Variability in PET image quality and quantification measured with a permanently filled 68Ge-phantom: a multi-center study

BACKGROUND

This study evaluated, as a snapshot, the variability in quantification and image quality (IQ) of the clinically utilized PET [¹⁸F]FDG whole-body protocols in Finland using a NEMA/IEC IQ phantom permanently filled with ⁶⁸Ge.

METHODS

The phantom was imaged on 14 PET-CT scanners, including a variety of models from two major vendors. The variability of the recovery coefficients (RC_max, RC_mean and RC_peak) of the hot spheres as well as percent background variability (PBV), coefficient of variation of the background (COV_BG) and accuracy of corrections (AOC) were studied using images from clinical and standardized protocols with 20 repeated measurements. The ranges of the RCs were also compared to the limits of the EARL ¹⁸F standards 2 accreditation (EARL2). The impact of image noise on these parameters was studied using averaged images (AVIs).

RESULTS

The largest variability in RC values of the routine protocols was found for the RC_max with a range of 68% and with 10% intra-scanner variability, decreasing to 36% when excluding protocols with suspected cross-calibration failure or without point-spread-function (PSF) correction. The RC ranges of individual hot spheres in routine or standardized protocols or AVIs fulfilled the EARL2 ranges with two minor exceptions, but fulfilling the exact EARL2 limits for all hot spheres was variable. RC_peak was less dependent on averaging and reconstruction parameters than RC_max and RC_mean. The PBV, COV_BG and AOC varied between 2.3-11.8%, 9.6-17.8% and 4.8-32.0%, respectively, for the routine protocols. The RC ranges, PBV and COV_BG were decreased when using AVIs. With AOC, when excluding routine protocols without PSF correction, the maximum value dropped to 15.5%.

CONCLUSION

The maximum variability of the RC values for the [¹⁸F]FDG whole-body protocols was about 60%. The RC ranges of properly cross-calibrated scanners with PSF correction fitted to the EARL2 RC ranges for individual sphere sizes, but fulfilling the exact RC limits would have needed further optimization. RC_peak was the most robust RC measure. Besides COV_BG, also RCs and PVB were sensitive to image noise.

Propranolol increases the complexity of heart rate fluctuations--a mode of antiarrhythmic action?

OBJECTIVE

To study the beta-blocking effect of propranolol on heart rate and arterial blood pressure fluctuations in healthy subjects using linear methods and a set of nonlinear models.

METHODS

In a randomized, double-blind, placebo-controlled study, healthy young adults received a 40 mg oral dose of propranolol (n = 12) or placebo (n = 12). The effects of propranolol and placebo were assessed using time series of the RR interval (RRI) and systolic arterial blood pressure (SAP) obtained from continuous ECG and blood pressure signal recordings. Heart rate and systolic arterial blood pressure fluctuations were analyzed using nonlinear and linear methods of time series statistics.

RESULTS

Propranolol significantly increased the complexity of heart rate fluctuations in terms of symbol dynamic (SymDyn) entropy and symbol dynamic percentage of forbidden words. Propranolol augmented cross entropy between RRI and SAP and increased fractal dimension of RRI. beta-blockade also affected linear measures of RRI fluctuations by increasing parasympathetic, respiration-related high-frequency (HF) variability and arterial baroreflex-related low-frequency (LF) variability. Propranolol administration, however, had no effect on the complexity of SAP fluctuations assessed using nonlinear time series statistics.

CONCLUSIONS

beta-blockade by propranolol has a differential effect on RRI and SAP fluctuations in healthy subjects. Propranolol increases the complexity of RRI fluctuations. The effect is associated with the cardiac vagotonic drug action of propranolol. SAP fluctuations are almost unchanged. The increased complexity of RRI fluctuations may be a beneficial feature of beta-blockade, since many cardiovascular diseases decrease the complexity of RRI time series by dampening cardiovascular reflex actions.

