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Most current PET detector designs suffer from event mispositioning at high count rates, as scintillation light from nearby and nearly simultaneous gamma ray conversions becomes mixed. We have used the NEMA NU 2-2001 70 cm test phantom and a Na-22 point source to quantify this effect as a function of activity on two block-detector tomographs (the Siemens/CTI HR+ and the General Electric Discovery LS), and two Anger-type PET tomographs (the Siemens ECAM DUET and the Philips CPET+). After accounting for event losses due to dead time, we find that the number of counts on LORs passing through a cylinder of diameter and height equal to the point-source full width at tenth-maximum measured at low rate surrounding the point source decreases by between 9% (HR+) and 35% (CPET+) at the activity giving rise to peak noise equivalent count (NEC) rate. Mispositioned events act to reduce signal-to-noise ratio, both by reducing apparent activity at the originating location and by increasing the signal background. We have reformulated the conventional expression for NEC rate to account for this phenomenon. The new formulation of NEC, which we call NEC*, results in a lower peak value which in turn occurs at a lower activity concentration than for the conventional formulation. Index Terms--Count-rate, data quality, NEC, PET, pileup.

We have developed a three-dimensional (3-D) reconstruction procedure for positron emission tomography (PET) using stochastic sampling techniques--the SS3D algorithm. A forward- and back-projector pair has been developed that eliminates the need to explicitly calculate the system response matrix (SRM). This is advantageous as it eliminates the memory requirements for storing this matrix. As compared to on-the-fly methods, our method is more accurate in its assumptions and can readily incorporate various physical effects of attenuation, scatter, and detector characteristics. This method can be efficiently used with 'simultaneous' or 'row action' algorithms like image space reconstruction algorithm (ISRA), expectation maximization (EM), and ordered subsets expectation maximization (OSEM). We demonstrate the successful implementation of this technique with the maximum likelihood expectation maximization (ML-EM), maximum a posteriori expectation maximization (MAP-EM), and maximum a posteriori ordered subsets expectation maximization (MAP-OS-EM) algorithms by evaluating the images on the basis of uniformity of noise, contrast recovery, signal-to-noise ratio (SNR), point-spread function, structural accuracy, and computational time. Index Terms--Iterative reconstruction, Monte Carlo, stochastic techniques.

We have constructed and tested prototype PET detector modules incorporating wavelength-shifting fiber ribbons alternating with thin CsI(Na) scintillator plates in multilayer stacks. Modules with cross-sectional area of 11cm x 11cm and with 9mm of total crystal thickness have been tested. A reconstructed spatial resolution of 3 mm FWHM has been obtained for a line source, with an energy resolution of < 20% and a time resolution of 25ns FWHM. Energy measurements and coincidence timing are provided by 4 photomultipliers in an Anger array on one 11cm x 11cm module face. Multiplexed fiber readout has been implemented with multianode photomultipliers coupled to several fiber ribbons. The methods and resolution achieved are readily extended to larger systems in a straightforward and cost-effective manner. Results of tests with several phantoms are presented.

Presents a study that developed SS3D, a three-dimensional (3-D) image reconstruction procedure for positron emission tomography using stochastic sampling techniques. Framework of the SS3D method; Evaluation of the SS3D method; Optimization techniques for fully 3-D reconstruction; Results from the optimization techniques.

