Within-session Reproducibility Research Articles

3D Creatine Kinase Imaging (CKI) for In Vivo Whole-Brain Mapping of Creatine Kinase Reaction Rates with 31P-Magnetization Transfer MR Fingerprinting.

The creatine kinase (CK) is a key enzyme involved in brain bioenergetics, but imaging its activity noninvasively in the human brain remains a significant challenge. This study aims to advance the magnetization transfer (MT)-31P magnetic resonance fingerprinting (MRF) framework for 3D Creatine Kinase Imaging (CKI), delivering the first whole-brain CK reaction rate maps. The method was implemented and validated on a clinical 7 Tesla MRI scanner with a 49:30-minute acquisition time and the within-session reproducibility was assessed. The CKI method successfully enables the whole-brain mapping of CK reaction rates, showing robust reproducibility with coefficients of variation (CV) below 11% for 25-minute scan sessions. Furthurmore, CKI acquisition provided simultaneous mapping of adenosine triphosphate (ATP) and phosphocreatine (PCr) concentrationratios, PCr longitudinal relaxation time (T 1 PCr ), and phosphorus-based B0 maps at a 7.2 × 7.2 × 20 mm 3 resolution. CKI provides, for the first time,3D whole-brain mapping of k CK rates in high resolution, using a user-friendly, push-button approach. A functional CKI (fCKI) study demonstrated the first CK activation cluster map in response to visual stimulation, revealing a mean 17% increase in CK rates in the visual cortex. The novel imaging modalities, CKI and fCKI, have the potential to offer new insights into brain bioenergetics both at rest and during activity.

Reproducibility assessment of a biomechanical model-based elasticity imaging method for identifying changes in left ventricular mechanical stiffness.

Cardiotoxicity of antineoplastic therapies is increasingly a risk to cancer patients treated with curative intent with years of life to protect. Studies highlight the importance of identifying early cardiac decline in cancer patients undergoing cardiotoxic therapies. Accurate tools to study this are a critical clinical need. Current and emerging methods for assessing cardiotoxicity are too coarse for identifying preclinical cardiac degradation or too cumbersome for clinical implementation. In the previous work, we developed a noninvasive biomechanical model-based elasticity imaging methodology (BEIM) to assess mechanical stiffness changes of the left ventricle (LV) based on routine cine cardiac magnetic resonance (CMR) images. We examine this methodology to assess methodological reproducibility. We assessed a cohort of 10 participants that underwent test/retest short-axis CMR imaging at baseline and follow-up sessions as part of a previous publicly available study. We compare test images to retest images acquired within the same session to assess within-session reproducibility. We also compare test and retest images acquired at the baseline imaging session to test and retest images acquired at the follow-up imaging session to assess between-session reproducibility. We establish the within-session and between-session reproducibility of our method, with global elasticity demonstrating repeatability within a range previously demonstrated in cardiac strain imaging studies. We demonstrate increased repeatability of global elasticity compared to segmental elasticity for both within-session and between-session. Within-subject coefficients of variation for within-session test/retest images globally for all modulus directions and a mechanical fractional mechanical stiffness anisotropy metric ranged from 11% to 28%. Results suggest that our methodology can reproducibly generate estimates of relative mechanical elasticity of the LV and provides a threshold for distinguishing true changes in myocardial mechanical stiffness from experimental variation. BEIM has applications in identifying preclinical cardiotoxicity in breast cancer patients undergoing antineoplastic therapies.

Within-session reproducibility of forced oscillometry.

The forced oscillation technique (FOT) provides detailed information about the mechanics of the respiratory system, while requiring minimal co-operation by the patient. FOT may be abnormal in subjects with normal spirometry and appears to be more closely related to airway symptoms. It is, therefore, attractive in epidemiological studies, where a large number of different examinations are made in each subjects in a short period of time. Current technical standards recommend the mean of three consecutive measurements to be used, but there is limited information regarding within-session variability of FOT measurements. The purpose of this study was to examine the within-session variability in FOT measurements in a large, population-based sample. We performed three consecutive FOT measurements in 700 subjects using the impulse oscillometry system. The first measurement was compared to the mean of three measurements for resistance at 5 and 20Hz (R5 and R20, respectively), R5-R20, reactance at 5Hz (X5) and resonant frequency (fres ). The differences between the first and the mean of three measurements (median, interquartile range) were minimal, for example 0.002, -0.008 to 0.014kPa L-1 s for R5 and -0.001, -0.008 to 0.005kPa L-1 s for X5. Findings were numerically similar for men and women as well as for subjects with and without airflow obstruction at spirometry. We conclude that, whereas in clinical situations, three FOT measurements are to be preferred, a single measurement may suffice in epidemiological studies.

