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The discovery of the first two interstellar objects implies that, on average, every star contributes a substantial amount of material to the galactic population by ejecting such bodies from the host system. Since scattering is a chaotic process, a comparable amount of material should be injected into the inner regions of each system that ejects comets. For comets that are transported inwards and interact with planets, this Letter estimates the fraction of material that is accreted or outward-scattered as a function of planetary masses and orbital parameters. These calculations indicate that planets with escape velocities smaller than their current day orbital velocities will efficiently accrete comets. We estimate the accretion efficiency for members of the current census of extrasolar planets, and find that planetary populations including but not limited to hot and warm Jupiters, sub-Neptunes and super-Earths can efficiently capture incoming comets. This cometary enrichment may have important ramifications for post-formation atmospheric composition and chemistry. As a result, future detections and compositional measurements of interstellar comets will provide direct measurements of material that potentially enriched a sub-population of the extrasolar planets. Finally, we estimate the efficiency of this enrichment mechanism for extrasolar planets that will be observed with the $\textit{James Webb Space Telescope}$ (JWST). With JWST currently operational and these observations imminently forthcoming, it is of critical importance to investigate how enrichment from interstellar comet analogues may affect the interpretations of exoplanet atmospheric compositions., Accepted for publication at ApJL, 9 pages, 3 figures, preprint for reference at Exoplanets IV Program Number 405.03

Inpatients with cancer are at the greatest risk for falling. Although studies have identified the characteristics of patients with cancer who fall, few studies have focused on the characteristics of patients with blood cancers who fall.The objectives of this study are to identify characteristics of inpatients with blood cancers who fall and implement fall-mitigation efforts through an enhanced assessment of chemotherapy-induced peripheral neuropathy.Descriptive design and retrospective review of 51 patient falls were used to identify characteristics of inpatients with cancer who fell.The majority of patients who fell were male (n = 33), and most falls occurred during the day shift (n = 24). Few patients were listed on the Morse Fall Risk Scale for mental status and forgetting limitations (n = 7), and most were not identified as a high fall risk (n = 30). The majority of falls were associated with toileting needs (n = 32). Patients spent a mean of 12.73 days in the hospital before falling. Thirty-two patients received chemotherapy prior to their fall, 25 of whom received neurotoxic chemotherapy.

Water worlds have been hypothesized as an alternative to photo-evaporation in order to explain the gap in the radius distribution of Kepler exoplanets. We explore water worlds within the framework of a joint mass-radius-period distribution of planets fit to a sample of transiting Kepler exoplanets, a subset of which have radial velocity mass measurements. We employ hierarchical Bayesian modeling to create a range of ten mixture models that include multiple compositional subpopulations of exoplanets. We model these subpopulations - including planets with gaseous envelopes, evaporated rocky cores, evaporated icy cores, intrinsically rocky planets, and intrinsically icy planets - in different combinations in order to assess which combinations are most favored by the data. Using cross-validation, we evaluate the support for models that include planets with icy compositions compared to the support for models that do not, finding broad support for both. We find significant population-level degeneracies between subpopulations of water worlds and planets with primordial envelopes. Among models that include one or more icy-core subpopulations, we find a wide range for the fraction of planets with icy compositions, with a rough upper limit of 50%. Improved datasets or alternative modeling approaches may better be able to distinguish between these subpopulations of planets., Comment: 31 pages, 10 figures, accepted for publication in ApJ

This report summarizes and highlights the fifth International RASopathies Symposium: When Development and Cancer Intersect, held in Orlando, Florida in July 2017. The RASopathies comprise a recognizable pattern of malformation syndromes that are caused by germ line mutations in genes that encode components of the RAS/mitogen-activated protein kinase (MAPK) pathway. Because of their common underlying pathogenetic etiology, there is significant overlap in their phenotypic features, which includes craniofacial dysmorphology, cardiac, cutaneous, musculoskeletal, gastrointestinal and ocular abnormalities, neurological and neurocognitive issues, and a predisposition to cancer. The RAS pathway is a well-known oncogenic pathway that is commonly found to be activated in somatic malignancies. As in somatic cancers, the RASopathies can be caused by various pathogenetic mechanisms that ultimately impact or alter the normal function and regulation of the MAPK pathway. As such, the RASopathies represent an excellent model of study to explore the intersection of the effects of dysregulation and its consequence in both development and oncogenesis.

