SEARCH · PubMed Health

Results for “Inversions”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources

PubMedDate not supplied

The substantia nigra in Parkinson disease: proton density-weighted spin-echo and fast short inversion time inversion-recovery MR findings.

BACKGROUND AND PURPOSE: A reduction in the area of the substantia nigra (SN) has been shown in patients with Parkinson disease. The substantia nigra is anteroinferolateral to the red nucleus, and it is important to precisely locate its true anatomic location to accurately measure SN area. Our purpose was to determine the exact location of the substantia nigra by correlating imaging and anatomic findings. We also attempted to quantitate SN area in patients with Parkinson disease compared with that in healthy control subjects on the basis of proton density-weighted spin-echo (SE) and fast short inversion time inversion-recovery (STIR) MR imaging findings. METHODS: In four healthy volunteers, dual-echo SE and fast STIR MR images were obtained in three orthogonal planes and an oblique coronal plane. These images were correlated with anatomic specimens to determine the location of the SN. The area of the SN was also measured on oblique coronal fast STIR images obtained at a plane perpendicular to the SN in 22 patients with Parkinson disease and in 22 age- and sex-matched healthy volunteers. RESULTS: The true anatomic location of the SN, anteroinferolateral to the red nucleus, was accurately identified, not on T2-weighted images, but on proton density-weighted SE images and fast STIR images as an area of hyperintense gray matter. The hypointense area seen on T2-weighted images corresponded to the anterosuperior aspect of the SN and to the adjacent crus cerebri. No statistically significant differences were noted in the size of the SN when the oblique coronal images of patients with Parkinson disease were compared with those of the control groups. CONCLUSION: The SN is located mainly beneath the red nucleus. Its location cannot be determined on the basis of T2-weighted imaging results but rather on the basis of proton density-weighted SE or fast STIR findings. SN volume loss is not found in Parkinson disease, and this finding is compatible with that of recent pathology reports in the literature.

Adult↗

PubMed2005

Phase shift due to inversion recovery process and chemical shift effect in inversion recovery prepared gradient-echo magnetic resonance imaging.

PURPOSE: The purpose of this study was to assess phase shift due to the inversion recovery process and the chemical shift effect in inversion recovery prepared gradient-echo magnetic resonance imaging. MATERIALS AND METHODS: The signal intensities of three phantoms, composed of physiologic saline solution with Gd-DTPA, olive oil, and fat emulsion, were measured on a 1.5 Tesla unit. The sequence was single-shot two-dimensional. The parameters were as follows: TI 100-2500 msec at 100 msec intervals, TR 11.25 msec, TE 2.250 msec, 3.375 msec, and 4.500 msec. The k-space was filled with the centric view order. RESULTS: The signal intensity curves of the emulsion showed various patterns. At a TE of 2.250 msec, TI at the minimum value of signal intensity was 1500 msec. At a TE of 4.500 msec, TI at the minimum value was 500 msec. Up to a TI of 1000 msec, the signal intensity at a TE of 2.250 msec was stronger than that at a TE of 4.500 msec, and from a TI of 1000 msec, the signal intensity at a TE of 4.500 msec was stronger than that at a TE of 2.250 msec. CONCLUSION: We concluded that fat emulsion showed paradoxical phase shift.

Contrast Media↗

PubMed1976

Familial pericentric inversion of chromosome 19, inv(19) (p13q13) with a note on genetic counseling of pericentric inversion carriers.

An inmate of a hospital for the mentally retarded was found during a cytogenetic screening programme to have karyotype 46,XY,inv(19)(p13q13)mat. Clinical, cytogenetic and family findings are presented and it is concluded that the chromosomes abnormality was probably not the cause of the patient's retardation. The problem of genetic counseling of inversion carriers is examined in some detail and estimates of risk are given.

Adolescent↗

PubMed1978

[Inversion polymorphism in the malarial mosquito, Anopheles messeae. III. The temporal dynamics of the inversion frequencies in the population of the center of a geographic range].

The karyotypic structure of the studied population shows the clear temporal differentiation. The frequencies of the homozygotes IIR/IIR, IIIR1/IIIR1 and IIIL/IIIL increase to the middle of the reproductive period. This homozygotes are initial gene arrangements in the phylogenetic sense and their adaptive value is evidently higher than the alternative homozygotes during the population flowering. Inter-year correlations of the dynamic frequencies of several gene arrangements appears to be due to density-dependent selection. The population karyotypic structure is characterised by a high dynamics during the season. However, no directional displacement of the inversion frequencies was observed. This stability is explained by homeostasis of the population genetic structure.

