Biomedical subjects

D Hearshen

Publications and source records attributed to D Hearshen.

4 recordsLinked to original sources

PubMed2001

Correlation between magnetic resonance spectroscopy imaging and image-guided biopsies: semiquantitative and qualitative histopathological analyses of patients with untreated glioma.

OBJECTIVE: Since intratumoral heterogeneity of gliomas is not adequately reflected in conventional magnetic resonance imaging (MRI), we sought to determine a correlation between different proton magnetic resonance spectroscopic imaging ((1)H MRSI) metabolic ratios and the degree of tumor infiltration in diffusely infiltrating gliomas. In this report, we describe the microscopic anatomy of gliomas on imaging. METHODS: Image-guided biopsies with semiquantitative and qualitative histopathological analyses from a series of 31 untreated patients with low- and high-grade gliomas were correlated with multivoxel (1)H MRSI referenced to the same spatial coordinates. RESULTS: This series yielded 247 tissue samples and 307 observations. Choline-containing compounds using contralateral creatine and choline for normalization or ipsilateral N-acetylaspartate appear to correlate best with the degree of tumor infiltration. Similar correlations were present within each grade after stratification. Despite the interpatient overlap of metabolic ratios between normal tissue and mild tumor infiltration, preliminary analyses revealed that (1)H MRSI appears more accurate than conventional MRI in defining the tumor boundary and quantifying the degree of tumor infiltration. CONCLUSION: This is the first study showing histopathological validation of tumor boundaries using (1)H MRSI. These results support the conclusion that (1)H MRSI accurately reflects the extent of the disease in patients with gliomas. This has important diagnostic and therapeutic implications for more accurately assessing the burden of disease as well as for planning and assessing response to therapy.

Adolescent↗

PubMed1998

Time course of ADCw changes in ischemic stroke: beyond the human eye!

BACKGROUND AND PURPOSE: Using newly developed computerized image analysis, we studied the heterogeneity of apparent diffusion coefficient of water (ADCw) values in human ischemic stroke within 10 hours of onset. METHODS: Echo-planar trace diffusion-weighted images from 9 patients with focal cortical ischemic stroke were obtained within 10 hours of symptom onset. An Iterative Self-Organizing Data Analysis (ISODATA) clustering algorithm was implemented to segment different tissue types with a series of DW images. ADCw maps were calculated from 4 DW images on a pixel-by-pixel basis. The segmented zones within the lesion were characterized as low, pseudonormal, or high, expressed as a ratio of the mean+/-SD of ADCw of contralateral noninvolved tissue. RESULTS: The average ADCW in the ischemic stroke region within 10 hours of onset was significantly depressed compared with homologous contralateral tissue (626.6+/-76.8 versus 842.9+/-60.4x10(-6) mm2/s; P<0.0001). Nevertheless, ISODATA segmentation yielded multiple zones within the stroke region that were characterized as low, pseudonormal, and high. The mean proportion of low:pseudonormal:high was 72%:20%:8%. CONCLUSIONS: Despite low average ADCW, computer-assisted segmentation of DW MRI detected heterogeneous zones within ischemic lesions corresponding to low, pseudonormal, and high ADCw not visible to the human eye. This supports acute elevation of ADCw in human ischemic stroke and, accordingly, different temporal rates of tissue evolution toward infarction.

Acute Disease↗

PubMed1987

The development of a pH-sensitive contrast agent for NMR 1H imaging.

Fe(III)meso-tetra(4-sulfonatophenyl)porphine (Fe-TPPS4) has been investigated as a potential pH-sensitive nuclear magnetic resonance (NMR) proton image contrast agent. Relaxation rates (1/T1 and 1/T2) of water protons were measured as a function of pH and concentration of Fe-TPPS4 in phosphate-buffered isotonic saline. Transverse relaxation rates (1/T2) did not change appreciably with pH above 6.0. Longitudinal relaxation rates (1/T1) increased significantly between pH 7.75 and 5.75. This effect was more pronounced with the increasing concentration of Fe-TPPS4 from 0.1 to 1.5 mM and is attributed to a pH-dependent equilibrium between the high-spin (S = 5/2) Fe-TPPS4 monomer at low pH and the antiferromagnetically coupled mu-oxodimer O-(FeTPPS4)2 at high pH. The efficacy of this pH-dependent contrast agent is demonstrated in vitro.

Contrast Media↗

PubMedDate not supplied

SAR reduced pulse sequences.

Three techniques were considered for reducing the RF (radiofrequency) power deposition in the body while maintaining scan time efficiency: reducing the RF peak amplitude while increasing the pulse width, substituting gradient echoes for spin echoes, and reducing the flip angle of the phase reversal pulse. The use of gradient echoes was found to be the most efficient means to reduce the power delivered to the patient and to obtain rapid data acquisition. The effect upon SAR (specific absorption rate) and SNR (signal-to-noise ratio) was demonstrated on a phantom when the phase reversal pulse was reduced from the standard 180 degrees to 90 degrees. Data in the body indicated a fairly constant SNR down to a refocusing flip angle between 110 degrees and 135 degrees. An initial clinical evaluation was performed at three institutions using the method of reducing the flip angle of the phase reversal pulse. The scan with theta = 120 degrees was rated by readers in a blinded study as having acceptable diagnostic image quality while the 135 degrees scan had comparable image quality to a conventional 90 degrees - 180 degrees pulse sequence. The use of reduced phase reversal pulses was seen as an efficient protocol to obtain T1-weighted images at rapid data rates while reducing the power delivered to the body by about 40%.

Humans↗