Lattice Boltzmann model for thermal transpiration.

The conventional Navier-Stokes-Fourier equations with no-slip boundary conditions are unable to capture the phenomenon of gas thermal transpiration. While kinetic approaches such as the direct simulation Monte Carlo method and direct solution of the Boltzmann equation can predict thermal transpiration, these methods are often beyond the reach of current computer technology, especially for complex three-dimensional flows. We present a computationally efficient nonequilibrium thermal lattice Boltzmann model for simulating temperature-gradient-induced flows. The good agreement between our model and kinetic approaches demonstrates the capabilities of the proposed lattice Boltzmann method.

Lattice Boltzmann simulation of nonequilibrium effects in oscillatory gas flow.

Accurate evaluation of damping in laterally oscillating microstructures is challenging due to the complex flow behavior. In addition, device fabrication techniques and surface properties will have an important effect on the flow characteristics. Although kinetic approaches such as the direct simulation Monte Carlo (DSMC) method and directly solving the Boltzmann equation can address these challenges, they are beyond the reach of current computer technology for large scale simulation. As the continuum Navier-Stokes equations become invalid for nonequilibrium flows, we take advantage of the computationally efficient lattice Boltzmann method to investigate nonequilibrium oscillating flows. We have analyzed the effects of the Stokes number, Knudsen number, and tangential momentum accommodation coefficient for oscillating Couette flow and Stokes' second problem. Our results are in excellent agreement with DSMC data for Knudsen numbers up to Kn=O(1) and show good agreement for Knudsen numbers as large as 2.5. In addition to increasing the Stokes number, we demonstrate that increasing the Knudsen number or decreasing the accommodation coefficient can also expedite the breakdown of symmetry for oscillating Couette flow. This results in an earlier transition from quasisteady to unsteady flow. Our paper also highlights the deviation in velocity slip between Stokes' second problem and the confined Couette case.

Radioguided occult lesion localisation (ROLL) and sentinel node biopsy for impalpable invasive breast cancer.

AIM: The aim of this study was to simplify the technique of ROLL and sentinel node biopsy without compromising tumour excision and sentinel node biopsy. METHODS: Twenty patients with impalpable primary invasive breast carcinoma underwent an injection of 99mTc-nanocolloid mixed with radiographic contrast medium Iohexol into the centre of the lesion under ultrasound or stereotactic guidance pre-operatively. No guidewire localisation was performed. Under general anaesthesia, a periareolar intradermal/subcutaneous injection of patent blue-V dye was performed. The sentinel node was identified by blue-stained lymphatics and node and a hot spot on the gamma probe. Surgical excision of the primary tumour was then carried out using the gamma probe. RESULTS: In eight of 20 cases an immediate re-excision was carried out and on histological assessment, all 20 patients were clear of invasive disease at the margins. In two patients, in situ disease was present at the margins and a further re-excision was therefore performed. The sentinel node was identified in all cases. In all, five of 20 patients were node positive on routine HE staining. In a further two patients, tumour cells were identified by immunohistochemistry with CAM5.2 antibody. Completion axillary clearance in six patients confirmed that the sentinel node was the only positive node. CONCLUSIONS: This modification of the previously described ROLL technique is feasible and safe and does not compromise tumour excision or sentinel node detection.

Variation in lymphatic function may predispose to development of breast cancer-related lymphoedema.

AIMS: Breast cancer-related lymphoedema (BCRL) remains a common complication of breast cancer treatment. Many features of this condition remain poorly understood, such as why only approximately 25% of women are affected after similar treatment, and the phenomenon of 'sparing', in which regions of an otherwise swollen arm, most commonly the hand, remain unaffected. This study uses dual-isotope lymphoscintigraphy, involving measurement of rate of clearance of radiolabelled protein from a subcutaneous depot and subsequent appearance in blood, to quantify alterations in lymphatic function in women with BCRL, and to further investigate differences between those in whom the hand is involved with swelling and those in whom it is spared. METHODS: Participants received a depot injection of human immunoglobulin G in the dorsum of both hands, labeled with technetium-99m on one side and indium-111 on the other. Rates of clearance from the depot and appearance in venous blood were measured at regular intervals over a 3 h period. RESULTS: A total of 18 women with a history of BCRL were studied. Significant reductions in both depot clearance and venous appearance were observed in the affected arm compared with the unaffected contralateral control. On sub-group analysis, significant differences were also observed between swollen and spared hand groups, both for the affected and unaffected contralateral arm. DISCUSSION: This study, as well as confirming impaired lymphatic function in arms affected by BCRL, also shows underlying variation in lymphatic function in the unaffected contralateral arm, between those with and without hand sparing. This raises the possibility that the risk of developing BCRL may be, in part, pre-determined.