The Kepler, K2 and TESS transit surveys are revolutionizing our understanding of planets orbiting close to their host stars and our understanding of exoplanet systems in general, but there remains a gap in our understanding of wide-orbit planets. This gap in our understanding must be filled if we are to understand planet formation and how it affects exoplanet habitability. We summarize current and planned exoplanet detection programs using a variety of methods: microlensing (including WFIRST), radial velocities, Gaia astrometry, and direct imaging. Finally, we discuss the prospects for joint analyses using results from multiple methods and obstacles that could hinder such analyses. We endorse the findings and recommendations published in the 2018 National Academy report on Exoplanet Science Strategy. This white paper extends and complements the material presented therein., Astro2020 Science White paper

The Habitable-Exoplanet Observatory (HabEx) is a candidate flagship mission being studied by NASA and the astrophysics community in preparation of the 2020 Decadal Survey. The first HabEx mission concept that has been studied is a large (~4m) diffraction-limited optical space telescope, providing unprecedented resolution and contrast in the optical, with extensions into the near ulttraviolet and near infrared domains. We report here on our team’s efforts in defining a scientifically compelling HabEx mission that is technologically executable, affordable within NASA’s expected budgetary envelope, and timely for the next decade. We also briefly discuss our plans to explore less ambitious, descoped missions relative to the primary mission architecture discussed here.

In radionuclide treatment, tumor cells are primarily destroyed by charged particles emitted by the compound while associated higher energy photons are used to image the tumor in order to determine radiation dose and monitor shrinkage. However, the higher energy photons are difficult to image with conventional collimated Anger cameras, since a tradeoff exists between resolution and sensitivity, and the collimator septal penetration and scattering is increased due to the high energy photons. This research compares imaging performance of the conventional Anger camera to a Compton imaging system that can have improved spatial resolution and sensitivity for high energy photons because this tradeoff is decoupled, and the effect of Doppler broadening at higher gamma energies is decreased. System performance is analyzed by the modified uniform Cramer-Rao bound (M-UCRB) algorithms based on the developed system modeling. The bound shows that the effect of Doppler broadening is the limiting factor for Compton camera performance for imaging 364.4 keV photons emitted from 131I. According to the bound, the Compton camera outperforms the collimated system for an equal number of detected events when the desired spatial resolution for a 26 cm diameter uniform disk object is better than 12 mm FWHM. For a 3D cylindrical phantom, the lower bound on variance for the collimated camera is greater than for the Compton imaginer over the resolution range from 0.5 to 2 cm FWHM. Furthermore, the detection sensitivity of the proposed Compton imaging system is about 15-20 times higher than that of the collimated Anger camera.

A very high resolution positron emission tomography (PET) scanner for small animal imaging based on the idea of inserting a ring of high-granularity solid-state detectors into a conventional PET scanner is under investigation. A particularly interesting configuration of this concept, which takes the form of a degenerate Compton camera, is shown capable of providing sub-millimeter resolution with good sensitivity. We present a Compton PET system and estimate its performance using a proof-of-concept prototype. A prototype single-slice imaging instrument was constructed with two silicon detectors 1 mm thick, each having 512 1.4 mm x 1.4 mm pads arranged in a 32 x 16 array. The silicon detectors were located edgewise on opposite sides and flanked by two non-position sensitive BGO detectors. The scanner performance was measured for its sensitivity, energy, timing, spatial resolution and resolution uniformity. Using the experimental scanner, energy resolution for the silicon detectors is 1%. However, system energy resolution is dominated by the 23% FWHM BGO resolution. Timing resolution for silicon is 82.1 ns FWHM due to time-walk in trigger devices. Using the scattered photons, time resolution between the BGO detectors is 19.4 ns FWHM. Image resolution of 980 microm FWHM at the center of the field-of-view (FOV) is obtained from a 1D profile of a 0.254 mm diameter (18)F line source image reconstructed using the conventional 2D filtered back-projection (FBP). The 0.4 mm gap between two line sources is resolved in the image reconstructed with both FBP and the maximum likelihood expectation maximization (ML-EM) algorithm. The experimental instrument demonstrates sub-millimeter resolution. A prototype having sensitivity high enough for initial small animal images can be used for in vivo studies of small animal models of metabolism, molecular mechanism and the development of new radiotracers.

