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N H Clinthorne

Publications and source records attributed to N H Clinthorne.

13 recordsLinked to original sources
PubMed2004

A modified uniform Cramer-Rao bound for multiple pinhole aperture design.

This paper presents a modified Uniform Cramer-Rao bound (UCRB) for studying estimator spatial resolution and variance tradeoffs. We proposed to use a resolution constraint that is imposed on mean gradient vectors of achieved estimators and derived the minimum achievable variance for any estimator satisfies this resolution constraint. This approach partially overcomes the limitations of the former UCRB approach based on a bias-gradient norm constraint. We applied this method in a feasibility study of using multiple pinhole apertures for small animal SPECT imaging applications. The SPECT system studied was based on an existing gamma camera. The achievable spatial resolution and variance tradeoffs for systems with different design parameters, such as number of pinholes and pinhole size, were studied.

Animals↗
PubMed2000

Penalized weighted least-squares image reconstruction for dual energy X-ray transmission tomography.

We present a dual-energy (DE) transmission computed tomography (CT) reconstruction method. It is statistically motivated and features nonnegativity constraints in the density domain. A penalized weighted least squares (PWLS) objective function has been chosen to handle the non-Poisson noise added by amorphous silicon (aSi:H) detectors. A Gauss-Seidel algorithm has been used to minimize the objective function. The behavior of the method in terms of bias/standard deviation tradeoff has been compared to that of a DE method that is based on filtered back projection (FBP). The advantages of the DE PWLS method are largest for high noise and/or low flux cases. Qualitative results suggest this as well. Also, the reconstructed images of an object with opaque regions are presented. Possible applications of the method are: attenuation correction for positron emission tomography (PET) images, various quantitative computed tomography (QCT) methods such as bone mineral densitometry (BMD), and the removal of metal streak artifacts.

Algorithms↗
PubMed1997

Grouped-coordinate ascent algorithms for penalized-likelihood transmission image reconstruction.

This paper presents a new class of algorithms for penalized-likelihood reconstruction of attenuation maps from low-count transmission scans. We derive the algorithms by applying to the transmission log-likelihood a version of the convexity technique developed by De Pierro for emission tomography. The new class includes the single-coordinate ascent (SCA) algorithm and Lange's convex algorithm for transmission tomography as special cases. The new grouped-coordinate ascent (GCA) algorithms in the class overcome several limitations associated with previous algorithms. 1) Fewer exponentiations are required than in the transmission maximum likelihood-expectation maximization (ML-EM) algorithm or in the SCA algorithm. 2) The algorithms intrinsically accommodate nonnegativity constraints, unlike many gradient-based methods. 3) The algorithms are easily parallelizable, unlike the SCA algorithm and perhaps line-search algorithms. We show that the GCA algorithms converge faster than the SCA algorithm, even on conventional workstations. An example from a low-count positron emission tomography (PET) transmission scan illustrates the method.

Algorithms↗
PubMed1991

Testing of local gamma-ray scatter fractions determined by spectral fitting.

The spectral-fitting method of correction for gamma-ray Compton scattering within objects separates the unscattered and scattered components of locally measured energy spectra. Here, we employ a third-order polynomial for the scattering and an approximately constant fitting window. A scatter fraction, defined as total scattered over total unscattered counts within a 20% window, is calculated for each point in our Anger camera images. These scatter fractions are tested against those from Monte-Carlo simulation for 99mTc and against results from semiconductor detector measurements for 131I. A radioactive sphere at several locations within a non-radioactive cylinder and the inverse are imaged for the testing. For one case, reproducibility of the spectral-fitting scatter fraction as a function of the number of unscattered counts within the 20% acceptance window was also determined. With 99mTc, for all cases, the agreement between spectral fitting and the standard estimation method is within 16%. With 131I, for the 'hot' sphere at two locations, the agreement is within 21%. For the 'hot' sphere at the third location (off the cylinder axis towards the camera), the dependence of scatter fraction on transverse distance is good although the absolute values are too large. Scatter fraction reproducibility is within 10% for 1000 or more counts. Therefore, further testing of spectral fitting and initial application to realistic clinical images seem to be in order.

Gamma Cameras↗
PubMed1991

Clinical SPRINT imaging. Preliminary results compared to conventional SPECT brain scanning using Tc-99m HMPAO.

