What is the best way of delivering virtual nature for improving mood? An experimental comparison of high definition TV, 360° video, and computer generated virtual reality.

Exposure to 'real' nature can increase positive affect and decrease negative affect, but direct access is not always possible, e.g. for people in health/care settings who often experience chronic boredom. In these settings 'virtual' forms of nature may also have mood-related benefits (e.g. reducing boredom) but it has been difficult to separate effects of nature content from those of delivery mode. The present laboratory-based study explored whether exposure to three different delivery modes of virtual nature could reduce negative affect (including boredom) and/or increase positive affect. Adult volunteer participants (n = 96) took part in a boredom induction task (to simulate the emotional state of many people in health/care settings) before being randomly assigned to view/interact with a virtual underwater coral reef in one of three experimental conditions: (a) 2D video viewed on a high-definition TV screen; (b) 3600 video VR (360-VR) viewed via a head mounted display (HMD); or (c) interactive computer-generated VR (CG-VR), also viewed via a HMD and interacted with using a hand-held controller. Visual and auditory content was closely matched across conditions with help from the BBC's Blue Planet II series team. Supporting predictions, virtual exposure to a coral reef reduced boredom and negative affect and increased positive affect and nature connectedness. Although reductions in boredom and negative affect were similar across all three conditions, CG-VR was associated with significantly greater improvements in positive affect than TV, which were mediated by greater experienced presence and increases in nature connectedness. Results improve our understanding of the importance of virtual nature delivery mode and will inform studies in real care settings.

Recreational physical activity in natural environments and implications for health: A population based cross-sectional study in England.

BACKGROUND: Building on evidence that natural environments (e.g. parks, woodlands, beaches) are key locations for physical activity, we estimated the total annual amount of adult recreational physical activity in England's natural environments, and assessed implications for population health. METHODS: A cross-sectional analysis of six waves (2009/10-2014/5) of the nationally representative, Monitor of Engagement with the Natural Environment survey (n=280,790). The survey uses a weekly quota sample, and population weights, to estimate nature visit frequency across England, and provides details on a single, randomly selected visit (n=112,422), including: a) duration; b) activity; and c) environment type. RESULTS: Approximately 8.23 million (95% CIs: 7.93, 8.54) adults (19.5% of the population) made at least one 'active visit' (i.e. ≥30min, ≥3 METs) to natural environments in the previous week, resulting in 1.23 billion (1.14, 1.32) 'active visits' annually. An estimated 3.20 million (3.05, 3.35) of these also reported meeting recommended physical activity guidelines (i.e. ≥5×30min a week) fully, or in part, through such visits. Active visits by this group were associated with an estimated 109,164 (101,736, 116,592) Quality Adjusted Life Years (QALYs) annually. Assuming the social value of a QALY to be £20,000, the annual value of these visits was approximately £2.18 billion (£2.03, £2.33). Results for walking were replicated using WHO's Health Economic Assessment Tool. CONCLUSIONS: Natural environments provide the context for a large proportion of England's recreational physical activity and highlight the need to protect and manage such environments for health purposes.

Coastal climate is associated with elevated solar irradiance and higher 25(OH)D level.

INTRODUCTION: There is evidence that populations living close to the coast have improved health and wellbeing. Coastal environments are linked to promotion of physical activity through provision of safe, opportune, aesthetic and accessible spaces for recreation. Exposure to coastal environments may also reduce stress and induce positive mood. We hypothesised that coastal climate may influence the vitamin D status of residents and thus partly explain benefits to health. MATERIALS AND METHODS: Ecological and cross-sectional analyses were designed to elucidate the connection between coastal residence and vitamin D status. We divided residential data, from developed land use areas and the Lower Super Output Areas or Data Zones (Scotland) of the 1958 Birth Cohort participants, into the following coastal bands: <1 km, 1-5 km, 5-20 km, 20-50 km and over 50 km. In the ecological analysis we used a multiple regression model to describe the relationship between UV vitd and coastal proximity adjusted for latitude. Subsequently, using the residential information of the participants of the 1958 Birth Cohort we developed a multiple regression model to understand the relationship between serum 25(OH)D (a marker of vitamin D status) and coastal proximity adjusted for several factors related to vitamin D status (e.g. diet, outdoor activity). RESULTS: We found that coastal proximity was associated with solar irradiance; on average a 99.6 (96.1-103.3)J/m(2)/day regression coefficient was recorded for settlements <1 km from the coast compared with those at >50 km. This relationship was modified by latitude with settlements at a lower latitude exhibiting a greater effect. Individuals living closer to the coast in England had higher vitamin D levels than those inland, particularly in autumn. CONCLUSION: Geographic location may influence biochemistry and health outcomes due to environmental factors. This can provide benefits in terms of vitamin D status but may also pose a risk due to higher skin cancer risk. We provide further evidence in support of the claim that coastal environments can provide opportunities for health and wellbeing.