A sensitive screening approach for lung cancer could markedly reduce the high mortality rate for this disease. Previous studies have shown that methylation of gene promoters is present in exfoliated cells within sputum prior to lung cancer diagnosis. The purpose of the current study is to conduct a nested case-control study of incident lung cancer cases from an extremely high-risk cohort for evaluating promoter methylation of 14 genes in sputum. Controls (n = 92) were cohort members matched to cases (n = 98) by gender, age, and month of enrollment. The comparison of proximal sputum collected within 18 months to >18 months prior to diagnosis showed that the prevalence for methylation of gene promoters increased as the time to lung cancer diagnosis decreased. Six of 14 genes were associated with a >50% increased lung cancer risk. The concomitant methylation of three or more of these six genes was associated with a 6.5-fold increased risk and a sensitivity and specificity of 64%. This is the first study to prospectively examine a large panel of genes for their ability to predict lung cancer and shows the promise of gene promoter hypermethylation in sputum as a molecular marker for identifying people at high risk for cancer incidence. (Cancer Res 2006; 66(6): 3338-44)

In this paper, we present a novel approach to scintimammography that is based on the Compton camera principle. We analyse the performance of our scheme using Monte Carlo simulations. In particular, we evaluate the detection efficiency, spatial resolution and lesion visibility of the system at several gamma photon energies. The simulation results show that the proposed technique achieves an absolute detection efficiency of 0.03 and a full width at half maximum resolution of 3.8 mm at 141 keV photon energy for point sources 2.5 cm deep in a 5 cm thick breast phantom using 5 mm thick silicon detectors. Furthermore, our approach shows good performance in lesion detection, especially at high gamma photon energies, where mechanically collimated systems perform poorly due to severe septal penetration. With total collected counts of 1.35 million, equivalent to a 30 s acquisition time for an activity concentration level of 3.7 kBq ml(-1) (100 nCi cm(-3)) in normal breast tissue, and a tumour-to-background ratio of 8:1, our system can clearly reveal an 8 mm diameter tumour that is located 2.5 cm deep in a 500 ml breast phantom. We also present a simulation-based quantitative performance comparison between the proposed scintimammographic system and the compact collimated scintimammographic system in the task of lesion detection under a clinical imaging situation using a non-prewhitening matched filter observer model. Our comparison demonstrates that for the same imaging time, the two systems have a comparable performance in detecting an 8 mm tumour at 141 keV, with the proposed system performing marginally better. However, the proposed scintimammographic system clearly outperforms the compact collimated counterpart in the detection of a 5 mm tumour. We also investigate the contribution of scatter and direct radiation from adjacent organs. We find that the background contribution of liver to the right breast is 30% at 141 keV, which can be reduced to 4.8% with shielding.

The Cramer–Rao lower bound on estimator variance is used as a tool for assessing radiation detector requirements for nuclear medicine imaging. The classical bound for unbiased estimators is reviewed and its relationship to the well-known propagation-of-error formula is demonstrated. The uniform Cramer–Rao bound is described for situations where unbiased estimation is impractical such as in tomographic imaging. The bounds are used to evaluate the necessary detector requirements for a CsI(Tl)/Si photodiode scintillation camera, and to compare the performance of a Compton-scatter camera to that of a parallel-hole collimator/Anger camera system.