Reproducibility of lower limb motion and forces during stationary submaximal pedalling using wearable motion tracking sensors

ABSTRACT In order to address gaps in the literature, this study assessed the reproducibility (i.e., difference between and within sessions) of joint and muscle forces using wearable sensors during stationary cycling. Seventeen male cyclists performed two sessions on a cycle ergometer cycling at a combination of three power outputs (1.5, 2.5 and 3.5 W/kg) and three pedalling cadences (60, 80 and 100 rpm) in two sessions (2–7 days apart). The first trial from each session was repeated at the end of the session for assessment of within-session reproducibility. Three-dimensional (3D) full-body motion and 3D bilateral pedal forces were collected using an inertial motion tracking system and a pair of instrumented pedals, respectively. Joint angles, muscle forces and knee joint forces were computed using OpenSim. Poor to excellent agreement (ICCs = 0.31–0.99) was observed and differences were trivial to small and non-significant between trials within-session. Poor to excellent agreement (ICCs = 0.05–0.97) was observed and differences were trivial to large between sessions. Variability can be attributed to changes in muscle recruitment strategies (within and between-sessions) and to repositioning of sensors (between-sessions).

Acute Intermittent Hypoxia and Cortical Evoked Potentials in Human Diaphragm

Episodic carotid body activation via acute intermittent hypoxia (AIH) elicits respiratory motor plasticity (known as long‐term facilitation [LTF]) in humans and other mammals. In rodents, AIH‐induced LTF requires serotonergic neuron activation in the medullary raphe nuclei and episodic serotonin release within respiratory motor nuclei, thereby strengthening descending synaptic inputs to spinal respiratory motor neurons. Humans exhibit ventilatory LTF under certain circumstances, although the details of its underlying mechanism are less clear. Recent evidence demonstrates that AIH enhances corticospinal motor evoked potentials (MEP) in a non‐respiratory motor pool innervating the first dorsal interosseous muscle of the hand. It is not known if AIH has similar effects on the phrenic/diaphragm system in humans. Thus, we tested the hypothesis that AIH augments diaphragm MEP amplitude. Twelve healthy young adults were recruited (age = 30 ± 7 years; 5 female). On Day 1, diaphragm MEPs and compound muscle action potentials (CMAPs) were assessed using transcranial (TMS) and cervical (CMS) magnetic stimulation, respectively. The diaphragm electromyogram was recorded using surface electrodes on the chest wall. Reliability of TMS‐ and CMS‐evoked potentials were determined prior to testing. Following baseline measures, subjects were exposed to AIH (15, 1‐minute episodes of 9% O2, with 1‐minute normoxic intervals) via a facemask attached to a hypoxic generator. Cardiovascular responses (heart rate, blood pressure and oxygen saturation) were monitored throughout. Stimulus‐response curves were determined for each subject by delivering stimuli prior to and 30 minutes post AIH. On Day 2 (at least 7 days later), 6 subjects returned for a normoxic (sham) trial. Subjects were blinded to the gas composition delivered on each visit. No significant AIH effects were observed in MEP (change = −1 ± 7%, p= 0.96) or CMAP amplitude (+1 ± 5%, p= 0.97) across the stimulus‐response curve. At an intensity equivalent to 50% of baseline peak amplitude (V50), the mean changes in MEP and CMAP amplitude were +4 ± 14% (p= 0.81) and −5 ± 6% (p= 0.75), respectively. Further, no effect of normoxic sham exposures was found during the control visit (MEP = −8 ± 9%, p= 0.97; CMAP = +7 ± 31%, p= 0.79). Between‐block coefficients of variation for TMS‐ and CMS‐evoked potentials were 22.9% and 6.9%, respectively. Within‐session reproducibility of evoked responses to TMS and CMS were good to excellent (ICC > 0.8). In conclusion, AIH alone does not influence cortical evoked potentials in the diaphragm as it does in a non‐respiratory motor system. We speculate that repetitive daily AIH and/or concomitant hypercapnia during AIH may reveal plasticity in diaphragm cortical evoked potentials in humans.Support or Funding InformationThis work was supported by the UF McKnight Brain Institute, DoD (SCIRP), NIH R01 HL147554 & OT2OD023854, Brooks Rehabilitation, and the Brooks PHHP Research Collaboration.