Changes in quantitative ultrasound in infants born at less than 32 weeks' gestation over the first 2 years of life: influence of clinical and biochemical changes.

Studies in preterm infants show reduced speed of sound (SOS) as measured by quantitative ultrasound (QUS) during the immediate neonatal period. There is a scarcity of data on SOS changes following hospital discharge. The aim of this study was to assess SOS over the first 2 years in preterm infants. Infants were recruited from a neonatal follow-up clinic. Tibial QUS was performed using the Omnisense 7000P scanner. Thirty-nine infants born at <32 weeks' gestation had a single SOS measurement (median 3,203 m/second, range 2,609-3,495) which correlated with corrected gestational age (CGA) (r = 0.8, P < 0.005). The majority of measurements were within the manufacturer's reference range for term infants. SOS standard deviation score (SDS) in infants aged 0-6 months CGA demonstrated a negative correlation with duration of total parenteral nutrition (r = 0.7, P < 0.05) and a positive correlation with serum phosphate (r = 0.6, P < 0.05.) Two groups of infants had serial measurements: eight had measurements performed at term CGA and early infancy (early) and seven had measurements in later infancy (late). In the early group SOS SDS increased (P < 0.005), and the greatest increase in SOS over time occurred in infants with the lowest SOS at term (r = 0.9). In the late group there was no significant change over time. SOS SDS change did not show any correlation to weight SDS change. Catch-up in SOS occurs postterm in most infants by 6 months and is independent of postnatal growth. Infants with the lowest SOS at term have the fastest rate of catch-up. The opportunity for catch-up may be greatest in early infancy.

Rate of referral of breech infants for hip ultrasound: an audit cycle.

BACKGROUND: Infants with risk factors for developmental dysplasia of the hip (DDH) should have hip ultrasounds performed shortly after birth to detect and treat the condition at an early stage. Breech presentation is associated with increased risk of DDH. We embarked on an audit cycle to assess and improve our rate of referral of breech infants for hip ultrasound. METHODS: Two retrospective audits (phases I and II) were carried out before, and after, the introduction of a new pro-forma which encouraged recognition of breech presentation at the time of the routine neonatal examination. Breech infants were identified from labour ward records. Multiple births and infants < 35 weeks gestation were excluded. Infants were considered to have been referred for ultrasound if the computer system at our affiliated children's hospital held a record of an ultrasound appointment. RESULTS AND CONCLUSIONS: In phase I 56% of breech infants born in our hospital had been referred for hip ultrasound. In phase II the referral rate had risen to 76% (p = 0.034). We conclude that the change in practice was effective. Further improvement might be achieved by increasing staff awareness of risk factors for DDH and by enlisting the help of advanced neonatal nurse practitioners (ANNPs) in routine neonatal examinations.

Longitudinal changes in bone health as assessed by the speed of sound in very low birth weight preterm infants.

OBJECTIVE: To assess longitudinal changes in speed of sound (SOS) in very low birth weight (VLBW) infants and investigate the relationship with markers of osteopathy of prematurity (OP) and clinical illness. STUDY DESIGN: Twenty-five infants were recruited. Eighteen infants, median gestation 27 weeks (range 24-32), median birth weight 957 g (range 625-1500 g), had serial scans. SOS was measured at both tibiae weekly until 35 to 37 weeks corrected gestational age (CGA). RESULTS: Initial median SOS standard deviation score (SDS) (Z) score was -0.07 (range-1.3-1.3). SOS correlated with gestation (r, 0.8, P<.005), and birth weight (r, 0.67, P<.005.) SOS fell from a median of 2923 m/s (2672-3107) at birth to 2802 m/s (2502-2991) at 35 to 37 weeks CGA (P<.05). This fall was greater in the 24- to 27-week gestation cohort with a median reduction of 2.2 SDS (1.6, 4.0) compared with 1.3 SDS (0.8-2.2) in those>28 weeks (P<.05). There was a negative correlation between SOS, at the end of the study, peak serum alkaline phosphatase (ALP) (r, 0.6, P<.05), CRIB (Clinical Risk Index for Babies)/CRIB II scores (both r, 0.6, P<.05), and duration of total parenteral nutrition (TPN) (r, 0.58, P<.05.) CONCLUSIONS: Although tibial SOS was within the expected range at birth, there was a subsequent failure to gain SOS, and this was most marked in infants of a lower gestation.