NASA's Kepler Mission has revealed two transiting planets orbiting Kepler-68. Follow-up Doppler measurements have established the mass of the innermost planet and revealed a third jovian-mass planet orbiting beyond the two transiting planets. Kepler-68b, in a 5.4 day orbit has mass 8.3 +/- 2.3 Earth, radius 2.31 +/- 0.07 Earth radii, and a density of 3.32 +/- 0.92 (cgs), giving Kepler-68b a density intermediate between that of the ice giants and Earth. Kepler-68c is Earth-sized with a radius of 0.953 Earth and transits on a 9.6 day orbit; validation of Kepler-68c posed unique challenges. Kepler-68d has an orbital period of 580 +/- 15 days and minimum mass of Msin(i) = 0.947 Jupiter. Power spectra of the Kepler photometry at 1-minute cadence exhibit a rich and strong set of asteroseismic pulsation modes enabling detailed analysis of the stellar interior. Spectroscopy of the star coupled with asteroseismic modeling of the multiple pulsation modes yield precise measurements of stellar properties, notably Teff = 5793 +/- 74 K, M = 1.079 +/- 0.051 Msun, R = 1.243 +/- 0.019 Rsun, and density 0.7903 +/- 0.0054 (cgs), all measured with fractional uncertainties of only a few percent. Models of Kepler-68b suggest it is likely composed of rock and water, or has a H and He envelope to yield its density of about 3 (cgs)., Comment: 32 pages, 13 figures, Accepted to ApJ

Precise manufacturing of lead foil collimators for gamma-ray imaging is critical to obtain acceptable resolution, sensitivity and uniformity. Actual fabrication poses numerous technical challenges because of the mechanical characteristics of lead foil and the requirement to maintain 50 μm tolerances or better over large areas. This paper describes the materials and techniques used to construct precision one-dimensional parallel and converging slice collimators for a full-ring SPECT imaging system. The methods devised are generally applicable in the construction of similar gamma-ray or X-ray lead foil collimators. Materials used include lead foil with 2% antimony and 0.5% tin, a machinable rigid polymethacrylimide foam and thin film adhesive. A carefully controlled fabrication process was developed to maximize the uniformity of the collimator slices. Sheets of precise thickness foam, adhesive and lead foil were precut and bonded using a heated press. A specially designed vacuum chuck was used for cutting and shaping the slices. Tolerances on foam thickness could be held to 50 μm. Finished slices were stacked together on a surface plate with precut adhesive film placed between each slice. A completed stack of finished slices was heated to bond the entire collimator. Three collimators have been constructed to date. Two are parallel plate collimators, one designed for 140 keV 99mTc gamma rays and one designed for 511 keV annihilation radiation. The third is a converging collimator with 2 : 1 magnification designed for imaging 131I. The measured uniformity and resolution are in good agreement with the design objectives and reflect the variance in the material dimensions. The uniformity varied from 5% standard deviation for the 99mTc collimator to 14% standard deviation for the 131I collimator. The intrinsic resolution varied from 8.5 mm FWHM for the 99mTc parallel collimator to 1.9 mm FWHM for the 131I collimator. The sensitivity of the 99mTc collimator is comparable to current dual head SPECT cameras with LEAP collimators, 670 cpm/μCi. The sensitivity of the 131I converging and 511 keV parallel collimators are an order of magnitude less than that of the 99mTc collimator.

Healthcare gaps, the difference between usual care and best care, are evident in Canada, particularly with respect to our aging, ailing population. Primary care practitioners are challenged to identify, prevent and close care gaps in their practice environment given the competing demands of informed, litigious patients with complex medical needs, ever-evolving scientific evidence with new treatment recommendations across many disciplines and an enhanced emphasis on quality and accountability in healthcare. Patient-centred health and disease management partnerships using measurement, feedback and communication of practice patterns and outcomes have been shown to narrow care gaps. Practice management strategies such as the use of patient registries and recall systems have also been used to help practitioners better understand, follow and proactively manage populations of patients in their practice. The Enhancing Practice to Improve Care project was initiated to determine the impact of a patient-centred health and disease management partnership using practice management strategies to improve patient care and outcomes for patients with chronic kidney disease (CKD). Forty-four general practices from four regions of British Columbia participated and, indeed, demonstrated that care and outcomes for patients with CKD could be improved via the implementation of practice management strategies in a patient-centred partnership measurement model of health and disease management.