Test–retest reliability of spatial patterns from resting-state functional MRI using the restricted Boltzmann machine and hierarchically organized spatial patterns from the deep belief network

BackgroundRestricted Boltzmann machines (RBMs), including greedy layer-wise trained RBMs as part of a deep belief network (DBN), have the ability to identify spatial patterns (SPs; functional networks) in resting-state fMRI (rfMRI) data. However, there has been little research on (1) the reproducibility and test-retest reliability of SPs derived from RBMs and on (2) hierarchical SPs derived from DBNs. MethodsWe applied a weight sparsity-controlled RBM and DBN to whole-brain rfMRI data from the Human Connectome Project. We evaluated the within-session reproducibility and between-session test-retest reliability of the SPs derived from the RBM approach and compared them both with those identified using independent component analysis (ICA) and with three voxel-wise statistical measures—the Hurst exponent, entropy, and kurtosis—of the rfMRI data. We also assessed the potential hierarchy of the SPs from the DBN. ResultsAn increase in the sparsity level of the RBM weights enhanced the reproducibility of the SPs. The SPs deriving from a stringent weight sparsity level were predominantly found in the cortical gray matter and substantially overlapped with the SPs obtained from the Hurst exponent. A hierarchical representation was shown by constructed using the default-mode network obtained from the DBN. Comparison with existing methodsThe test-retest reliability of the SPs from the RBM was superior to that of the SPs from the voxel-wise statistics. ConclusionsThe SPs from the RBM were reproducible within sessions and reliable across sessions. The hierarchically organized SPs from the DBN could possibly be applied to research based on rfMRI data.

A graphic user interface for the evaluation of knee osteoarthritis (GEKO): an open-source tool for histological grading

In osteoarthritis (OA) models, histology is commonly used to evaluate the severity of joint damage. Unfortunately, semi-quantitative histological grading systems include some level of subjectivity, and quantitative grading systems can be tedious to implement. The objective of this work is to introduce an open source, graphic user interface (GUI) for quantitative grading of knee OA. Inspired by the 2010 OARSI histopathology recommendations for the rat, our laboratory has developed a GUI for the evaluation of knee OA, nicknamed GEKO. In this work, descriptions of the quantitative measures acquired by GEKO are presented and measured in 42 histological images from a rat knee OA model. Using these images, across-session and within-session reproducibility for individual graders is evaluated, and inter-grader reliability across different levels of OA severity is also assessed. GEKO allowed histological images to be quantitatively scored in less than 1min per image. In addition, intra-class coefficients (ICCs) were largely above 0.8 for across-session reproducibility, within-session reproducibility, and inter-grader reliability. These data indicate GEKO aided in the reproducibility and repeatability of quantitative OA grading across graders and grading sessions. Our data demonstrate GEKO is a reliable and efficient method to calculate quantitative histological measures of knee OA in a rat model. GEKO reduced quantitative grading times relative to manual grading systems and allowed grader reproducibility and repeatability to be easily assessed within a grading session and across time. Moreover, GEKO is being provided as a free, open-source tool for the OA research community.