Neonatal nephrocalcinosis: long term follow up.

AIMS: To assess the spontaneous resolution of neonatal nephrocalcinosis and its long term effects on renal function. METHODS: Fourteen very low birthweight preterm babies with nephrocalcinosis were followed up at 5-7 years of age; 14 controls were matched for sex, gestation, and birth weight. Height, weight, blood pressure, and renal symptomatology were recorded, and a renal ultrasound scan was performed. Early morning urine osmolality and creatinine ratios of albumin, phosphate, calcium, oxalate and beta microglobulin were determined. Urea and electrolytes in the study group were determined, and glomerular filtration rate (GFR) and TmP/GFR (tubular reabsorption of phosphate per GFR) were calculated. Statistical analysis was performed on a group basis using the Mann-Whitney confidence interval. RESULTS: Mean age was 6.9 years (range 5.81-7.68). An early morning urine osmolality >700 mOsm/kg was achieved in all cases. In two cases and four controls, the calcium/creatinine ratio was >0.7 mmol/mmol. In all cases, the GFR was normal (median 132.6 ml/min/1.73 m(2) (range 104.1-173.1)). Median TmP/GFR was 1.22 mmol/l (0.73-1.61), with two having levels below the normal range. These did not have persisting nephrocalcinosis. Nephrocalcinosis was found in three of the 12 cases scanned and one control. There were no significant differences in urine biochemistry. CONCLUSIONS: Resolution of nephrocalcinosis occurred in 75% of cases. No evidence was found to suggest that nephrocalcinosis is associated with renal dysfunction in the long term. There was evidence of hypercalciuria in the cases and controls, suggesting that prematurity may be a risk factor.

Quantitative ultrasound assessment of bone in preterm and term neonates.

There is a need to explore novel methods of assessing bone health in sick preterm infants. This study of the speed of sound in the long bones of newborn term and preterm infants shows that, in this population, this technique is not site specific and has a high degree of interobserver and intraobserver precision. The speed of sound in newborn infants is primarily dependent on gestation rather than birth weight.

Nephrocalcinosis in preterm babies.

OBJECTIVES: To determine prospectively the incidence and cause of nephrocalcinosis in preterm infants. STUDY DESIGN: Inborn babies of gestation less than 32 weeks or birth weight less than 1500 g were eligible to be entered into a prospective observational study. Two renal ultrasound scans were performed, the first at 1 month postnatal age and the second at term or discharge. Data were collected on gestation, birth weight, sex, race, family history of renal calculi, oliguria on first day, respiratory support (ventilation, steroid, and oxygen dependency), and use of nephrotoxic drugs (gentamicin, vancomycin, and frusemide). Intake of fluid, calcium, and phosphate and plasma urea, creatinine, calcium, and phosphate were recorded for the first 6 weeks of life. Random urinary calcium/creatinine, oxalate/creatinine, and urate/creatinine ratios and tubular absorption of phosphate were measured once at term. RESULTS: A total of 101 preterm infants were studied. Twenty three (23%) had abnormal ultrasound scans. Sixteen (16%) had nephrocalcinosis. On univariate analysis, gestational age, male sex, duration of ventilation, oxygen dependency, duration and frequency of gentamicin treatment, toxic gentamicin/vancomycin levels, and postnatal dexamethasone were significantly associated with nephrocalcinosis. In addition, babies with nephrocalcinosis had a lower intake of fluid, calcium, and phosphate, longer duration of total parenteral nutrition, and higher urinary oxalate/creatinine and urate/creatinine ratios than infants who did not have the condition. There was also a significant association with plasma urea and creatinine but not with plasma calcium or phosphate or urinary calcium. Multivariate analysis showed that the strongest predictors of nephrocalcinosis were duration of ventilation, toxic gentamicin/vancomycin levels, low fluid intake, and male sex. CONCLUSION: 16% of babies born at less than 32 weeks gestation developed nephrocalcinosis. The multifactorial origin, in particular, the association with extreme prematurity and severity of respiratory disease, is confirmed. In addition, an association with male sex, frequency and duration of gentamicin use, and high urinary oxalate and urate excretion is shown.