The true weighted least-squares (WLS) arrival time estimator for scintillation pulse detection was previously found to out-perform conventional arrival time estimators such as leading-edge and constant-fraction timers, but has limited applications because of its complexity. A new diagonalized version of the weighted least-squares (DWLS) estimator has been developed which, like the true WLS, incorporates the statistical properties of the scintillation detector. The new DWLS reduces estimator complexity at the expense of fundamental timing resolution. The advantage of the DWLS implementation is that only scalar multiplications and additions are needed instead of the matrix operations used in the true WLS. It also preserves the true WLS's ability to effectively separate piled-up pulses. The DWLS estimator has been applied to pulses which approximate the response of BGO and NaI(Tl) scintillation detectors. The timing resolution obtained with the DWLS estimator is then compared to conventional analog timers along with the Cramer-Rao lower bound on achievable timing error. The DWLS out-performs the conventional arrival time estimators but does not provide optimal performance compared to the lower bound; however, it is more robust than the true WLS estimator. >

Didemnin B is a cyclic peptide isolated from the marine tunicate Trididemnin cyanophorum. It is a known potent inhibitor of RNA, DNA and protein synthesis, with activity against the murine B16 melanoma. Fourteen patients with disseminated malignant melanoma were evaluated in a Southwest Oncology Group phase II trial of didemnin B at 4.2 mg/m2 by 30 min i.v. infusion every 28 days (SWOG-8754). Only patients with no prior chemotherapy were eligible; prior radiation therapy, surgery and at most one prior biologic regimen were allowed. Patients with brain metastasis were eligible only if the disease in the brain had been treated and controlled. All patients had to have normal renal and hepatic function and adequate granulocyte and platelet counts, a performance status of 0-2, and bidimensionally measurable disease. Fourteen patients were entered on the study; five received one and nine received two courses of didemnin B. No responses were noted among the 11 patients evaluable for response. Five patients developed unusual but reversible hypersensitivity reactions during the second course of therapy. Other toxicity in this trial was nausea and vomiting and diarrhea, none of severity greater than grade 3. Given the lack of antitumor efficacy and the unusual toxicity, further evaluation of didemnin B in this dose and schedule in malignant melanoma is not warranted.

We report the distribution of planets as a function of planet radius (R_p), orbital period (P), and stellar effective temperature (Teff) for P < 50 day orbits around GK stars. These results are based on the 1,235 planets (formally "planet candidates") from the Kepler mission that include a nearly complete set of detected planets as small as 2 Earth radii (Re). For each of the 156,000 target stars we assess the detectability of planets as a function of R_p and P. We also correct for the geometric probability of transit, R*/a. We consider first stars within the "solar subset" having Teff = 4100-6100 K, logg = 4.0-4.9, and Kepler magnitude Kp < 15 mag. We include only those stars having noise low enough to permit detection of planets down to 2 Re. We count planets in small domains of R_p and P and divide by the included target stars to calculate planet occurrence in each domain. Occurrence of planets varies by more than three orders of magnitude and increases substantially down to the smallest radius (2 Re) and out to the longest orbital period (50 days, ~0.25 AU) in our study. For P < 50 days, the radius distribution is given by a power law, df/dlogR= k R^��. This rapid increase in planet occurrence with decreasing planet size agrees with core-accretion, but disagrees with population synthesis models. We fit occurrence as a function of P to a power law model with an exponential cutoff below a critical period P_0. For smaller planets, P_0 has larger values, suggesting that the "parking distance" for migrating planets moves outward with decreasing planet size. We also measured planet occurrence over Teff = 3600-7100 K, spanning M0 to F2 dwarfs. The occurrence of 2-4 Re planets in the Kepler field increases with decreasing Teff, making these small planets seven times more abundant around cool stars than the hottest stars in our sample. [abridged], Submitted to ApJ, 22 pages, 10 figures