Fully automated quality assurance and localization of volumetric MEG for single-subject mapping

BackgroundRobust and reproducible source mapping with magnetoencephalography is particularly challenging at the individual level. We evaluated a receiver-operating characteristic reliability (ROC-r) method for automated production of volumetric MEG maps in single-subjects. ROC-r provides quality assurance comparable to that offered by goodness-of-fit (GoF) and confidence volume (CV) for equivalent current dipole (ECD) modeling. New methodROC-r utilizes within-session reproducibility for quality assurance, latency identification, and thresholding of volumetric source maps. We tested ROC-r on simulated and real MEG with a strongly focal source, using somatosensory evoked fields (SEFs) elicited by bilateral median nerve stimulation (MNS). For quality assurance, the ROC-r reliable fraction (FR) was compared to the ECD GoF and CV. Peak beamformer locations and latencies identified by ROC-r were compared to the ECD for co-localization accuracy. ResultsThe predominant component of the SEF response occurred around 35ms, contralateral to the MNS. Comparison with existing methodsFR and 1/CV were more strongly correlated (mean Pearson’s correlation: 0.76; 95% CI 0.60–0.87) than FR and GoF (0.65; 95% CI 0.32–0.85). There was no difference in the latency of the peak GoF (35.0+/−0.6ms), CV (34.8+/−0.7ms) and FR (35.5+/−0.8ms). The ECD fits and ROC-r peaks co-localized to within a mean (median) distance of 8.3+/−5.9mm (6.2mm). ConclusionROC-r volumetric mapping co-localized closely with the standard ECD approach. This analysis can be added to any whole-brain MEG source imaging protocol, and is especially useful for single-subject mapping. Additionally, the development of FR as an analogue to GoF or CV for volumetric mapping is a critical improvement for clinical applications.

Scan-rescan reproducibility of parallel transmission based amide proton transfer imaging of brain tumors.

To evaluate the reproducibility of amide proton transfer (APT) imaging of brain tumors using a parallel transmission-based technique. Thirteen patients with brain tumors (four low-grade gliomas, three glioblastoma multiforme, five meningiomas, and one malignant lymphoma) were included in the study. APT imaging was conducted at 3T using a 2-channel parallel transmission scheme with a saturation time of 2 seconds and B1 amplitude of 2 μT. A 2D fast spin-echo sequence with driven-equilibrium refocusing was used for imaging. Z-spectra were obtained at 25 frequency offsets from -6 to +6 ppm (step 0.5 ppm). A point-by-point B0 correction was performed with a B0 map. A scan-rescan reproducibility test was performed in two sessions on separate days for each patient. The interval between the two sessions was 4.8 ± 3.5 days. Regions-of-interest (ROIs) were placed to include the whole tumor for each case. A mean and 90-percentile value of APT signal for the whole tumor histogram was calculated for each session. The between-session and within-session reproducibility was evaluated using linear regression analysis, intraclass correlation coefficient (ICC), and a Bland-Altman plot. The mean and 90-percentile values of the APT signal for whole tumor ROI showed excellent agreements between the two sessions, with R(2) of 0.91 and 0.96 in the linear regression analysis and ICC of 0.95 and 0.97, respectively. Parallel transmission-based APT imaging of brain tumors showed good reproducibility.

Unedited in vivo detection and quantification of γ-aminobutyric acid in the occipital cortex using short-TE MRS at 3 T.

Short-TE MRS has been proposed recently as a method for the in vivo detection and quantification of γ-aminobutyric acid (GABA) in the human brain at 3 T. In this study, we investigated the accuracy and reproducibility of short-TE MRS measurements of GABA at 3 T using both simulations and experiments. LCModel analysis was performed on a large number of simulated spectra with known metabolite input concentrations. Simulated spectra were generated using a range of spectral linewidths and signal-to-noise ratios to investigate the effect of varying experimental conditions, and analyses were performed using two different baseline models to investigate the effect of an inaccurate baseline model on GABA quantification. The results of these analyses indicated that, under experimental conditions corresponding to those typically observed in the occipital cortex, GABA concentration estimates are reproducible (mean reproducibility error, <20%), even when an incorrect baseline model is used. However, simulations indicate that the accuracy of GABA concentration estimates depends strongly on the experimental conditions (linewidth and signal-to-noise ratio). In addition to simulations, in vivo GABA measurements were performed using both spectral editing and short-TE MRS in the occipital cortex of 14 healthy volunteers. Short-TE MRS measurements of GABA exhibited a significant positive correlation with edited GABA measurements (R = 0.58, p < 0.05), suggesting that short-TE measurements of GABA correspond well with measurements made using spectral editing techniques. Finally, within-session reproducibility was assessed in the same 14 subjects using four consecutive short-TE GABA measurements in the occipital cortex. Across all subjects, the average coefficient of variation of these four GABA measurements was 8.7 ± 4.9%. This study demonstrates that, under some experimental conditions, short-TE MRS can be employed for the reproducible detection of GABA at 3 T, but that the technique should be used with caution, as the results are dependent on the experimental conditions.