We have performed initial clinical studies using the high resolution single photon ring tomograph (SPRINT) and Tc-99m HMPAO. To determine what additional anatomic detail can be depicted using this high resolution, dedicated head, multidetector SPECT device compared to conventional SPECT, six patients with stroke and one normal volunteer were imaged after the injection of 20 mCi Tc-99m HMPAO on a conventional rotating Anger gamma camera (GE-400AC), followed immediately by imaging on SPRINT. Imaging acquisition on the GE-400AC gamma camera was performed using 360 degrees rotation, 64 stops, at 30 sec/stop, yielding an average of 985,714 counts for a 10.0 mm thick slice. GE-400AC images were of good quality, having in-plane full width half maximum (FWHM) resolution of approximately 15 mm. SPRINT acquisition of image data was performed using both the high resolution and high sensitivity apertures, with data collection over 15 or 20 minutes of imaging time accumulating approximately 500,000 counts and 1,000,000 counts, respectively, from patients in a 10.0 mm thick slice, achieving an in-plane FWHM resolution of approximately 8 mm and 10 mm for the two apertures, respectively. Both image resolution and contrast for visualization of gray, white, and cerebral spinal fluid filled brain structures were improved using SPRINT compared with the GE-400AC. We conclude that SPRINT is well suited for brain imaging with Tc-99m HMPAO and is of particular value for applications demanding high resolution.

Adult↗
PubMed1990

SPECT dual-energy-window Compton correction: scatter multiplier required for quantification.

The dual-energy window Compton-scattering correction technique is defined here especially for accurate quantification of focal regions having higher than average uptake. The quantification is relative to a known-activity reference source. The scatter multiplier ("k" value) is determined for a radioactive 99mTc sphere on or off the axis of a cylinder containing water with or without background. Both maximum likelihood and filtered-backprojection reconstruction are employed. Either projections or tomograms are corrected. With tight regions of interest, there is a tendency for the requisite "k" value to be slightly lower as the diameter of the cylinder is increased. Neither sphere location nor background perturbs "k", however, so a constant value is a good, first approximation. Then a two-sphere validation test yields an accuracy of 8% with subtracted-tomograms ("k" = 1.30) and 2% with subtracted-projections ("k" = 1.20). With a reference-source region of interest which is four times larger, "k" is reduced and also now depends on background. Although equivalent quantitatively, maximum likelihood is preferable to filtered backprojection with Chang attenuation correction since it produces a less-noisy image.

Algorithms↗
PubMed1988

SPECT Compton-scattering correction by analysis of energy spectra.

The hypothesis that energy spectra at individual spatial locations in single photon emission computed tomographic projection images can be analyzed to separate the Compton-scattered component from the unscattered component is tested indirectly. An axially symmetric phantom consisting of a cylinder with a sphere is imaged with either the cylinder or the sphere containing 99mTc. An iterative peak-erosion algorithm and a fitting algorithm are given and employed to analyze the acquired spectra. Adequate separation into an unscattered component and a Compton-scattered component is judged on the basis of filtered-backprojection reconstruction of corrected projections. In the reconstructions, attenuation correction is based on the known geometry and the total attenuation cross section for water. An independent test of the accuracy of separation is not made. For both algorithms, reconstructed slices for the cold-sphere, hot-surround phantom have the correct shape as confirmed by simulation results that take into account the measured dependence of system resolution on depth. For the inverse phantom, a hot sphere in a cold surround, quantitative results with the fitting algorithm are accurate but with a particular number of iterations of the erosion algorithm are less good. (A greater number of iterations would improve the 26% error with the algorithm, however.) These preliminary results encourage us to believe that a method for correcting for Compton-scattering in a wide variety of objects can be found, thus helping to achieve quantitative SPECT.

Algorithms↗
PubMed1986

Development of a kit-form analog of metaiodobenzylguanidine.