Fundamental method-independent limits on the timing performance of scintillation detectors are useful for identifying regimes in which either present timing methods are nearly optimal or where a considerable performance gain might be realized using better pulse processing techniques. Several types of lower bounds on mean-squared timing error (MSE) performance have been developed and applied to scintillation detectors. The simple Cramer-Rao (CR) bound can be useful in determining the limiting MSE for scintillators having a relatively high rate of photon production such as BaF2 and NaI(Tl); however, it tends to overestimate the achievable performance for scintillators with lower rates such as BGO. For this reason, alternative bounds have been developed using rate-distortion theory [1,2] or by assuming that the conversion of energy to scintillation light must pass through excited states which have exponential lifetime densities [3]. The bounds are functions of the mean scintillation pulse shape, the scintillation intensity, and photodetector characteristics; they are simple to evaluate and can be used to conveniently assess the limiting timing performance of scintillation detectors.

A small animal positron emission tomography (PET) instrument using a high-resolution solid-state detector insert in a conventional PET system was investigated for its potential to achieve sub-millimeter spatial resolution for mouse imaging. Monte Carlo simulations were used to estimate the effect of detector configurations (thickness, length and radius) on sensitivity. From this initial study, a PET system having an inner cylindrical silicon detector (4 cm ID, 4 cm length and 1.6 cm thickness composed of 16 layers of 300 microm x 300 microm x 1 mm pads), for scattering, surrounded by an outer cylindrical BGO scintillation detector (17.6 cm ID, 16 cm length and 2 cm thickness segmented into 3 mm x 3 mm x 20 mm crystals), for capture was evaluated in detail. In order to evaluate spatial resolution, sensitivity and image quality of the PET system, 2D images of multiple point and cylinder sources were reconstructed with the simulation data including blurring from positron range and annihilation photon acollinearity using filtered backprojection (FBP). Simulation results for (18)F demonstrate 340 microm FWHM at the center of the field of view with 1.0% sensitivity from the coincidence of single scattering events in both silicon detectors and 1.0 mm FWHM with 9.0% sensitivity from the coincidence of single scattering in the silicon and full energy absorption of the second photon in the BGO detector.

A very high-resolution small animal positron emission tomograph (PET), which can achieve sub-millimeter spatial resolution, is being developed using silicon pad detectors. The prototype PET for a single slice instrument consists of two 1 mm thick silicon pad detectors, each containing a 32×16 array of 1.4×1.4 mm pads readout with four VATAGP3 chips which have 128 channels low-noise self-triggering ASIC in each chip, coincidence units, a source turntable and tungsten slice collimator. The silicon detectors were located edgewise on opposite sides of a 4 cm field-of-view to maximize efficiency. Energy resolution is dominated by electronic noise, which is 0.98% (1.38 keV) FWHM at 140.5 keV. Coincidence timing resolution is 82.1 ns FWHM and coincidence efficiency was measured to be 1.04×10 −3 % from two silicon detectors with annihilation photons of 18 F source. Image data were acquired and reconstructed using conventional 2-D filtered-back projection (FBP) and a maximum likelihood expectation maximization (ML-EM) method. Image resolution of approximately 1.45 mm FWHM is obtained from 1-D profile of 1.1 mm diameter 18 F line source image. Even better resolution can be obtained with smaller detector element sizes. While many challenges remain in scaling up the instrument to useful efficiency including densely packed detectors and significantly improved timing resolution, performance of the test setup in terms of easily achieving sub-millimeter resolution is compelling.

This study reports on a spectral monitoring method in which (1) a small source fixed to the camera is used, (2) a narrow, offset window is set on the side of the photopeak, and (3) variations in count rate are measured to assess energy shifts in the vicinity of the source. For one camera model, the count rate drops from 100% to 76% over a rotation of 180°, implying a local energy shift of 1.4 keV. Also looked for are local count‐rate variations with rotation for (1) wide‐symmetric, (2) 20%‐symmetric, and (3) 10%‐asymmetric windows. The last is in limited use to partially compensate for Compton scattering. The effects of background and time stability are assessed.