Comparison of electrocardiographic-gated technetium-99m sestamibi single-photon emission computed tomographic imaging and rest-redistribution thallium-201 in the prediction of myocardial viability.

Although the combined assessment of perfusion and function using rest electrocardiographic (ECG)-gated technetium-99m (Tc-99m) sestamibi single-photon emission computed tomographic (SPECT) imaging has been shown to improve sensitivity and accuracy over perfusion alone in the prediction of myocardial viability, no data are available comparing this technique with rest-redistribution thallium-201. Thirty patients with coronary artery disease and left ventricular dysfunction (ejection fraction < or = 40%) underwent rest-redistribution thallium-201 and rest ECG-gated Tc-99m sestamibi SPECT imaging before revascularization and rest ECG-gated Tc-99m sestamibi SPECT imaging at 1 or 6 weeks after revascularization. All thallium-201 and Tc-99m sestamibi images were interpreted by a consensus agreement of 3 experienced readers without knowledge of patient identity or time of imaging with Tc-99m sestamibi (before or after revascularization) using a 17-segment model. Concordance between techniques for the prediction of viability was 89% (kappa 0.556 +/- 0.109). With rest-redistribution thallium-201, sensitivity, specificity, positive predictive value, negative predictive value, and predictive accuracy were 95%, 59%, 88%, 78%, and 86%, respectively. With rest ECG-gated Tc-99m sestamibi SPECT imaging, sensitivity, specificity, positive predictive value, negative predictive value, and predictive accuracy were 96%, 55%, 87%, 80%, and 86%, respectively (p = NS vs rest-redistribution thallium-201). Although both techniques are comparable for detecting viable myocardium, rest ECG-gated Tc-99m sestamibi SPECT imaging allows direct assessment of both myocardial perfusion and ventricular function, which may be clinically useful in patients who require assessment of myocardial viability.

Impact of limited treadmill exercise on adenosine Tc-99m sestamibi single-photon emission computed tomographic myocardial perfusion imaging in coronary artery disease.

Limited exercise combined with dipyridamole increases myocardial perfusion defect severity compared with dipyridamole alone. The impact of limited exercise combined with adenosine on myocardial perfusion defect severity is unknown. This study compares myocardial perfusion defect severity with adenosine alone and adenosine combined with limited exercise. Thirty-two patients with coronary artery disease underwent on separate days and in randomized order technetium-99m sestamibi (25 to 30 mCi) single-photon emission computed tomographic imaging at rest, after adenosine (140 microg/kg/min x 6 minutes), and after adenosine (140 microg/kg/min x 4 minutes) during 6 minutes of modified Bruce treadmill exercise (adenosine-exercise). Radiopharmaceutical was injected at 3 and 5 minutes during adenosine and adenosine-exercise, respectively. Images were interpreted by a consensus agreement of 3 nuclear cardiologists without knowledge of patient identity, stress protocol, or clinical data using a 17-segment model and 5-point scoring system. A summed stress score (SSS), summed rest score (SRS), and summed difference (SSS-SRS) score (SDS) were calculated for each image. Peak stress heart rate and rate-pressure product were higher for adenosine-exercise than adenosine (102 +/- 19 vs 81 +/- 11 beats/min and 13,972 +/- 4,265 vs 10,623 +/- 2,131, respectively; both p <0.001). Sensitivity for detection of > or = 50% coronary stenosis was 75% and 72% for adenosine-exercise and adenosine, respectively (p = NS). There were no differences in SSS and SDS between adenosine-exercise and adenosine (8.2 +/- 5.9 vs 8.1 +/- 6.3 and 4.9 +/- 4.1 vs 5.2 +/- 4.6, respectively; both p = NS). Thus, in patients with coronary artery disease, limited treadmill exercise combined with adenosine does not increase myocardial perfusion defect severity compared with standard adenosine technetium-99m sestamibi single-photon emission computed tomographic myocardial perfusion imaging.

Comparison of exercise, dipyridamole, adenosine, and dobutamine stress with the use of Tc-99m tetrofosmin tomographic imaging.