In vivo detection of GABA and glutamate with MEGA‐PRESS: Reproducibility and gender effects

To evaluate the reproducibility of γ-amino-butyric acid (GABA) and glutamate concentrations derived using three different spectral fitting methods, and to investigate gender-related differences in neurotransmitter levels. Single voxel MEGA-edited PRESS MR spectra were acquired from a 30-mL voxel in the dorso-lateral prefrontal cortex in 14 adult volunteers (7 female) at 3 Tesla (3T). For each participant, four consecutive resting spectra were acquired within the same scanning session. Metabolite concentrations were derived using LCModel, jMRUI, and locally written peak fitting software. The within-session reproducibility for each analysis method was calculated as the average coefficient of variation (CV) of the GABA and Glx (glutamate+glutamine) concentrations. Gender differences in GABA and Glx were evaluated using a two-tailed unpaired t-test. LCModel provided the best reproducibility for both GABA (CV 7%) and Glx (CV 6%). GABA, Glx, and glutamate concentrations were significantly higher in the male participants, (P = 0.02, P = 0.001, and P < 0.001, respectively). GABA and glutamate can be quantified in vivo with high reproducibility (CV 6-7%) using frequency-domain spectral fitting methods like LCModel. However, the GABA and glutamate concentrations vary significantly between men and women, emphasizing the importance of gender-matching for studies investigating differences in neurotransmitter concentrations between mixed-cohort groups.

Test–retest reliability of arterial spin labeling with common labeling strategies

To compare the test-retest reproducibility of three variants of arterial spin labeling (ASL): pseudo-continuous (pCASL), pulsed (PASL) and continuous (CASL). Twelve healthy subjects were scanned on a 3.0T scanner with PASL, CASL, and pCASL. Scans were repeated within-session, after 1 hour, and after 1 week to assess reproducibility at different scan intervals. Comparison of within-subject coefficients of variation (wsCV) demonstrated high within-session reproducibility (ie, low wsCV) for CASL-based methods (gray matter [GM] wsCV for pCASL: 3.5% ± 0.02%, CASL: 4.1% ± 0.07%) compared to PASL (wsCV: 7.5% ± 0.06%), due to the higher signal-to-noise ratio (SNR) associated with continuous labeling, evident in the 20% gain in temporal SNR and 58% gain in raw SNR for pCASL relative to PASL. At the 1-week scan interval, comparable reproducibility between PASL (GM wsCV 9.2% ± 0.12%) and pCASL (GM wsCV 8.5% ± 0.14%) was observed, indicating the dominance of physiological fluctuations. Although all three approaches are capable of measuring cerebral blood flow within a few minutes of scanning, the high precision and SNR of pCASL, with its insensitivity to vessel geometry, make it an appealing method for future ASL application studies.

Variations in Exhaled Nitric Oxide in Children with Asthma During a 1-Week Stay in a Mountain Village Sanatorium

