Biomedical subjects

J P Leal

Publications and source records attributed to J P Leal.

4 recordsLinked to original sources

PubMed1992

Improved positron emission tomography quantification by Fourier-based restoration filtering.

Positron emission tomography (PET) images are characterized by both poor spatial resolution and high statistical noise. Conventional methods to reduce noise, such as local weighted averaging, produce further deteriorations in spatial resolution, while the use of deconvolution to recover resolution typically amplifies noise to unacceptable levels. We studied the use of two-dimensional Fourier filtering to simultaneously increase quantitative recovery and reduce noise. The filter was based on inversion of the scanner's measured transfer function, coupled with high frequency roll-off. In phantom studies, we found improvements in both "hot" and "cold" sphere quantification. Compared with ramp-only filtering, improvements in hot spot recovery for the highest accuracy filter averaged 13.6% +/- 6.6% for spheres larger than 15 mm; improvements in cold spot recovery averaged 30.7% +/- 4.7%. At the same time, the noise was reduced by a factor of 3 compared with randomly filtering. Fourier-based image restoration filtering is thus capable of improving both accuracy and precision in PET.

Brain↗

PubMed1992

Measurement of radiotracer concentration in brain gray matter using positron emission tomography: MRI-based correction for partial volume effects.

Accuracy in in vivo quantitation of brain function with positron emission tomography (PET) has often been limited by partial volume effects. This limitation becomes prominent in studies of aging and degenerative brain diseases where partial volume effects vary with different degrees of atrophy. The present study describes how the actual gray matter (GM) tracer concentration can be estimated using an algorithm that relates the regional fraction of GM to partial volume effects. The regional fraction of GM was determined by magnetic resonance imaging (MRI). The procedure is designated as GM PET. In computer simulations and phantom studies, the GM PET algorithm permitted a 100% recovery of the actual tracer concentration in neocortical GM and hippocampus, irrespective of the GM volume. GM PET was applied in a test case of temporal lobe epilepsy revealing an increase in radiotracer activity in GM that was undetected in the PET image before correction for partial volume effects. In computer simulations, errors in the segmentation of GM and errors in registration of PET and MRI images resulted in less than 15% inaccuracy in the GM PET image. In conclusion, GM PET permits accurate determination of the actual radiotracer concentration in human brain GM in vivo. The method differentiates whether a change in the apparent radiotracer concentration reflects solely an alteration in GM volume or rather a change in radiotracer concentration per unit volume of GM.

Algorithms↗

PubMedDate not supplied

Anatomical localization for PET using MR imaging.

Accurate localization of an imaging plane of interest is often needed prior to a positron emission tomographic (PET) study. We have developed a simple method for accurate and reproducible selection of an imaging plane for PET using magnetic resonance (MR) imaging. This method is useful when optimal sampling of specific brain structures, such as small subcortical nuclei, or when a specific imaging angle is required for the PET study. An external localizing device, consisting of a series of tubes visible on MR, is affixed to an individually fitted thermoplastic mask. This mask system is worn by the patient during both the MR and PET studies. A plane of interest is planned from the sagittal MR image and defined by its relation to the localizing device and to the MR scanner's "landmark" or reference position. This plane is transferred to the mask by means of a calibrated alignment laser. The coplanar acquisition of MR and PET images allows individualized analysis of brain structure-function relationships. Phantom studies demonstrated the accuracy and reproducibility of imaging plane selection by this method to be within 1 mm and 1 degree. Application of the localization protocol in a human subject is also presented.

Adult↗

PubMedDate not supplied

Correction of PET data for partial volume effects in human cerebral cortex by MR imaging.

Due to the limited spatial resolution of positron emission tomography (PET), the accuracy of quantitative measurements of regional metabolism or neuroreceptor concentration is influenced by partial volume averaging of brain with CSF, bone, and scalp. This effect is increased in the presence of cortical atrophy, as in patients with Alzheimer disease (AD). Correction for this underestimation in PET measurements is necessary for the comparison of AD patients and normal controls. We have developed a method for three-dimensional correction of human PET data using magnetic resonance (MR) imaging. A composite brain tissue image is created by summing the binary representation of nine MR images, weighted to the PET z-axis line-spread function. This composite tissue image is convolved to the resolution of the PET image. The original PET image is divided by the convolved tissue image on a pixel-by-pixel basis, resulting in an atrophy-corrected PET image in which count density represents activity per volume of brain tissue rather than spatial volume. This has been performed in [11C]carfentanil mu-opiate receptor PET studies of the temporal cortex in two AD patients and one normal volunteer. After correction, average regional increases in count density were 11% (range = 4-21%) in the normal and 46% (range = 28-99%) and 48% (range = 14-109%) in the patient studies. The accuracy of this method of partial volume correction was estimated using a spherical phantom.

Aged↗