In the United States, legislative actions in over 28 states require radiologists to notify women who undergo breast screening mammography of their breast density. This has led to increased public interest in supplemental screening, but radiologists have not come to a consensus on a supplemental screening modality. In choosing between the most common options, whole-breast ultrasonography (US) and magnetic resonance (MR) imaging, one must weigh the benefits and drawbacks of each modality, as increased cancer detection may be accompanied by increased examination costs and biopsy rates. There has been recent interest in molecular breast imaging (MBI) for supplemental screening because of its high sensitivity, as well as its high specificity. This article describes how MBI fits into clinical practice alongside digital breast tomosynthesis (DBT), targeted US, and MR imaging. The authors describe their approach to breast cancer screening, which uses DBT as the primary imaging modality. DBT is complemented by automated density calculations and supplemented with functional imaging techniques, including MR imaging or MBI, for women with dense breasts. An algorithm based on the patient's breast cancer risk is used to determine if either MR imaging or MBI for supplemental screening is appropriate. MBI is also used as a problem-solving tool for the evaluation of clinical indications following complex mammography or US, or for unexplained physical findings. This article describes aspects related to implementing MBI in clinical practice, including the clinical workflow, patient management, radioactive tracer administration, and procedure reimbursement. © RSNA, 2017.

Objective: Molecular breast imaging was implemented in routine clinical practice at a large community-based breast imaging center. The aim of this study was to retrospectively assess the clinical performance of molecular breast imaging as a supplementary screening tool for women with dense breast tissue., Materials and Methods: Women with dense breasts and negative mammography results who subsequently underwent screening with 300 MBq (8 mCi) (99m)Tc-sestamibi molecular breast imaging were retrospectively analyzed. Outcome measures included cancer detection rate, recall rate, biopsy rate, and positive predictive values (PPVs)., Results: Molecular breast imaging screening of 1696 women in this study resulted in the detection of 13 mammographically occult malignancies, of which 11 were invasive, one was node positive, and one had unknown node positivity. The lesion size ranged from 0.6 to 2.4 cm, with a mean of 1.1 cm. The incremental cancer detection rate was 7.7‰ (95% CI, 4.5-13.1‰), the recall rate was 8.4% (95% CI, 7.2-9.8%), and the biopsy rate was 3.7% (95% CI, 2.9%-4.7%). The PPV for recall (PPV 1) was 9.1% (95% CI, 5.4-15.0%), and the PPV for biopsy (PPV 3) was 19.4% (95% CI, 11.4-30.9%)., Conclusion: When incorporated into a community-based clinical practice environment, molecular breast imaging yielded a high incremental cancer detection rate of 7.7‰ at an acceptable radiation dose. These results show the utility of molecular breast imaging as a supplementary screening tool to mammography for women with dense breasts.

We develop and implement a compressive reconstruction method for tomographic recovery of refractive index distribution for weakly attenuating objects in a microfocus x-ray system. This is achieved through the development of a discretized operator modeling both the transport of intensity equation and the x-ray transform that is suitable for iterative reconstruction techniques.

Preclinical SPECT offers a powerful means to understand the molecular pathways of drug interactions in animal models by discovering and testing new pharmaceuticals and therapies for potential clinical applications. A combination of high spatial resolution and sensitivity are required in order to map radiotracer uptake within small animals. Pinhole collimators have been investigated, as they offer high resolution by means of image magnification. One of the limitations of pinhole geometries is that increased magnification causes some rays to travel through the detection scintillator at steep angles, introducing parallax errors due to variable depth-of-interaction in scintillator material, especially towards the edges of the detector field of view. These parallax errors ultimately limit the resolution of pinhole preclinical SPECT systems, especially for higher energy isotopes that can easily penetrate through millimeters of scintillator material. A pixellated, focused-cut (FC) scintillator, with its pixels laser-cut so that they are collinear with incoming rays, can potentially compensate for these parallax errors and thus improve the system resolution. We performed the first experimental evaluation of a newly developed focused-cut scintillator. We scanned a Tc-99m source across the field of view of pinhole gamma camera with a continuous scintillator, a conventional "straight-cut" (SC) pixellated scintillator, and a focused-cut scintillator, each coupled to an electron-multiplying charge coupled device (EMCCD) detector by a fiber-optic taper, and compared the measured full-width half-maximum (FWHM) values. We show that the FWHMs of the focused-cut scintillator projections are comparable to the FWHMs of the thinner SC scintillator, indicating the effectiveness of the focused-cut scintillator in compensating parallax errors.