Joseph J. Ford

Accurate T2 NMR images

We present a method for producing accurate calculated T2 nuclear magnetic resonance (NMR) images. A modified Carr-Purcell-Meiboom-Gill pulse sequence is used to obtain a series of images with progressive T2 dependence. This image series is then analyzed pixel by pixel to generate a T2 and initial signal strength image. Tests performed using four samples of known T2 indicate accuracies of better than 9%.

Relaxation times of normal and atrophied muscle

Magnetic resonance imaging is being used to investigate physiological changes induced by microgravity. Using human (bed rest) and animal (tail suspension) models simulating zero gravity, muscle atrophy was studied. Despite significant physiological changes in muscle mass, distribution of blood flow, and muscle water, no changes in muscle proton relaxation times were found at several different resonant frequencies (6, 10, 20, and 200 MHz). These results suggest that observed changes in relaxation times as reported in pathologic studies are likely due to the pathological changes and not the accompanying muscle atrophy.

Accurate T1 and spin density NMR images

We present a method for producing accurate calculated T1 and spin density nuclear magnetic resonance images. A modified Carr-Purcell-Meiboom-Gill pulse sequence is used to obtain a series of images containing both T1 and T2 dependence. The image series is first analyzed to remove the T2 dependence. The resulting images are then analyzed, pixel by pixel, to generate an image containing T1 values and an image containing values proportional to spin density (SD). Tests performed on two phantoms containing solutions of various known T1s and H2O/D2O concentrations indicate that the T1 image values are accurate to better than 11% and the relative SD values agree to within one standard deviation.

Improvements in the clinical utility of calculated T2 images of the human brain

Magnetic Resonance Imaging (MRI) affords a considerable improvement in image contrast over other methods by virtue of the intrinsic NMR parameters spin density, T1, and T2. However, the clinical utility of routine quantification of these parameters is currently unknown. Calculated T2 images might afford additional disease specific information provided the calculation algorithm generates accurate T2 values. In this study, calculated T2 images of a MnCl2 phantom (spanning a T2 range of interest of 45.7 ms to 346.6 ms at 6 MHz) were generated utilizing a variety of calculation algorithms based upon a data set of 32 sequential spin-echo (SE) images. In general, when utilizing only the earliest sequential SE after the 90 degree pulse for the T2 calculation, the greater the number of SE used in the calculation algorithm, regardless of how they were averaged, the more accurate and less noisy was the calculated image. When only limited numbers of SE were used in the calculation algorithm, accuracy and noise varied with the choice of TE suggesting that there may be optimal timings for TE for a particular T2 range of interest. Forty-two calculated T2 head images of normal subjects, based upon data sets of 16 sequential SE, were evaluated for the T2 values of normal brain. These were compared to T2 images calculated via 7 different algorithms based upon 16 SE data sets from two patients with CNS pathology. An optimal algorithm was identified in which 16 SE Carr-Purcell-Meiboom-Gill (CPMG) were averaged into two images for the T2 calculation. With this algorithm, calculated images could be generated efficiently which were accurate and relatively noise free. The availability of such images maximized whatever disease specificity, and thus clinical utility, T2 information affords.

Temporal changes in red blood cell hydration: application to MRI of hemorrhage

It has been established that red blood cell (RBC) dehydration causes significant changes in MRI signal intensity by decreasing both the T1 and T2 relaxation times. This study was conducted to determine if these changes occurred in blood clots maintained at body temperature for times ranging from 15 min to 10 days. Venous blood was used to form clots which were stored at 37°C. The shape and diameter of 20–50 RBCs were measured in the fresh and fixed states. By 12–48 h after clot formation virtually all RBCs lost their biconcave shape and became spherical echinocytes. The volume of these cells decreased by at least 15% over the next 72 h. This change indicates a decrease in the fraction of the cell weight occupied by water of 0.05, which is large enough to alter MR signal intensity significantly. The authors conclude that dehydration of RBCs occurs in vitro within an aging clot. If these changes occur in vivo they should cause a significant decrease in signal intensity on long TR/TE (T2-weighted) images.

Nuclear magnetic resonance diagnosis of an anaplastic astrocytoma

A patient presented with an 8-month history of a progressive left homonymous visual field deficit, left hemiparesis, and a left thalamocortical sensory deficit that was not detectable by repeated conventional neurodiagnostic evaluations. Proton nuclear magnetic resonance (NMR) imaging revealed a right parietal lesion characterized by a prolonged T2 (spin-spin relaxation time). At surgery, the mass proved to be an anaplastic astrocytoma. NMR appears to be more sensitive than x-ray computerized tomography scanning in some patients with malignant gliomas and offers the clinician an additional probe with which to evaluate these patients.