This 1990 symposium was the seventh in a series of meetings which began in 1964. The 300 participants from 23 countries and the 65 oral and 77 poster presentations were more than double the size of the 1985 symposium. Some of this increase derived from the broadened scope of the program. Previous meetings emphasized X-rays and gamma-rays, but it has been increasingly clear that distinction from other forms of radiation (i.e., electrons, alpha-particles and neutrons) was contrived. This broadening led to papers in fields such as airport'' monitors and arms control. However, most of the increase in size of the symposium is simply a reflection of the vigorous activity, both academic and industrial in radiation measurements and their many applications. The papers in these Proceedings are arranged by major topic without regard to whether the paper was invited or contributed, oral or poster. Discussion, although an important part of the meeting, was not recorded and therefore is not included in the Proceedings.

In single photon emission nuclear medicine, computed tomography systems that employ only a limited angular range of projection data suffer from blurring in the depth (or z) direction. With simulated, data, we show that including a second set of projections taken in an orthogonal direction sharpens the image in the z direction. For heart applications, this sharpening improves the sizing of a simulated 2 cm diameter "hot" infarct by 39%. It also should improve the contrast of "cold" infarcts by eliminating blurring from other planes, but here we have found a complication, in that, with the present approximate algorithm, effects from the lack of symmetry in two-view tomography may overshadow benefits from contrast improvement. Further simulation study is called for.

HE impact of computers on Nuclear Cardiology and the progress which has been made through computer applications is perhaps best illustrated by several historical observations. First, it is of note that all clinically important types of nuclear cardiologic procedures were initially performed without the aid of a computer. For example, the first gated equilibrium, blood pool ventriculograms performed by Zaret et al.‘** were accomplished by analog imaging. A physiologic trigger or gate was used to turn the gamma camera image recording system on and off to define “end systole” and “end diastole” which were the only two images obtained. The gating “window” used for end diastole was the 60-msec interval immediately prior to the Rwave. For end systole, data were recorded during the T-wave. Quantitative analysis was then accomplished manually. The analog images were projected to life size and the ventricular borders traced by hand. Ventricular volumes and ejection fractions were calculated using area length formulae adapted from contrast angiography. The data obtained in this fashion correlated well with results from contrast angiography and provided a strong motivation for further technical development. Likewise, in early applications of the first pass technique, computers were not used. Rather, data were recorded on video tape for subsequent replay and analysis.3 These analog imaging techniques were extremely time consuming, particularly for purposes of quantitative analysis, took advantage of only a small fraction of the potentially available data, and provided limited visual appreciation of cardiac dynamics. The first logical adaptation of the computer to radionuclide ventriculography was simply to acquire the gated end diastolic and end systolic frames into computer memory, instead of onto film, one frame at a time. Initially the data analysis was again performed by hand by tracing ventricular contours on the computer screen. As before, this analytic approach was quite tedious and partly for this reason very little clinical use was made of radionuclide ventriculography, initially. However, several breakthroughs in computer techniques occurred in the early 1970s which established radionuclide ventriculography as a feasible clinical procedure. First, Seeker-Walker and Parker4,’ recognized that after equilibration in the blood pool the net ventricular count rate resulting from an intravascular tracer (e.g., Tc-99m albumin or Tc-99m RBC) at any time in the cardiac cycle is proportional to ventricular blood volume. This germinal observation permits calculation of the ventricular ejection fraction and other quantitative parameters through analysis of net counts (i.e., background corrected) in the ventricles (a task for which the computer is uniquely suited) rather than by the more laborious geometric technique. The formula for the count based ejection fraction is

Maximum likelihood (ML) estimators offer advantages of improved spatial resolution and linearity over traditional position estimates in position sensitive detectors. We have constructed a two board, multibus based hybrid position computer capable of performing the ML estimate at SPECT countrates. In addition, the board can implement any estimate linear in the photomultiplier tube outputs.