Knowing about spontaneous variations in the fractional concentration of exhaled nitric oxide (FENO) could improve monitoring of airway inflammation in asthmatic children. We aimed to assess FENO variations (expiratory flow 50 mL/sec) in subjects maintained in similar environmental conditions. We tested spirometry and FENO in symptom-free asthmatic children (9 corticosteroid-naive, 8 corticosteroid-treated) during a 1-week stay in a countryside sanatorium and in their healthy relatives (n = 12) staying in the immediate neighborhood on summer holiday (total 29 children, M/F:14/15, 5.8-16.8 yrs). Testing sessions were repeated every 12 hours (8:00 am, 8:00 pm) for 2 days and again on day 7. Measurements were defined as reproducible when they agreed with an intraclass correlation coefficient (ICC) above 0.60; deviation from mean differences was assessed by the coefficient of repeatability (CR = 2 SD). Lung function remained constant throughout the week in all groups. Baseline FENO levels in corticosteroid-naive asthmatic children tended to decrease at the end of the week (from 13.9 ppb, 95% CI 12.2-19.1 to 9.2 ppb, 95% CI 5.8–15.9, p = 0.057). No differences were found between nocturnal and diurnal FENO. Within-session reproducibility for two FENO measurements was high (ICC 0.99 in all groups and CR, 0.9 to 1.3 ppb). Between-session FENO reproducibility at 12 hours and 24 hours was still high for each group but decreased markedly after 6 days in corticosteroid-naive asthmatic children (ICC 0.79 and CR 9.6 ppb at 24 hours vs. ICC 0.13 and CR 20.8 ppb after 6 days), whereas it decreased slightly in corticosteroid-treated asthmatics (from ICC 0.89 and CR 3.1 ppb to ICC 0.88 and CR 3.0 ppb) and healthy children (from ICC 0.79 and CR 4.8 ppb to ICC 0.65 and CR 5.7 ppb). In conclusion, in healthy subjects and in asthmatic children receiving therapy with inhaled corticosteroids (but not in corticosteroid-naïve subjects), FENO measurements are reproducible across a week.

Within-session reproducibility of motion-onset VEPs: Effect of adaptation/habituation or fatigue on N2 peak amplitude and latency

We explored the effect of repeated visual stimulation on motion-onset visual evoked potentials (M-VEPs) during 25 min recording sessions in 10 subjects. The aim of the experiment was to determine influence of global motion adaptation (without motion-aftereffect) on intra-individual variability of M-VEPs and to suggest an optimal recording design for clinical examination. In addition to well described middle-time sensory adaptation, we also observed a long-time effect on motion specific N2 peak (155 ms). The N2 peak exhibited a strong relationship between its latency and inter-peak amplitude to the duration of recording in occipito-parietal derivations. In addition to the middle-term adaptation, N2 peak latency was prolonged by 10 ms and amplitude was attenuated by 30% with respect to the start of the experiment. An exponential model was employed to describe the dependency. The model can be used to reduce intra-individual variability during examination. Observed resemblance between the measured electrophysiological values and already published metabolic changes (glucose and oxygen utilization) during brain processing of visual information is discussed.

Pulmonary Function Electronic Monitoring Devices: A Randomized Agreement Study

To compare in a clinical setting the within-session reproducibility of two pulmonary function electronic monitoring devices (PiKo-1; Ferraris Respiratory Europe; Hereford, UK; and Spirotel; MIR; Rome, Italy) with one mechanical device (Mini-Wright Peak-Flow Meter; Clement-Clarke International; Harlow, Essex, UK), and to evaluate the accuracy of these devices using as reference an office pneumotachograph.After detailed instructions, adults without airways diseases and patients with stable asthma attending an outpatient clinic performed four sets of expiratory maneuvers, one set for each device, in a strictly random order. Each set comprised three maneuvers with 2 to 3 min of rest between them.Reproducibility of FEV1 and peak expiratory flow (PEF) was assessed by a coefficient of variation (CV) and intraclass correlation coefficient (ICC), and accuracy was assessed by ICC and limits of agreement.Of the 38 participants evaluated, 71% were women and 61% had asthma. Ages ranged from 18 to 58 years, and FEV1 ranged from 1.2 to 4.8 L. In all monitoring devices, CV was < 6% and ICC was > 0.94 for the reproducibility of both FEV1 and PEF measurements. The accuracy of the PiKo-1 device was better for FEV1 (ICC = 0.98) than for PEF (ICC = 0.90). The Spirotel device had similar results for FEV1 and PEF (ICC = 0.95). The Mini-Wright device had the lowest accuracy (ICC = 0.87), particularly for PEF values < 500 L/min.These low-cost and easy-to-use electronic monitoring devices showed a very good reproducibility and were in agreement with the pneumotachograph. Therefore, the PiKo-1 and Spirotel devices seem adequate for both screening and monitoring. However, prospective studies are still needed to assess their long-term reproducibility and usability and, particularly, the effects on the improvement of respiratory care.