Cardiovascular effects of ophthalmic 0.5% timolol aqueous solution and 0.1% timolol hydrogel

The objective of this randomized, double-masked, cross-over study was to compare the cardiovascular effects of two glaucoma formulations, ophthalmic 0.5% timolol aqueous solution and 0.1% timolol hydrogel. Twenty-four young healthy subjects received for 2 weeks either twice daily 0.5% timolol solution or once daily 0.1% timolol hydrogel. Heart rate (HR), blood pressure, atrio-ventricular conduction (PR interval), corrected QT time (QTc) and heart rate variability (HRV) were measured in supine position and during head-up tilted position. The mean peak concentrations of timolol in plasma were significantly higher after administration of 0.5% aqueous solution than after 0.1% hydrogel. A 0.5% timolol aqueous solution decreased HR on average by 3 bpm in supine position and by 7 bpm in head-up tilted position while no significant effects were observed with 0.1% timolol hydrogel. During tilt test HR was significantly lower after administration of timolol aqueous solution than after timolol hydrogel (mean +/- SD, 77 +/- 11 bpm versus 86 +/- 13 bpm, P < 0.05). Timolol aqueous solution slightly decreased QTc during tilt (5.9 +/- 5.6 ms, P < 0.01). During tilt tests, timolol aqueous solution slightly increased atrio-ventricular conduction (7.2 ms, P = 0.02). No significant differences were found in HRV. These results indicate that in healthy volunteers, ophthalmic 0.5% timolol aqueous solution produces more pronounced cardiac beta-blocking effects than 0.1% timolol hydrogel.

The acute effects of inhaled salbutamol on the beat-to-beat variability of heart rate and blood pressure assessed by spectral analysis

AIMS

We wanted to study the effects of a 600 micrograms inhaled salbutamol dose on the cardiovascular and respiratory autonomic nervous regulation in eight children suffering from bronchial asthma.

METHODS

In this randomized, double-blind, placebo-controlled, crossover study we continuously measured electrocardiogram, finger systolic arterial pressure (SAP) and flow-volume spirometry at baseline as well as 20 min and 2 h after the drug inhalation. The R-R interval (the time between successive heart beats) and SAP variabilities were assessed by using spectral analysis. Baroreflex sensitivity was assessed by using cross-spectral analysis.

RESULTS

Salbutamol significantly decreased the total and low frequency (LF) variability of R-R intervals as well as the high frequency (HF) variability of R-R intervals and of SAP. Salbutamol significantly increased the LF/HF ratio of R-R intervals and of SAP, minute ventilation, heart rate and forced pulmonary function in comparison with placebo. The weight of the subjects significantly correlated positively with baroreflex sensitivity and negatively with heart rate after the salbutamol inhalation.

CONCLUSIONS

We conclude that the acute salbutamol inhalation decreases cardiovagal nervous responsiveness, increases sympathetic dominance in the cardiovascular autonomic balance, and has a tendency to decrease baroreflex sensitivity in addition to improved pulmonary function.

Measurement of myocardial accumulation of 123I-metaiodobenzylguanidine for studying cardiac autonomic neuropathy in diabetes mellitus

The association of myocardial 123I-metaiodobenzylguanidine (MIBG) accumulation and autonomic neuropathy, as well as factors known to affect autonomic nervous function, were studied in a group of 12 diabetic patients representing different degrees of autonomic failure. The early myocardial uptake phase of 123I-MIBG was measured by calculating the peak net influx rate for the first 30 min after the 123I-MIBG injection and by single photon emission computed tomography (SPECT) imaging 1 h after the injection. The retainment of 123I-MIBG in the myocardium was measured using SPECT imaging 6 h after the injection, and myocardial uptake and the myocardium/liver uptake ratio were calculated. The 6-h myocardium/liver uptake ratio of 123I-MIBG was significantly (p < 0.05) lower in the diabetic patients with clinically evident autonomic neuropathy compared with those without autonomic neuropathy. Greater body mass index was associated with lower peak net influx rate and 1-h myocardial uptake of 123I-MIBG, and greater diastolic blood pressure was associated with lower 1-h myocardial uptake of 123I-MIBG, whether or not the patients had diabetic autonomic neuropathy. In conclusion, reduction in the 6-h myocardium/liver uptake ratio of 123I-MIBG is related to diabetic autonomic neuropathy. Because the early 123I-MIBG accumulation in myocardium is reduced in diabetic patients with greater body mass index and diastolic blood pressure, irrespective of autonomic neuropathy, our results encourage the use of the late myocardial accumulation of 123I-MIBG for studying sympathetic neuropathy in the diabetic heart.

