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J J Ford

Publications and source records attributed to J J Ford.

142 records · Page 8Linked to original sources
PubMedDate not supplied

Change in red blood cell relaxation with hydration: application to MR imaging of hemorrhage.

T1 and T2 were measured in unclotted blood samples with 0.24- and 4.7-T spectrometers. The fraction by weight of intracellular water in the red blood cells (RBCs) was varied by either osmotic manipulation or density separation in concentrated (packed RBCs) and dilute (RBCs suspended in buffer or serum) samples. Reducing the cell water content caused a moderate decrease in T1 and a profound decrease in T2 at both 0.24 and 4.7 T. Conversely, increasing the cell water content caused an increase in both T1 and T2. The authors conclude that dehydrated RBCs in an area of hemorrhage would cause a substantial decrease in signal intensity on long TR/TE (T2-weighted) images. Overhydration of RBCs would have the opposite effect.

Adult↗
PubMedDate not supplied

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 T1's 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.

Humans↗
PubMedDate not supplied

Mechanisms of MR signal alteration by acute intracerebral blood: old concepts and new theories.

We reviewed the current literature and theories pertaining to the appearance of hemorrhage on MR images. New theories were formulated to explain the etiology of spin-echo (SE) and gradient-echo contrast on clinical MR images of hematomas at low and intermediate field strengths. It is our hope that these theories will prompt further experiments to prove or disprove their validity. The discussion of SE contrast focuses on the powerful MR effects mediated by changes in protein concentration. These changes are postulated to occur as a result of (1) clot matrix formation; (2) settling of RBCs, which increases the number of RBCs per unit volume and the total protein concentration; and (3) alterations in intracellular protein concentration caused by changes in RBC hydration. The contribution of acid methemoglobin to image contrast via the proton electron dipole-dipole mechanism is also included. The discussion of gradient-echo contrast focuses on the inhomogeneity that may be present within voxels that contain a blood clot. This inhomogeneity results when the voxel contains regions with different magnetic susceptibilities (i.e., clumped RBCs and serum). Two temporally arranged schemata for T2-weighted and T1-weighted SE scans are presented that illustrate how these factors might interact to explain the diverse appearance of hematomas on clinical SE images. The signal intensity on T2-weighted SE scans appears to be dependent primarily on the state of hydration of the RBC. This factor and the presence or absence of methemoglobin appear to be the major factors that govern contrast on T1-weighted SE images.

Acute Disease↗
PubMedDate not supplied

Effect of clot formation and retraction on spin-echo MR images of blood: an in vitro study.

Phantoms were constructed that contained red blood cell (RBC)-free clots in varying stages of clot retraction. MR images of these samples were compared with those of retracted whole venous blood clots and a fresh rat brain standard. Images were obtained at 0.3 T, 0.5 T, 1.0 T, 1.5 T, and 2.4 T with T1-, spin-density- and T2-weighted spin-echo pulse sequences. The presence or absence of venous blood cells in the clot caused only minor differences in T2- and spin-density-weighted images of the clots at or below 1.5 T. On T2-weighted scans, the retraction of the RBC-free clot resulted in a progressive decrease in signal intensity at 2.4 T. Fully retracted RBC-free clots were markedly hypointense relative to serum and ranged from slightly hyperintense to isointense with brain and venous clots at 0.5-1.5 T. There were no striking concomitant signal intensity changes on the spin-density- or T1-weighted scans, which could have caused the changes seen on the T2-weighted images of the clots. Our results indicate that the physical basis of these MR effects in the RBC-free clots is the concentration of plasma protein. The combined concentration of plasma protein and the tightly packed RBC proteins in the venous clots causes the strikingly similar MR appearance of venous and RBC-free clots on clinical images. These results do not demonstrate the presence of the previously postulated selective T2 relaxation of intracellular paramagnetic deoxyhemoglobin in these in vitro venous clots.

Animals↗
PubMedDate not supplied

Magnetic resonance imaging in multiple sclerosis: results in 32 cases.

A prospective clinical study was performed in 32 patients with multiple sclerosis (MS) to evaluate the sensitivity of lesion detection and accuracy of lesion localization by neurologic examination, delayed enhanced computed tomography (CT) with a double dose of contrast material, and proton magnetic resonance (MR) imaging. After neurologic examination patients were classified by probability of MS (possible, four patients; probable, three patients; and definite, 25 patients) and by disease activity (acute, chronic with acute exacerbation, or chronic progressive). Subsequently they underwent delayed enhanced CT scanning and MR imaging with more than one spin-echo technique. In five of seven patients with possible or probable MS, both MR imaging and delayed enhanced CT were negative. In 25 cases of definite MS, MR imaging detected pathology in 19 (76%) cases, while CT detected lesions in 15 (60%) of 25 cases. In acute lesions (acute or chronic with acute exacerbation), the two techniques were of similar sensitivity (delayed CT was positive in 65% and MR imaging in 60%), while in chronic progressive MS, MR imaging was superior in lesion detection (MR imaging positive in 75%; delayed CT in 25%). While most lesions (55%) were seen in corresponding locations in both studies, neither MR nor delayed CT correlated well with lesion localization by neurologic examination because a large number of asymptomatic lesions were imaged and many symptomatic lesions were undetected.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

MR appearance of extravasated gadolinium contrast medium.

This case illustrates that a large zone of signal void can be produced on short relaxation time MR images when gadopentate dimeglumine is injected through an infiltrated intravenous catheter. The authors consider the physics behind this paradoxical decrease in signal intensity where there are high concentrations of gadopentate dimeglumine.

Contrast Media↗
PubMedDate not supplied

Testicular composition, number of A spermatogonia, germ cell ratios, and number of spermatids in three different breeds of boars.

Seminal quality, including the number of spermatozoa in the ejaculate, varies among breeds of boars. Variation in seminal quality may be explained by breed differences in testicular size and composition. The objective of this study was to characterize testicular composition and population sizes of germ cells and somatic cells in three different breeds of boars. Testes from mature and normal Meishan (M, n = 5; age 225 days), Whitecross (WC, n = 5; age 346 days), and West African (WA, n = 5; age 322 days) boars were either fixed in Zenker-formol or perfused with glutaraldehyde, embedded in Epon, sectioned at 0.5 microns or 20 microns and evaluated stereologically for germ cells, Leydig cells, Sertoli cells, and other testicular structures. The paired parenchymal weight was higher (P < 0.05) in the WC (498 +/- 35 g) than in the M (247 +/- 17 g) or WA (133 +/- 10 g). The nuclear volumes per boar of Sertoli cells, type A spermatogonia, leptotene, zygotene, pachytene, secondary spermatocytes, spermatids with spherical nuclei, and spermatids with elongated nuclei were higher (P < 0.05) in the WC than in the M or WA. The nuclear volumes per boar of blood vessels and Leydig cells were exceptionally higher (P < 0.05) in the M than in the WC or WA. The average germ cell nuclear diameters were similar (P > 0.05) for the M and WC but least (P < 0.05) in the WA breed. Also, the nuclear diameters of Leydig cells and Sertoli cells were higher (P < 0.05) in the M than in the WC or WA. The population sizes of all the intratubular components were positively correlated (P < 0.05) with testicular size (weight). Volume density of seminiferous tubules was similar in the WA and WC, but was lowest in the M, who had the highest density of Leydig cells. However, due to the larger testes, all germ cell types and Sertoli cells were higher in the WC than in the WA or M. The M and WA had similar low numbers of type A spermatogonia, but there was less term cell degeneration in M than in Wa, such that M spermatids were intermediate in number between WA and WC.

Animals↗