Sources of variability in oxygen-15 PET studies in acute brain injury – impact on sample size estimation

The potential of Oxygen-15 positron emission tomography (PET) to investigate acute brain injury and the effect of therapeutic interventions is limited by inter- and intra-subject variability. We have tried to quantify these limitations when steady state PET is used to measure cerebral blood (CBF), cerebral blood volume (CBV), oxygen metabolism (CMRO2) and oxygen extraction fraction (OEF). We obtained PET images from 10 healthy volunteers and 24 patients within 10 days of head injury with a median (range) Glasgow Coma Score of 7 (3 – 13). Using a region of interest map comprising 15 regions covering the whole brain we calculated inter-subject variability in both groups, while the intra-subject variability was calculated from two consecutive PET studies in a cohort of six patients (test-retest reproducibility). The acquisition of PET data in two frames provided the opportunity of using individual frames to calculate two independent sets of metabolic images, which could be used to assess reproducibility within the context of a single pre-intervention baseline PET study (within-session reproducibility). In this way we obtained repeated measurements of CBF, CMRO2 and OEF, but not CBV, within the same study session in controls and patients under unchanged physiological conditions. We compared assessments of reproducibility obtained using these two approaches: the test-retest reproducibility (two independent studies) and the within-session reproducibility (two independent frames within a single study). Inter-subject coefficients of variation (CoV) for CBF, CBV, CMRO2 and OEF in patients (32.9 +/- 2.2, 15.2 +/- 2.1, 23.2 +/- 2.0 and 22.5 +/- 3.4 %) were generally larger than in controls (13.5 +/- 1.4, 22.5 +/- 2.8, 12.8 +/- 1.1 and 7.3 +/- 1.2 %). The CoV for the test-retest reproducibility measurements in patients were 2.1 +/- 1.5, 3.8 +/- 3.0, 3.7 +/- 3.0 and 4.6 +/- 3.5 %, respectively. The within-session reproducibility CoV for CBF, CMRO2 and OEF in patients (4.2 +/- 4.6, 2.2 +/- 2.0 and 4.8 +/- 4.7 %) were smaller than in controls (8.4 +/- 7.6, 5.3 +/- 3.9, 5.7 +/- 4.4 %). Although large inter-subject variability creates difficulties with studies of small patient groups, estimated sample sizes are moderated by the fact that the changes in cerebrovascular physiology in disease are often dramatic. These figures are irrelevant to the design of interventional studies, where the subject is his or her own control, and the relevant parameter is intra-subject variability or reproducibility. The CoV figures for reproducibility are substantially smaller and provide important reference data. In addition, the within-session and test-retest reproducibility measurements are comparable. This implies that within-session reproducibility measurements can be used to assess the significance of any change in physiology following a therapeutic intervention. These data provide guidance for designing interventional studies, and suggest it should be possible to detect differences of approximately 10 – 15% in controls, and 5 – 10% in head injured patients where systemic physiology is tightly controlled. While each centre should develop its own bank of such data, the figures provided will allow initial generic approximations of sample size for such studies.

Doppler Investigation of Within-Session Reproducibility in a Visual Stimulation Task to Assess the Volunteer-Dependent Variation

Objective: In functional magnetic resonance imaging (MRI) studies in humans the tightness of activity-flow coupling was questioned due to a notable within-session variability of the signals obtained. To differentiate between moments of volunteer-dependent or technique-inherent variation in hemodynamic MRI measurements a method with a low technique-inherent variation is needed. Therefore, and because temporal features might also be of some relevance, we used the transcranial Doppler method. Methods: In 22 healthy volunteers the flow-velocity response to a visual stimulation task was evaluated. Conditions of 20 s of eye closure were altered with 40 s of silent reading, repeated 10 times. Averaged individual flow-velocity responses were evaluated from conditions of 40 s of stimulation and a 5-second time interval prior to the beginning of stimulation. The averaged data were subtracted from each single recording to calculate the mean squared differences (MSD). Statistical evaluation was performed according to a two-way ANOVA for repeated measures. To obtain additional qualitative data of the flow response, the individual flow curves were evaluated according to a control system approach specifying a second-order linear model. Results: The coefficient of variation (COV) of the within-session MSD was 7% for the stimulation phase and 2.9% for the resting phase, whereas the respective COVs were 15 and 8.1% for the interindividual MSDs. The interindividual COVs of control system parameters ranged from 3.6 to 7.6%. The ANOVA resulted in a significant (p < 0.003) difference for the MSD values between stimulation conditions, whereas the test repetition (p = 0.55) and the test for an interaction of repetition and stimulation condition (p = 0.54) revealed no significance. Discussion: Confirming the notion of a tight coupling between cortical activity and cerebral blood flow and being indicative of a low technique-inherent variation, we found a high within-session reproducibility in a functional Doppler test.