Good exercise capacity at hospital discharge predicts recovery of baroreflex sensitivity after myocardial infarction

Myocardial infarction results in depressed baroreflex sensitivity, which has been shown to be associated with increased risk of ventricular arrhythmias and sudden death. We measured baroreflex sensitivity in 37 patients with acute myocardial infarction before hospital discharge and 3 months after the infarction to find out whether the baroreflex sensitivity recovers during that period. In addition, baroreflex sensitivity was assessed in 15 healthy controls. Baroreflex sensitivity was assessed from the regression line relating the change in R-R interval to the change in systolic blood pressure following an intravenous bolus injection of phenylephrine. There was a wide inter-individual variation in the change of baroreflex sensitivity (delta baroreflex sensitivity) in infarction patients, but the average baroreflex sensitivity showed no significant change during the 3-month follow-up (10.2 + 5.6 to 11.8 +/- 7.5 ms.mmHg-1, ns) and remained lower than the baroreflex sensitivity of the controls (16.4 +/- 9.7 ms.mmHg-1, P < 0.05). delta Baroreflex sensitivity correlated significantly with exercise capacity measured before hospital discharge. When the patients were divided into tertiles according to the delta baroreflex sensitivity (-3.3 +/- 1.5 ms.mmHg-1 in the lowest tertile, 1.0 +/- 1.0 ms.mmHg-1 in the middle tertile and 7.5 +/- 4.0 ms.mmHg-1 in the highest tertile) the exercise capacity was found to increase from the lowest to the highest tertile (exercise time 357 +/- 115 s, 418 +/- 126 s and 461 +/- 141 s, respectively; P < 0.05 lowest vs highest tertile). Patients with a low exercise tolerance (exercise time < 360 s) showed a significantly smaller delta baroreflex sensitivity than patients with a good exercise tolerance (exercise time > or = 480 s) (-0.5 +/- 4.4 vs 5.3 +/- 5.4 ms.mmHg-1, P < 0.05), respectively. delta Baroreflex sensitivity was not related to the location or type of infarction, thrombolytic therapy, presence of angina pectoris or left ventricular function at the time of discharge. In conclusion, exercise capacity assessed before hospital discharge seems to be a predictor of baroreflex sensitivity recovery in patients with a recent myocardial infarction.

Baroreflex sensitivity and neurohormonal activation in patients with acute myocardial infarction

OBJECTIVE

To examine the relationship between baroreflex sensitivity and neurohormonal activation in patients with an acute myocardial infarction.

METHODS

Baroreflex sensitivity, plasma noradrenaline, atrial natriuretic factor, endothelin-1, and plasma renin activity were measured in 37 male patients about 10 days after their first myocardial infarction, and in 15 healthy controls. Baroreflex sensitivity was assessed from the regression line relating the change in RR interval to the change in systolic blood pressure following an intravenous bolus injection of phenylephrine. The measurements were repeated after a follow up of three months.

RESULTS

There was a significant inverse correlation between baroreflex sensitivity and plasma noradrenaline measured before hospital discharge (r = -0.43, P < 0.01). Patients with increased plasma noradrenaline (> or = 2SD above the mean of the age matched control group) had significantly lower baroreflex sensitivity than patients with normal plasma noradrenaline (8.7 (SD 4.6) v 12.1 (6.1) ms/mm Hg, P < 0.05). The change in baroreflex sensitivity during the follow up showed a significant inverse correlation with the change of plasma noradrenaline (r = -0.450, P < 0.01). Furthermore, when patients with increased plasma noradrenaline before hospital discharge were analysed separately, baroreflex sensitivity at three months in patients in whom plasma noradrenaline had decreased to normal values was significantly higher than in patients in whom plasma noradrenaline had remained increased (14.6 (5.7) v 8.1 (8.1) ms/mm Hg, P < 0.05). On the other hand, baroreflex sensitivity was not related to the levels of plasma atrial natriuretic factor, plasma endothelin-1, or plasma renin activity. Neither was any relationship found between change in baroreflex sensitivity and change in plasma atrial natriuretic factor, endothelin-1, or plasma renin activity during the follow up.

