Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

We review positron-emission tomography (PET), which has inherent advantages that avoid the shortcomings of other nuclear medicine imaging methods. PET image reconstruction methods with origins in signal and image processing are discussed, including the potential problems of these methods. A summary of statistical image reconstruction methods, which can yield improved image quality, is also presented.

/pdf/positron-emission-tomography-3ouih7jh8d.pdf

Positron-emission tomography

The expectation-maximization (EM) method can facilitate maximizing likelihood functions that arise in statistical estimation problems. In the classical EM paradigm, one iteratively maximizes the conditional log-likelihood of a single unobservable complete data space, rather than maximizing the intractable likelihood function for the measured or incomplete data. EM algorithms update all parameters simultaneously, which has two drawbacks: 1) slow convergence, and 2) difficult maximization steps due to coupling when smoothness penalties are used. The paper describes the space-alternating generalized EM (SAGE) method, which updates the parameters sequentially by alternating between several small hidden-data spaces defined by the algorithm designer. The authors prove that the sequence of estimates monotonically increases the penalized-likelihood objective, derive asymptotic convergence rates, and provide sufficient conditions for monotone convergence in norm. Two signal processing applications illustrate the method: estimation of superimposed signals in Gaussian noise, and image reconstruction from Poisson measurements. In both applications, the SAGE algorithms easily accommodate smoothness penalties and converge faster than the EM algorithms. >

https://web.eecs.umich.edu/~fessler/papers/files/jour/94/web/fessler-94-sag.pdf

Space-alternating generalized expectation-maximization algorithm

Molecular imaging is revolutionizing the way we study the inner workings of the human body, diagnose diseases, approach drug design, and assess therapies. The field as a whole is making possible the visualization of complex biochemical processes involved in normal physiology and disease states, in real time, in living cells, tissues, and intact subjects. In this review, we focus specifically on molecular imaging of intact living subjects. We provide a basic primer for those who are new to molecular imaging, and a resource for those involved in the field. We begin by describing classical molecular imaging techniques together with their key strengths and limitations, after which we introduce some of the latest emerging imaging modalities. We provide an overview of the main classes of molecular imaging agents (i.e., small molecules, peptides, aptamers, engineered proteins, and nanoparticles) and cite examples of how molecular imaging is being applied in oncology, neuroscience, cardiology, gene therapy, cell tracking, and theranostics (therapy combined with diagnostics). A step-by-step guide to answering biological and/or clinical questions using the tools of molecular imaging is also provided. We conclude by discussing the grand challenges of the field, its future directions, and enormous potential for further impacting how we approach research and medicine.

A Molecular Imaging Primer: Modalities, Imaging Agents, and Applications

The sympathetic nervous system in heart failure physiology, pathophysiology, and clinical implications.

Meta-iodobenzylguanidine (M-IBG), an iodinated aromatic analog of the hypotensive drug guanethidine, 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 norepinephrine 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.

https://jnm.snmjournals.org/content/jnumed/22/1/22.full.pdf

Myocardial Imaging with a Radioiodinated Norepinephrine Storage Analog

An evaluation of radioiodinated meta-iodobenzylguanidine (m-IBG) as an adrenomedullary imaging agent is reported in 15 rhesus monkeys. Scintiscans of the monkey adrenal medulla have been obtained with (/sup 123/I)- and (m-/sup 131/)IBG at 2 to 6 days after injection. The imaging superiority of m-IBG over its positional isomer, para-iodobenzylguanidine (p-IBG), is documented in both dogs and monkeys. Administration of reserpine, a depletor of catecholamine stores, markedly lowers the (m-/sup 131/I)-IBG content of the dog adrenal medulla, but the adrenergic blocking agents phenoxybenzamine and propanolol have no effect. Subcellular fractionation of the dog's adrenal medullae reveals that m-IBG is sequestered mainly in the chromaffin storage granules. The results of this study suggest that radioiodinated m-IBG, previously reported to image the primate myocardium, also merits evaluation as a clinical radiopharmaceutical for the adrenal medulla.

https://jnm.snmjournals.org/content/jnumed/22/4/358.full.pdf

Imaging the primate adrenal medulla with [123I] and [131I] meta-iodobenzylguanidine: concise communication.

A Maximum Likelihood (ML) image reconstruction technique using list-mode data has been applied to Compton scattering camera imaging. List-mode methods are appealing in Compton camera image reconstruction because the total number of data elements in the list (the number of detected photons) is significantly smaller than the number of possible combinations of position and energy measurements, leading to a much smaller problem than that faced by traditional iterative reconstruction techniques. For a realistic size device, the number of possible detector bins can be as large as 10 billion per pixel of the image space, while the number of counted photons would typically be a very small fraction of that. The primary difficulty in applying the list-mode technique is in determining the parameters which describe the response of the imaging system. In this work, a simple method for determining the required system matrix coefficients is employed, in which a back-projection is performed in list-mode, and response coefficients determined for only tallied pixels. Projection data has been generated for a representative Compton camera system by Monte Carlo simulation for disk sources with hot and cold spots and energies of 141, 364, and 511 keV, and reconstructions performed.

/pdf/list-mode-maximum-likelihood-reconstruction-of-compton-1g2ry39fh7.pdf

List-mode maximum likelihood reconstruction of Compton scatter camera images in nuclear medicine

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.

https://jnm.snmjournals.org/content/jnumed/31/1/90.full.pdf

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

An emission transaxial tomographic system using a scintillation camera as the detector is described. The unit allows accurate positioning of a scintillation camera's detector at any angle around a patient in order to obtain the multiple projection images needed for transaxial tomography, and it is capable of imaging any area of the body. The camera can also be used for all types of conventional imaging procedures. Image processing is performed by a small on-line computer. A convolution algorithm and a mathematical technique for approximate absorption correction are used to obtain high-resolution and high-contrast images with good quantitative accuracy. The operation of the system is described and representative phantom and patient studies are presented to illustrate the capabilities of the system.

https://jnm.snmjournals.org/content/jnumed/18/4/381.full.pdf

W.L. Rogers

Papers

Myocardial Imaging with a Radioiodinated Norepinephrine Storage Analog

Imaging the primate adrenal medulla with [123I] and [131I] meta-iodobenzylguanidine: concise communication.

List-mode maximum likelihood reconstruction of Compton scatter camera images in nuclear medicine

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

The Humongotron--a scintillation-camera transaxial tomograph