PURPOSE: The purpose of this study was to compare defect extent and severity and myocardial uptake with exercise and pharmacologic stress with technetium-99m (Tc-99m) tetrofosmin tomographic myocardial perfusion imaging. BACKGROUND: Detection of stress-induced myocardial perfusion defects depends on both a disparity in blood flow between normal and stenotic vessels and the extraction fraction and linearity of myocardial uptake of the tracer. There are limited clinical data for exercise or pharmacologic stress with Tc-99m tetrofosmin tomographic myocardial perfusion imaging. METHODS: Thirty-one patients with coronary artery disease and 7 with a < 5% likelihood of coronary artery disease underwent on separate days Tc-99m tetrofosmin single-photon emission computed tomographic imaging at rest and after exercise, dipyridamole, adenosine, and dobutamine stress. Images were interpreted by a blinded consensus of 3 experienced readers with a 17-segment model and 5-point scoring system. RESULTS: Compared with exercise, the summed stress score was smaller with dipyridamole (P < .01), and the reversibility score was smaller with both dipyridamole (P < .01) and dobutamine (P < .05), whereas the number of abnormal and reversible segments was less with both dipyridamole (P < .01 and P < .001, respectively) and dobutamine (both P < .05). No significant differences were found in the summed stress or reversibility scores and the number of abnormal or reversible segments between exercise and adenosine. CONCLUSIONS: Compared with exercise, defect extent, severity, and reversibility are less with dipyridamole and dobutamine with Tc-99m tetrofosmin single photon emission computed tomographic imaging.

Light-emitting diodes and cool white fluorescent light similarly suppress pineal gland melatonin and maintain retinal function and morphology in the rat.

BACKGROUND AND PURPOSE: A novel light-emitting diode (LED) light source for use in animal-habitat lighting was evaluated. METHODS: The LED was evaluated by comparing its effectiveness with that of cool white fluorescent light (CWF) in suppressing pineal gland melatonin content and maintaining normal retinal physiology, as evaluated by use of electroretinography (ERG), and morphology. RESULTS: Pineal melatonin concentration was equally suppressed by LED and CWF light at five light illuminances (100, 40, 10, 1, and 0.1 lux). There were no significant differences in melatonin suppression between LED and CWF light, compared with values for unexposed controls. There were no differences in ERG a-wave implicit times and amplitudes or b-wave implicit times and amplitudes between 100-lux LED-exposed rats and 100-lux CWF-exposed rats. Results of retinal histologic examination indicated no differences in retinal thickness, rod outer segment length, and number of rod nuclei between rats exposed to 100-lux LED and 100-lux CWF for 14 days. Furthermore, in all eyes, the retinal pigmented epithelium was intact and not vacuolated, whereas rod outer segments were of normal thickness. CONCLUSION: LED light does not cause retinal damage and can suppress pineal melatonin content at intensities similar to CWF light intensities.

Influence of arm positioning on rest/stress technetium-99m labeled sestamibi tomographic myocardial perfusion imaging.

BACKGROUND: Single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is routinely performed with patients' arms positioned above their heads to avoid potential attenuation artifact and reduced image quality. Currently no data are available to support the use of this practice using 99mTc SPECT MPI: METHODS AND RESULTS: Forty-one patients referred for routine rest/stress MPI were imaged using the standard protocol with arms positioned above their heads and again with their arms at their sides. The patients were injected with 10 to 45 mCi (370 to 1665 MBq) of 99mTc-labeled sestamibi (99mTc-sestamibi), and SPECT images were acquired 30 to 90 minutes later. Thirty patients were imaged on an ADAC Vertex dual-head camera and 11 patients on an ADAC Cirrus single-head camera. Images were interpreted by 3 nuclear cardiologists without knowledge of patient identity, arm position, or camera type using a 17-segment scoring model. No significant differences were noted in the percentage of abnormal study results, reversibility extent, or location of MPI defects between the 2 arm positions in the same patients. Image quality was also similar. CONCLUSION: Arm positioning does not influence the interpretation of 99mTc-sestamibi SPECT myocardial perfusion imaging with regard to image quality or defect location and extent.

Functional assessment with electrocardiographic gated single-photon emission computed tomography improves the ability of technetium-99m sestamibi myocardial perfusion imaging to predict myocardial viability in patients undergoing revascularization.