CONCLUSIONS

The impairment baroreflex sensitivity after myocardial infarction was associated with increased concentration of plasma noradrenaline, that is, sympathetic activation, but not with plasma atrial natriuretic factor, endothelin-1, or plasma renin activity. Baroreflex sensitivity provides information about cardiac vagal control as well as about the balance of cardiac sympathetic-parasympathetic regulation.

Myocardial sympathetic nervous dysfunction detected with iodine-123-MIBG is associated with low heart rate variability after myocardial infarction

The association between myocardial sympathetic innervation and heart rate variability after myocardial infarction was studied in a group of 12 men (aged 30-65 yr) 3 mo after their first myocardial infarction.

METHODS

Viable myocardium was imaged using 123I-phenylpentadecanoic acid (pPPA). Functioning myocardial sympathetic nervous tissue was imaged using [123I]-metaiodobenzylguanidine (MIBG). Heart rate variability was measured as the ratio of maximum-to-minimum RR intervals in ECG during deep breathing.

RESULTS

The patients were divided into normal (n = 6) and low (n = 6) heart rate variability groups. Myocardial infarction size (pPPA defect) was comparable in the normal and low heart rate variability groups. Even the MIBG defect size was not significantly different in the normal and low groups, the portion of viable myocardium with impaired sympathetic innervation (MIBG defect minus pPPA defect) was significantly greater in the low heart rate variability group than in the normal group.

CONCLUSION

The extent of viable myocardium with disturbed sympathetic innervation was greater in patients with low heart rate variability as compared to those with normal heart rate variability 3 mo after myocardial infarction.

Baroreflex sensitivity in men with recent myocardial infarction; impact of age

We investigated the effect of age on baroreflex sensitivity (BRS) in 39 male patients, who had survived their first myocardial infarction (MI) and in 15 age-matched controls. BRS was inversely related to age in both MI patients (r = -0.632, P < 0.0001) and controls (r = -0.706, P < 0.0001). The relationship between BRS and age, however, was significantly different in MI patients as compared with healthy controls: BRS was markedly higher and the BRS-age regression slope was significantly steeper in controls than in MI patients. As a consequence, the decrease in BRS caused by MI (delta BRS = age-specific expected BRS--measured BRS) was related inversely to age (r = -0.66, P < 0.05) i.e. delta BRS was greatest among young MI patients. However, the relative BRS (BRS% = measured BRS divided by the age-specific expected BRS) did not correlate with age. The average BRS% of MI patients was 37% lower than that of controls. MI size and left ventricular (LV) systolic function did not correlate with BRS. BRS correlated with variables related to cardiac diastolic function (peak late LV filling rate r = -0.43, P < 0.05), exercise capacity (r = 0.31, P < 0.05) and the extent of ST-depression during exercise (r = -0.40, P < 0.05), but all these correlations lost their significance after the adjustment for age. In conclusion, age is a factor that should be taken into consideration when evaluating the mechanisms of BRS impairment associated with different diseases.(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian variation of cardiac autonomic regulation during 24-h bed rest

We examined the effect of circadian variation on cardiac autonomic regulation in 11 young and middle-aged, healthy men during 24-h bed rest. Cardiac parasympathetic regulation expressed significant circadian variation: sensitivity of baroreceptor reflex, standard deviation of R-R intervals and the power of high frequency component of R-R interval variability (HFP) increased during the evening (2000-2100 h), were highest during the night (0200-0300 h), and gradually decreased again towards afternoon (1400-1500 h). Cardiac sympathetic regulation, the power of medium frequency component of R-R interval variability (MFP), did not show any significant circadian variation. The autonomic response to orthostatic stress changed after the 24-h bed rest; the sympathetic dominance in response to assuming upright position was before bed rest principally attributable to increased sympathetic activity (MFP increase), whereas after bed rest this was due to withdrawal of parasympathetic activity (HFP decrease). We conclude that the effect of circadian variation must be taken into account, while assessing cardiac autonomic regulation in patients with acute cardiovascular disorders.