Cerebral neutrophil recruitment, histology, and outcome in acute ischemic stroke: an imaging-based study.

BACKGROUND AND PURPOSE: Evidence now exists for a pathogenic role for neutrophils in acute cerebral ischemia. We have studied the patterns and temporal profile of cerebral neutrophil recruitment to areas of acute ischemic stroke (IS) and have attempted to correlate this with neurological status and outcome. METHODS: Patients with cortical middle cerebral artery (MCA) IS were recruited within 24 hours of clinical onset. Neutrophil recruitment was studied using indium-111 (111In) troponolate-labeled neutrophils, planar imaging, and single-photon emission computed tomography (SPECT). Volume of brain infarction was calculated from concurrent computed tomography (CT). Hematoxylin and eosin sections were obtained postmortem (n=2). Outcome was measured using Barthel, Rankin, and National Institute of Health Stroke (NIHSS) scales. RESULTS: Fifteen patients were studied. Significant 111In-neutrophil recruitment to ipsilateral hemisphere, as measured by asymmetry index (AI), was demonstrated within 24 hours of onset in 9 patients; this response was heterogenous between patients and on repeated measurement attenuated over time. Histologically, recruitment was confirmed within intravascular, intramural, and intraparenchymal compartments. Interindividual heterogeneity in neutrophil response did not correlate with infarct volume or outcome. In an exploratory analysis, neutrophil accumulation appeared to correlate significantly with infarct expansion (Spearman rho=0.66; P=0.03, n=12). CONCLUSIONS: Neutrophils recruit to areas of ischemic brain within 24 hours of symptom onset. This recruitment attenuates over time and is confirmed histologically. While neutrophil accumulation may be associated with either the magnitude or the rate of infarct growth, these results require confirmation in future studies.

Tissue-to-blood transport of radiolabelled immunoglobulin injected into the web spaces of the hands of normal subjects and patients with breast cancer-related lymphoedema.

AIM: The ability to return interstitial protein to central blood is key to the defence against oedema. The aim of this study was to quantify this ability by measuring the rate at which radiolabelled human immunoglobulin (HIgG) accumulated in blood following injection into the subcutis of the hand in normal volunteers and in patients with breast cancer-related lymphoedema (BCRL). METHODS: A total of 37 control subjects (healthy normal volunteers or breast cancer patients prior to treatment) and 18 women with BCRL were studied with dual-isotope lymphoscintigraphy. Each received bilateral subcutaneous depot injection in the dorsal web space of HIgG labelled with Tc-99m on one side and In-111 on the other. Activities remaining at the depot and accumulating in blood were measured at regular intervals for 3 h. Clearance from the depot was exponential and expressed as the rate constant k(depot) (min(-1)). Accumulation in blood was essentially linear and, using an estimate of blood volume based on height and weight, was expressed as the linear constant b(blood) (% administered activity x min(-1)). The time axis intercept of this linear fit was recorded as an index of the minimum time to arrival of radioprotein in blood. The efficiency with which radioprotein that has left the depot (extra-depot activity) is transported into blood [tissue-to-blood (T-B) transport] was quantified (1) as the quotient b(blood)/k(depot), and (2) as a function of time after injection by comparing the total amount of radioprotein in blood at any time with the total amount of radioprotein that was no longer in the depot at the same time. RESULTS: Tc-99m-HIgG and In-111-HIgG behaved similarly and are interchangeable. At all times between 60 and 180 min in controls, about 50% of protein that had left the depot was present in blood. T-B transport was reduced to about 20% in BCRL arms in which the hand was involved in swelling (p < 0.001 versus controls), but remained unchanged in patients in whom the hand was spared. The minimum time to arrival of radioprotein in blood was not reduced in BCRL; on the contrary, there appeared to be a small proportion of injected activity that arrived rapidly in blood in BCRL patients but not in controls. CONCLUSION: We conclude that T-B transport is only impaired in BCRL when radioprotein is injected into swollen tissue. Significant quantities of radioprotein may escape from the arm via local access to blood. Individual variation in this capacity may explain the regional sparing observed in BCRL.