This study evaluates the use of electrocardiographic (ECG) gated single-photon emission computed tomographic (SPECT) myocardial perfusion imaging for the prediction of viability in patients undergoing revascularization, who have coronary disease and left ventricular dysfunction. Fifty patients underwent technectium-99m (Tc-99m) sestamibi ECG gated SPECT imaging preoperatively at rest and 1 week after revascularization, whereas 36 (72%) also underwent imaging 6 weeks after revascularization. Images were interpreted by the consensus of 3 experienced readers without knowledge of patient identity or time of imaging (pre- or postrevascularization) for perfusion and wall motion using a 17-segment model. Results of perfusion alone were compared with perfusion and wall motion combined. One hundred five coronary artery territories were revascularized, 96 of which were viable and 9 nonviable. Perfusion alone predicted 87 to be viable and 18 nonviable (sensitivity 86%, specificity 55%, positive predictive value 95%, negative predictive value 28%, and overall accuracy 85%). Perfusion and wall motion combined identified 95 territories to be viable (sensitivity 95%; p <0.025; specificity 55%, positive predictive value 96%, negative predictive value 50%, and overall accuracy 91%; p <0.05). Thus, Tc-99m sestamibi ECG gated SPECT myocardial perfusion imaging at rest allows assessment of both perfusion and wall motion, which significantly improves the sensitivity and overall accuracy for determination of viability in comparison with perfusion alone.

Fasting and nonfasting iodine-123-idophenylpentadecanoic acid myocardial SPECT imaging in coronary artery disease.

UNLABELLED: Iodine-123-labeled idophenylpentadecanoic acid (IPPA) metabolic imaging has been shown to be clinically useful for the identification of myocardial viability in patients with coronary artery disease and left ventricular dysfunction. Imaging is usually performed under fasting conditions since nonfasting conditions may affect myocardial uptake of 123I-IPPA. The purpose of this study was to examine the impact of dietary condition on 123I-IPPA metabolic imaging. METHODS: Forty patients with stable coronary artery disease underwent, in randomized order and on separate days, 123I-IPPA SPECT myocardial imaging under fasting and nonfasting conditions. Patients were injected with 123I-IPPA (4-5 mCi) at rest with imaging performed at 4 (initial) and 30 (delay) min. For each image (initial and delay images), 10 segments were analyzed by three experienced observers without knowledge of patient identity or dietary condition using a 5-point grading system (O = no uptake to 4 = normal uptake). A summed global score was obtained for each image by adding the scores for all 10 segments. Image quality was assessed using a 3-point grading system. RESULTS: Visual agreement for normal and abnormal segments between fasting and nonfasting conditions was 82% (kappa = 0.63). There were no significant differences in the summed global scores for both conditions. Image quality was equivalent for both conditions in 65% of cases and superior under the nonfasting condition in 25% of cases. CONCLUSION: Image quality as well as the presence, location and severity of defects are similar under fasting and nonfasting conditions with 123I-IPPA. Therefore, fasting is not necessary before 123I-IPPA SPECT imaging for the assessment of myocardial viability.

Effect of time on liver clearance of technetium-99m-tetrofosmin in patients with acute chest pain: when should imaging begin?

OBJECTIVE: Due to stable myocardial retention and technetium imaging characteristics, 99mTc-tetrofosmin has been considered potentially useful for acute chest pain imaging. Tetrofosmin also has favorable biokinetics with reported rapid liver clearance, 5 min poststress and 30-45 min post-rest injection. Since comparable data are not available, the effect of time on liver clearance was evaluated in patients with acute chest pain. METHODS: One hundred six patients received an intravenous injection of 25-30 mCi 99mTc-tetrofosmin to evaluate acute chest pain. SPECT imaging was performed 15-120 min after injection of the tracer. Patient images were grouped according to the time of acquisition after acute injection: 15-30 min, 31-45 min, 46-60 min, 61-90 min and > 90 min. Quantitative analysis was performed of a similar anterior projection for each patient consisting of 6 X 6-pixel region of interest over the myocardium and adjacent liver. Average counts per pixel were determined and a heart/liver (H/Li) ratio was calculated. RESULTS: The mean H/Li ratio was < 1.0 for patient images acquired 15-45 min after injection, and > 1.0 for patient images acquired after 45 min. The difference was statistically significant (p < 0.05). CONCLUSION: Quantitative analysis suggests that the optimal imaging time should be at least 45 min after the injection of 99mTc-tetrofosmin to allow adequate liver clearance before image acquisition of acute chest pain syndromes.