Animals↗

PubMed1995

The inverse problem of electrocardiology: the performance of inversion techniques as a function of patient anatomy.

Sixteen anatomically correct bodies have been studied to determine the performance of the inversion techniques of zero-order Tikhonov regularization and singular value decomposition. The bodies have varying heart height and diameter, thickness of subcutaneous fat layer, and distance of the heart from the left wall of the chest. Comparisons are made in terms of trade-off curves for noise amplification factor and spread of epicardial potentials. It was found that regularization performs better than singular value decomposition on all bodies; the larger the heart size, the more reliable the results; and for a given heart size, the thinner the subcutaneous fat layer, the more reliable the results. The distance of the heart from left wall of the chest was found to be a less significant factor for a given heart size.

Adipose Tissue↗

PubMed2006

Anatomy-based inverse optimization in high-dose-rate brachytherapy combined with hypofractionated external beam radiotherapy for localized prostate cancer: comparison of incidence of acute genitourinary toxicity between anatomy-based inverse optimization and geometric optimization.

PURPOSE: To evaluate the advantages of anatomy-based inverse optimization (IO) in planning high-dose-rate (HDR) brachytherapy. METHODS AND MATERIALS: A total of 114 patients who received HDR brachytherapy (9 Gy in two fractions) combined with hypofractionated external beam radiotherapy (EBRT) were analyzed. The dose distributions of HDR brachytherapy were optimized using geometric optimization (GO) in 70 patients and by anatomy-based IO in the remaining 44 patients. The correlation between the dose-volume histogram parameters, including the urethral dose and the incidence of acute genitourinary (GU) toxicity, was evaluated. RESULTS: The averaged values of the percentage of volume receiving 80-150% of the prescribed minimal peripheral dose (V(80)-V(150)) of the urethra generated by anatomy-based IO were significantly lower than the corresponding values generated by GO. Similarly, the averaged values of the minimal dose received by 5-50% of the target volume (D(5)-D(50)) obtained using anatomy-based IO were significantly lower than those obtained using GO. Regarding acute toxicity, Grade 2 or worse acute GU toxicity developed in 23% of all patients, but was significantly lower in patients for whom anatomy-based IO (16%) was used than in those for whom GO was used (37%), consistent with the reduced urethral dose (p <0.01). CONCLUSION: The results of this study suggest that anatomy-based IO is superior to GO for dose optimization in HDR brachytherapy for prostate cancer.

Aged↗

PubMedDate not supplied

Comparison of multishot echo-planar fluid-attenuated inversion-recovery imaging with fast spin-echo fluid-attenuated inversion-recovery and T2-weighted imaging in depiction of white matter lesions.

PURPOSE: To compare a multishot echo-planar fluid-attenuated inversion-recovery (EPI-FLAIR) sequence with fast spin-echo FLAIR (F-FLAIR) and fast spin-echo T2-weighted (FSE-T2W) sequences in depiction of white matter lesions. METHODS: Thirty-five patients with various white matter lesions were included in this prospective study. Two independent readers for lesion detection (lesion size, >2 mm) compared sequences quantitatively. In 22 patients, contrast was calculated between periventricular hyperintensity (PVH) and the cerebrospinal fluid (CSF). RESULTS: EPI-FLAIR revealed more lesions than FSE-T2W (p < 0.01). However, F-FLAIR revealed more lesions than EPI-FLAIR (p < 0.01). For PVH-to-CSF contrast, EPI-FLAIR demonstrated significantly higher contrast than FSE-T2W. There were no differences in PVH-to-CSF contrast between EPI-FLAIR and F-FLAIR. CONCLUSIONS: This study shows that EPI-FLAIR has distinct advantages over FSE-T2W in the depiction of white matter lesions. Although EPI-FLAIR reduces imaging time by more than 60% relative to F-FLAIR, it cannot replace F-FLAIR for the detection of lesions in the cerebral white matter.

Aged↗

PubMed1991

Generalizing Long's inversion of the matrix form of Prentice's equation and the concept of generalized inverse dioptric power.

The concept of generalized inverse dioptric power is introduced. Its use is illustrated in solving Long's matrix generalization of Prentice's equation for the decentration required to produce a specified prismatic effect. The solution holds in all cases for which a solution exists, including for the pure cylinder, and the result gives all solutions when more than one exists.

Eyeglasses↗

PubMed2002