Is it safe to work with iodine-131 if you are pregnant? A risk assessment for nuclear medicine staff involved with cleaning and decontamination.

In the UK, Regulation 8(5) of the Ionising Radiation Regulations 1999 (In: Work with ionising radiation. London: HSE Books, 2000) requires employers to ensure that the dose to the foetus of a pregnant worker is unlikely to exceed 1 mSv. Risk assessments are required which are capable of predicting the total foetal dose. Work involving 131I is a particular problem. Foetal dose coefficients from the maternal intake of 131I for all stages of pregnancy have been published (Phipps AW, Smith TJ, Fell TP, Harrison JD. Doses to the embryo/fetus and neonate from intake of radionuclides by the mother. NRPB contract research report 397/2001. Didcot, Oxon.: National Radiological Protection Board (NRPB), 2001. Available on website www.hse.gov.uk/research/crr_pdf/2001/crr01397.pdf), and range from 0.08 microSv x kBq(-1) at conception to 55 microSv x kBq(-1) at week 35. This paper examines one aspect of work in a nuclear medicine department in which the source of 131I is uncontrolled to determine whether the risk assessment indicates that restrictions should apply to a pregnant member of staff. Following in-patient treatment with 131I, rooms are checked and decontaminated before being decontrolled. Cleaning staff were monitored immediately after the cleaning process with hand-held detectors and by whole-body monitoring. Total body contamination ranged up to 3.2 kBq; after a change of clothing, the maximum remaining activity was 0.68 kBq. Acquired contamination correlated with the total activity administered to the patient. Hand-held monitoring rarely detected contamination. Whole-body monitoring indicated that the levels of contamination encountered could lead to a dose limit for the foetus being exceeded. These levels are very difficult to detect with hand-held monitoring. The conclusion to be drawn is that pregnant staff should be excluded from situations in which accidents could arise, or where the source of 131I is uncontrolled or unpredictable.

A collimator with a magnetic personality?

We report an unusual technical problem with a gamma camera fitted with a pinhole collimator. An unexpected decrease of approximately 20 keV in the energy of the 99mTc photopeak is seen if the (circular) collimator is rotated relative to the camera head. The centreline of the photopeak varied over the range 118-141 keV depending on the orientation of the collimator. The count rate and photopeak width changed concurrently. Image uniformity was severely degraded for lower peak energies. The reason for this behaviour is that the pinhole collimator had become magnetized. The magnetic field was measured and had maximum values of 1.0 mT at the edge and 0.1 mT near the camera face. The magnetic field strongly influenced the response of the photomultiplier tubes. We conclude that acceptance testing of gamma cameras should include a check for collimator magnetization.

A comparison of performance of three gamma camera systems for positron emission tomography.

The development of coincidence positron imaging using a gamma camera should significantly increase PET utilization. This study has compared the performance of three such systems with each other and with an equivalent single photon emission computed tomography (SPECT) measurement. A Carlson phantom, which consisted of a 20 cm diameter cylinder containing areas of uniform activity, hot lesions, cold lesions and orthogonal alternate hot and cold lines, was filled with an activity of 18F chosen to try and best exploit each camera and imaged for a fixed time (27 min). The image quality of 9 mm thick slices in each section of the phantom was compared visually. Several image quality parameters were also compared including line source resolution and noise equivalent count rate. There were considerable differences in PET image quality between the three cameras but all were at least as good as the SPECT image. The full width at half maximum (FWHM) resolution of all systems was similar (approximately 4.5 mm) but the maximum noise equivalent count rates in a 20 cm cylinder were significantly different (6.3, 2.6 and 1.6 kcps) (where cps is counts per second) and correlated with the phantom image quality.

Seven-hour stabilization of 99Tcm-exametazime (HMPAO) for cerebral perfusion.