A new emission computed tomographic reconstruction technique has been developed. Each projection is fit with an arbitrary functional form which is constrained in shape by the sharpest response which can be obtained in a tomograph. The image is then reconstructed by backprojecting the best estimate projections which have been filtered by a ramp function in the frequency domain. This procedure reduces the variance in image pixel values while maintaining resolution which is near the intrinsic resolution of the tomograph. This paper presents results for both measured and simulated data from a tomograph designed to measure annihilation photons from the decay of positrons.

Monte-Carlo methods have been applied to the design of a detector suitable for use in a SPECT cylindrically shaped scintillation camera. Included in the study are the calculated detection characteristics of two scintillator materials and the optical performance of several geometric configurations. Results include maps of the light distribution for several rectangular crystal-light guide combinations, a comparison of various approaches to specifying the optical properties of detector surfaces, and estimates of relative light output for various geometries.

The lack of a pituitary imaging agent combined with the considerable clinical value for such an agent prompted an examination of 3H-spiroperidol (3HSp). Spiroperidol was selected for initial evaluation based on its high affinity for D2 receptors which are known to be present in the pituitary. A time course study of 3HSp concentration in rat pituitary and other tissues was conducted. Pituitary activity levels were found to be constant from 5 min to 4 h and were about 8 times levels in corpus striatum at 1 h. Blocking studies with (+) butaclamol and with unlabelled spiroperidol suggested the existence of both a D2 receptor mediated binding localization and a second uptake which is postulated to be an internalization process. Further studies involving ultracentrifugation of pituitary homogenates resulted in evidence for association of 3HSp with dense subcellular particles. 3HSp thus appears to be internalized by pituitary cells.

Historically in nuclear medicine the acceptance window for total-energy pulse-height has been set to maximize contrast and resolution in the image. Recently, there has been increased emphasis on quantification of digital images to calculate, for example, left ventricular volume or tumor radiation absorbed dose. In this paper, we consider specifically what improvements can be made in emission computed tomography simply by employing a window which is offset to the high-energy side of the photopeak in order to reduce the contribution of Compton scattered gamma-rays. The window is offset so as to reduce the count rate for a source in air by 20%. Two lucite phantoms were measured. One was a short cylinder filled with a uniformly-distributed solution of 99mTc in water. The other was a head phantom with a 0.6 cm 3 "tumor" containing 99mTc. Water surrounding the tumor could be nonradioactive or contain a dilute background activity. Absolute calibration was accomplished by imaging the simulated tumor in the air-filled phantom. With the offset window, calculated tumor activity is only 3% and 7% high without and with background respectively compared to 20% and 26% high with the symmetric window. However, total activity of the entire slice is still 37% high even without background. For the cylinder containing uniform activity, the error in specific activity drops from 30% to 18% with the offset window. Therefore, an asymmetric window significantly improves quantification, and for certain cases such as an isolated tumor, may be sufficiently accurate without further correction.

The utility of ω-123I-hexadecanoic acid myocardial scintigraphy as a metabolic probe of cardiomyopathies was investigated. Sixteen patients with a variety of cardiomyopathies and myopathies that involve cardiac muscle and ten volunteers were imaged in the postabsorptive state in a 40° LAO projection after a standard dose of ω-123I-hexadecanoic acid. An elimination T1/2 was calculated from the left ventricular myocardial time-activity curve. An uptake index, corrected for chest wall attenuation, was also computed in 7 of 10 volunteers and 8 of 16 patients. Of the 16 patients, only 2 had distinctly abnormal ω-123I-hexadecanoic acid myocardial tracer kinetics. The first patient had a metabolic disorder of which cartine deficiency was one component. The second patient had endocardial fibroelastosis, a process which has been linked to disorders which deprive the myocardium of oxygen and energy. Therefore, the cardiomyopathy may have been caused by some abnormality of cardiac metabolism other than carnitine deficiency. Although of limited utility in the overall cardiomyopathic population, ω-123I-hexadecanoic acid myocardial scintigraphy should be further investigated as a screening test for carnitine deficiency and related metabolic abnormalities in patients at risk.