetic resonance (MR) images, 22 patients who underwent coronary angiography and left ventriculography were studied within 1-3 days by MR imaging. ECG-gated spin-echo 30-msec echo-delay images were obtained in end systole and end diastole in a plane through the long axis of the left ventricle perpendicular to the septum at a level through the aortic valve and apex. The area-length method was then used to calculate the EF from left ventriculograms and MR images.
Forty-three patients with liver metastases were imaged using 14 different pulse sequences (average, 7.5 sequences per patient) to allow direct comparison of their performance. "T2-weighted" spin-echo (SE) images, "T1-weighted" inversion recovery (IR) images, and "T1-weighted" SE images were obtained using a wide range of timing parameters. Pulse sequence performance was quantitated by measuring liver signal-to-noise (S/N) ratios and cancer-liver signal difference-to-noise (SD/N) ratios. Data were standardized to reflect a constant imaging time of 9 minutes for all pulse sequences.
We report the first clinical experience with a new method for projective imaging of blood vessels (angiography) using magnetic resonance. Vascular contrast is produced noninvasively by the phase response of moving protons. Diastolic and systolic gated images produce, respectively, flow signal and flow void; the difference image is a map of the pulsatile flow: an arteriogram.
Magnetic resonance (MR) imaging allows freedom in choosing oblique planes of section and rotation of the image plane with respect to the frequency-encoded (F) and phase-encoded (P) dimensions. A general method is described for understanding geometric relationships between the fixed magnetic coordinate system, patient positioning, and the flexible observer's coordinate system. Oblique planes of section are clinically useful in studying organs with an axis of symmetry that is oblique to the magnet coordinate system, such as the heart.
Bovine immunoglobulins (IgG) and bovine serum albumin (BSA) were multiply labeled with multidentate ligands, either ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA), and metal ions were inserted to form the ternary protein-ligand-ion conjugates. The NMRD profiles (the magnetic field dependence of 1/T1) of solutions of the ternary conjugates differ greatly from those of the corresponding binary ligand-metal-ion complexes, both in magnitude and functional form, exhibiting 5- to 10-fold greater relaxivities and prominent peaks near 20 MHz.
Using a modification of the partial saturation (PS) pulse sequence, we developed an MR method that permits the acquisition of highly T1- and T2-weighted images of the head and body in as little as 10 sec. The PS images, which were acquired at 0.6 T in a series of six patients with acute and subacute hemorrhage, showed a striking reduction in the signal intensity of hemorrhagic lesions. This effect, which is related to bulk magnetic susceptibility variations, was either minimal or absent on conventional T1- and T2-weighted spin-echo (SE) images.
The authors demonstrate that it is possible to obtain highly T1-weighted images of the abdomen using a suspended respiration partial saturation (SRPS) method in a breath-holding interval. T2*-weighted images, which reflect tissue T2 as well as variations in the static magnetic field, can also be rapidly obtained. The authors studied five healthy subjects and 19 patients with a variety of liver abnormalities, including benign and malignant hepatic neoplasms, fatty liver infiltration, ascites, and hematoma.
Intravascular signal from flowing blood is frequently observed on magnetic resonance (MR) images and may be indistinguishable from partial or complete vascular occlusion caused by thrombus or tumor. With a phase-display reconstruction method, qualitative assessment of large-vessel patency within the abdomen was undertaken in 15 healthy subjects and 12 patients with angiographically or surgically documented intravascular thrombus or tumor. Computed tomographic (CT) scans were available in all patients for correlation.