Noninvasive detection of cardiac sympathetic nervous dysfunction in diabetic patients using [123I]metaiodobenzylguanidine

The association between clinical autonomic dysfunction and myocardial MIBG accumulation was investigated. The study groups comprised 6 male diabetic patients with autonomic neuropathy (ANP+ group), 6 male diabetic patients without autonomic neuropathy (ANP-group), and 6 male nondiabetic control subjects. The mean age was comparable in all groups, and the subjects had no evidence of coronary heart disease. Reduced heart-rate variation in a deep-breathing test was used as a criterion for autonomic neuropathy. Immediately after injection, the peak net influx rate of MIBG to myocardium was significantly (P less than 0.05) reduced in both diabetic groups. At 6 hr after MIBG injection, the MIBG uptake of the myocardium was significantly (P less than 0.05) smaller in the ANP+ group than in the control group. In the ANP- group, the MIBG uptake of the myocardium was between that of the ANP+ group and that of the control group. Our data show that reduced myocardial MIBG accumulation is associated with autonomic dysfunction in diabetic patients, but it can occur to a lesser extent also in diabetic patients without apparent autonomic neuropathy. The measurement of the myocardial MIBG accumulation is a promising new method to detect cardiac sympathetic nervous dysfunction in diabetic patients.

Microcomputer-based monitoring of cardiovascular functions in simulated microgravity

A microcomputer-based system for non-invasive monitoring of cardiovascular system in simulated microgravity is described. The system evaluates automatically, accurately and interactively heart beat intervals, beat-to-beat non-invasive finger arterial blood pressure (systolic, diastolic, mean and pulse pressure) using a Finapres device and beat-to-beat changes of thoracic blood volume using impedance changes. In addition, beat-to-beat evaluation of cardiac mechanical function including left ventricular ejection time, diastolic time, systolic time intervals, left ventricular ejection fraction estimate and several other contractility parameters, left ventricular volume, stroke volume and cardiac output estimates are performed with high degree of automaticity.

Compartment syndrome as a late complication of eosinophilic fasciitis

Eosinophilic fasciitis (EF) was diagnosed in a 23-year-old man presenting characteristic symptoms, skin changes, blood eosinophilia and typical histology showing thickened deep dermal fascia with inflammatory cells. After one year of corticosteroid treatment he experienced increasing pain in both legs and fluctuating serum creatinine kinase levels. Direct measurement showed elevated resting intracompartment pressure and both static strain and dynamic exercise provoked the typical pain. At operation all 4 compartments of both legs were decompressed and he recovered uneventfully. The compartment syndrome may be a hitherto unknown, but expected complication of severe EF.

Impaired left ventricular systolic function during exercise in middle-aged insulin-dependent and noninsulin-dependent diabetic subjects without clinically evident cardiovascular disease

Equilibrium radionuclide angiocardiography was performed on 19 men and 17 women with insulin-dependent diabetes mellitus (IDDM) and on 24 men and 15 women with noninsulin-dependent diabetes mellitus (NIDDM) and on 24 male and 24 female control subjects aged 46 to 67 years. All were without clinically evident cardiovascular disease. No significant differences were found in left ventricular (LV) ejection fraction at rest between men with IDDM (56 +/- 1%; mean +/- standard error of the mean) or NIDDM (58 +/- 1%) and control men (58 +/- 1%), whereas LV ejection fraction was higher in women with IDDM (63 +/- 1%; p less than 0.01) and NIDDM (64 +/- 2%; p less than 0.01) than in control women (58 +/- 1%). An abnormal LV ejection fraction response to dynamic exercise (an increase of less than 5% units or a decrease) was observed in 1 control man (4%), in 8 men with IDDM (42%, p less than 0.01) and in 10 men with NIDDM (42%, p less than 0.01). The respective figures were 4 (17%) for control women, 7 (44%, difference not significant) for women with IDDM and 10 (71%, p less than 0.01) for women with NIDDM. Abnormal LV ejection fraction response to exercise in diabetic patients was not related to the metabolic control of diabetes, presence of microangiopathy or abnormalities in the autonomic nervous function. Myocardial perfusion scintigraphy performed in 18 diabetic patients in whom LV ejection fraction decreased during exercise showed a reversible perfusion defect in only 5 (28%).(ABSTRACT TRUNCATED AT 250 WORDS)