Improving the quality of spirometry in an epidemiological study: The Renfrew–Paisley (Midspan) family study

Population studies in Britain and elsewhere report deficiencies in quality of pulmonary function measurements. Methods were tested to improve the standardisation of spirometry in an epidemiological study. The spirometer provided visual feedback about acceptability and reproducibility to American Thoracic Society (ATS) standards. After 14 weeks technicians (research nurses) were given feedback and further training. Measurements were repeated in a 5% sample. Participant characteristics and technical factors (technician and technician feedback) predicted unacceptable forced expiratory volume in 1 second (FEV 1) and excessively variable FEV 1 and forced vital capacity (FVC). Only participant characteristics predicted unacceptable FVC. Feedback to technicians reduced test failure for FEV 1 by half and excessive within-session variability by one-third. In the reproducibility study, coefficients of variation for FEV 1 and FVC were 3%. Epidemiological studies can achieve standards of between-session reproducibility for spirometry comparable to levels reported by pulmonary function laboratories. Performance feedback to technicians improves the level of minimally acceptable spirometry, and within-session reproducibility. Public Health(2000) 114, 353–360

Improving the quality of spirometry in an epidemiological study The Renfrew–Paisley (Midspan) family study

Population studies in Britain and elsewhere report deficiencies in quality of pulmonary function measurements. Methods were tested to improve the standardisation of spirometry in an epidemiological study. The spirometer provided visual feedback about acceptability and reproducibility to American Thoracic Society (ATS) standards. After 14 weeks technicians (research nurses) were given feedback and further training. Measurements were repeated in a 5% sample. Participant characteristics and technical factors (technician and technician feedback) predicted unacceptable forced expiratory volume in 1 second (FEV1) and excessively variable FEV1 and forced vital capacity (FVC). Only participant characteristics predicted unacceptable FVC. Feedback to technicians reduced test failure for FEV1 by half and excessive within-session variability by one-third. In the reproducibility study, coefficients of variation for FEV1 and FVC were 3%. Epidemiological studies can achieve standards of between-session reproducibility for spirometry comparable to levels reported by pulmonary function laboratories. Performance feedback to technicians improves the level of minimally acceptable spirometry, and within-session reproducibility. Public Health(2000) 114, 353–360

Changes in Forced Expiratory Volume in One Second and Peak Expiratory Flow Rate across a Work Shift among Unexposed Blue Collar Workers

Pre- and postshift spirometry was obtained on 1,113 blue collar workers employed at 35 work sites judged to have no hazardous occupational respiratory exposures on the basis of inspection visits and environmental sampling. In addition to spirometry, a standardized questionnaire was administered by trained personnel. A study population of 944 remained after exclusion of workers for incomplete demographic data and/or spirometry with poor within-session reproducibility, i.e., greater than or equal to 10% variability in the two largest values of either FVC and/or FEV1. Overall mean values of changes across the work shift in FEV1 and peak expiratory flow rate (PEFR) were -0.8% (-0.04 L) and +2.1% (+0.13 L/s), respectively. Standard deviations for these across-shift changes were 5.8% (0.19 L) and 13.2% (1.19 L/s) for FEV1 and PEFR, respectively. In univariate analyses, mean values of across-shift changes were not statistically related to age, race, sex, smoking status, work shift, or FEV1/FVC ratio. However, variability (i.e., standard deviation) of across-shift changes were significantly related to some of these factors. These observations provide a basis for interpreting results of occupational respiratory morbidity surveys involving measurement of changes in FEV1 and/or PEFR across a work shift.