The synthesis and evaluation of two radiopharmaceutical analogs of metaiodobenzylguanidine (MIBG) are described. Unlike MIBG, these analogs are rapidly and conveniently radioiodinated at room temperature in clinically applicable kit form. Radioiodinated 4-amino-3-iodobenzylguanidine (AIBG) for injection is synthesized in 20 min using IODO-GEN as the radioiodide oxidant and an anion exchange filter for purification. AIBG shows an affinity for the heart and adrenal medullae of dog and monkey similar to that of MIBG. In addition, AIBG shows improved selectivity for the adrenergic nerves of the heart as demonstrated by chemical sympathectomy studies. Tomographic images of the dog heart and planar images of the dog adrenal medullae were obtained using [123I]AIBG and [131I]AIBG, respectively. Planar images of the monkey heart using [131I]AIBG were similar in quality to those reported previously with [131I]MIBG. In view of the facile radiosynthesis of AIBG, a clinical evaluation of this new agent is warranted.

3-Iodobenzylguanidine↗
PubMed1984

Performance evaluation of SPRINT, a single photon ring tomography for brain imaging.

SPRINT, a prototype single photon tomograph, has been designed primarily for high-resolution brain imaging in humans with I-123-labeled compounds such as iodoamphetamine, hydroxyiodopropyldiamine (HIPDM), and iodobenzene (IBZ). SPRINT uses a ring of stationary, discrete Nal detectors, and fan-beam sampling is accomplished with a rotating eight-slit aperture ring that acquires a complete projection set in 1/8 revolution. In-plane and cross-plane resolutions are 8mm and 10mm FWHM, respectively, measured on axis. Sensitivity with an 18% energy window is 1000 cprs per microCi/cc for Tc-99m in a 20 cm diameter phantom. A detailed evaluation of system performance has been completed, and preliminary human brain blood flow images have been obtained using HIPDM.

Brain↗
PubMed1982

Field-flood requirements for emission computed tomography with an Anger camera.

Emission computed tomography with a rotating camera places stringent requirements on camera uniformity and the stability of camera response. In terms of clinical tomographic imaging, we have studied the statistical accuracy required for camera flood correction, the requirements for flood accuracy, the utility and validity of flood and data image smoothing to reduce random noise effects, and the magnitude and effect of camera variations as a function of angular position, energy window, and tuning. Uniformity of the corrected flood response must be held to better than 1% to eliminate image artifacts that are apparent in a million-count image of a liver slice. This requires calibration with an accurate, well-mixed flood source. Both random fluctuations and variations in camera response with rotation must be kept below 1%. To meet the statistical limit, one requires at least 30 million counts for the flood-correction image. Smoothing the flood image alone introduces unacceptable image artifacts. Smoothing both the flood image and data, however, appears to be a good approach toward reducing noise effects. Careful camera tuning and magnetic shield design provide camera stability suitable for present clinical applications.

Evaluation Studies as Topic↗
PubMed1981

Oblique-angle tomography: a restructuring algorithm for transaxial tomographic data.

A set of contiguous transaxial tomographic sections obtained with a rotating-camera tomograph represents the full three-dimensional distribution of activity within a volume of the body. Tomographic sections in planes other than the origianl transverse plane can be produced from these data merely by resorting the data appropriately. The paper presents a simple and efficient algorithm for producing tomograms of the heart oriented either at right angles to the long axis of the left ventricle, or parallel to it. Tomograms in these orientations have specific advantages for imaging the heart and avoid some of the limitations seen in comparable tomograms obtained by the seven-pinhole technique.

Heart↗
PubMed1981

Myocardial imaging with a radioiodinated norepinephrine storage analog.

Meta-iodobenzylguanidine (M-IBG), an iodinated aromatic analog of the hypotensive drug quanethidine, localizes in the heart of the rat, dog, and rhesus monkey. A comparative study of tissue distribution in the dog has been performed with five myocardiophilic agents: thallium-201, I-125 16-iodohexadecanoic acid, H-3 norepinephrine, C-14 guanethidine and I-125 M-IBG. The last two compounds give heart concentrations and heart-to-blood concentration ratios similar to those of thallium-201. Planar and tomographic images of the hearts of the dog and rhesus monkey were obtained using I-131 or I-123 labeled M-IBG. Blocking studies with reserpine suggest that a major component of myocardial retention of M-IBG is sequestration within the norephinephrine storage vesicles of the adrenergic nerves. The localization of M-IBG in other organs with rich sympathetic innervation and the relative insensitivity of myocardial uptake to a wide range of loading doses lend additional support for a neuronal mode of retention.

3-Iodobenzylguanidine↗