Combined effect of low doses of propranolol and ethanol on cardiac function: a comparative study by radionuclide ventriculography in conscious dogs

Trained, chronically instrumented, conscious dogs were used to evaluate the effect of propranolol (PRO), ethanol (ETH) or their combination (P + E) on the left ventricular (LV) function by first-pass radionuclide ventriculography (RNV). Six dogs were trained prior to a sterile left thoracotomy, where a left atrial catheter was implanted. After recovery of four days RNV was carried out by injecting a bolus of technetium-99m diethylenetriamine pentaacetic acid via the catheter to the left atrium. The data was collected for 12 sec. to a computer by frame rate of 20 frames/sec. from left lateral view of the dog. The experiments were performed both in four-leg standing and in 60-degree head-up tilted positions. After control measurements the data were obtained with 0.5 mg/kg of PRO, 0.45 g/kg of ETH and their combination. The P + E combination increased significantly LV end-diastolic and end-systolic volumes, whereas LV peak ejection rate and ejection fraction were decreased. Upright position diminished the LV volume and increased heart rate, while ejection fraction and cardiac output remained unchanged. The first-pass RNV method proved to be promising for measuring the cardiac pharmacological effects in conscious dogs. The combination of propranolol and ethanol in low doses induced an unexpectedly strong depression of LV function, which is supposed to be followed of latent cardiac depressing effect of ETH revealed by blockade of compensatory adrenergic mechanisms with PRO.

First-pass radionuclide ventriculography in conscious dogs

Trained, chronically instrumented, conscious dogs were used to study the function of the left ventricle by first-pass radionuclide ventriculography (RNV). Six dogs were trained prior to a sterile left thoracotomy, where a left atrial catheter was implanted. After recovery of four days RNV was carried out by injecting a bolus of technetium-99m-DTPA via the catheter to the left atrium. The data was collected for 12 s to a computer by frame rate of 20 frames/s from left lateral view of the dog. The experiments were performed both in four-leg standing and in 60 degrees head-up tilted positions. The measurements were done with two injection volumes (0.25 and 1.0 ml/kg) to study the effect of volume on the results. The body position had effect on left ventricular end-diastolic and stroke volumes, whereas ejection fraction remained unchanged. In comparison of the two injection volumes a minor difference was found in left atrial emptying, while the differences in left ventricular function were non-significant. In spite of training and careful standardization of experimental procedures, relatively high individual variation between animals was found in most parameters studied. The first-pass RNV method proved to be promising for measuring the left ventricular function in conscious dogs. Although the left atrium has reflectory tachycardic potential to distension, the volumes used for RNV did not affect the results. The left ventricular adaptation to head-up tilting in conscious dogs seems to consist mainly of decrease in left ventricular volume without significant effect on ejection fraction.

Acute effects of dihydralazine mesylate, furosemide, and metoprolol on maternal hemodynamics in pregnancy-induced hypertension

The intervillous blood flow and other maternal hemodynamic parameters were assessed in 40 mothers with pregnancy-induced hypertension in late pregnancy before and after hypotensive treatment. Furosemide caused a significant decrease in the intervillous blood flow, whereas the effects of dihydralazine and metoprolol were both negative and positive, that is, more individual and diverse. These changes in the intervillous blood flow did not have any correlation with the changes in other maternal hemodynamic parameters. The importance of placental hemodynamic studies in the evaluation of hypotensive drugs is stressed.