The objective of this study was to increase the stability of 99Tcm-exametazime and to investigate the effects of relaxing the eluate restrictions imposed by the manufacturer. We added 1800 MBq freshly eluted pertechnetate to 0.5 ml aliquots of stannous-enhanced exametazime followed by the addition of 0.7 mg gentisic acid and 0.5 ml sterile absolute alcohol BP. The radiochemical purity as measured by thin-layer chromatography was maintained at over 80% (range 88-99%, n = 40) for up to 7 h after preparation. High-performance liquid chromatography confirmed that the primary complex was maintained at over 80% (ranges 89-92%) for up to 7 h. In a second series of studies using the first eluate from a newly delivered generator to prepare 99Tcm-exametazime, a radiochemical purity of more than 80% was achieved for up to 7 h (range 88-95%, n = 24). In a third series using a 3-hour-old generator eluate, a radiochemical purity of more than 80% (range 88-93%, n = 18) was achieved for up to 5 h (for logistic reasons, we were unable to continue readings beyond 5 h). These results suggest that the manufacturer's restrictions on the eluate may be relaxed. Clinical validation was performed in a blinded study of 21 patients using single photon emission tomography. Image quality was assessed on the basis of salivary activity, nasal activity and the overall (global) image quality. There was no significant difference between the images obtained using the stabilized exametazime and exametazime prepared without gentisic acid and ethanol (chi 2 = 2.85, P = 0.05). We conclude that stabilization of 99Tcm-exametazime can be achieved for up to 7 h by using gentisic acid and alcohol and that the eluate restrictions may be disregarded.

Stabilization and multidose use of exametazime for cerebral perfusion studies.

The efficient use of exametazime for cerebral blood flow imaging is restricted by the short useful life of the reconstituted kit due to the instability of the primary complex. It is therefore recommended that 99Tcm-exametazime be used within half an hour after preparation allowing only a single patient dose to be prepared from one vial of exametazime. The shelf-life of 'cold' reconstituted exametazime has been extended by means of stannous enhancement. Freshly prepared stannous fluoride solution, 0.8 ml (5.4 micrograms SnF2), was mixed with 0.5 ml (42 micrograms) exametazime solution followed by the addition of up to 1500 MBq pertechnetate. The radiochemical purity of the chelate was 91% (S.D. 3.6%, n = 3). The rate of conversion of the primary complex (kc = 0.012 +/- 0.011 h-1) was considerably slower than the rate of degradation obtained using the recommended method of preparation (kc = 0.17 +/- 0.02 h-1). Radiochemical purity levels greater than 80% were maintained for up to 2.5 h after preparation and the level of free pertechnetate did not exceed 7%. There was only a slight deterioration of the cold reconstituted exametazime on storage of 0.3 +/- 0.1% per day. However, exametazime reconstituted up to 3 weeks previously produced more than 80% purity. The mean radiochemical purity obtained in 22 studies was 90% with a range of 81-98%. Clinical validation was performed in a blinded study of 38 patients using single photon emission computed tomography (SPECT). There was no significant difference between the images obtained using the tin enhancement method of preparation and the manufacturer's method (chi 2 = 3.62, P = 0.16).(ABSTRACT TRUNCATED AT 250 WORDS)

Computer-derived regions of interest for the determination of renal parenchymal transit time.

Renal parenchymal transit time measurements are used in the diagnosis of obstructive nephropathy but parenchymal regions are usually drawn by hand with or without the aid of a functional image. This paper describes three computerized methods for derivation of parenchymal regions from a mean time functional image and compares them with the manual method by processing renogram data from 82 normal, 19 obstructed and 11 dilated nonobstructed kidneys using all four techniques. Receiver-operator characteristic analysis demonstrated the computer methods to be superior to manually drawn regions. The optimum computer method had a sensitivity of 95% and specificity 95% for distinguishing obstructed kidneys from dilated nonobstructed kidneys. The computer method could be readily incorporated into routine renogram analysis programs.

Leg muscle scintigraphy with 99Tcm-MIBI in the assessment of peripheral vascular (arterial) disease.

A technique for using 99Tcm-methoxyisobutylisonitrile (MIBI) to evaluate leg muscle perfusion in the assessment of peripheral vascular disease (PVD) is described and evaluated. The uptake of MIBI in muscle groups is quantified and normalized to whole body activity. Eleven patients with PVD undergoing angiography and nine controls were studied. There was a significant difference in MIBI uptake in the calf (P less than 0.000 01) and thigh (P less than 0.0001) between the two groups on exercise. The technique has a sensitivity of 91% and specificity of 94% for the diagnosis of PVD. The technique can also effectively evauate the severity of disease as shown by significant correlations between exercise calf flow and angiographic severity (P less than 0.05) and Doppler ankle/arm pressure measurements (P less than 0.0005). Single photon emission tomography (SPET) of the calves was also performed in five controls and five patients with PVD. Uptake was significantly reduced in all muscle areas in patients with PVD and, amongst those with PVD, uptake was lower in muscle groups by occluded arteries. The potential role of 99Tcm-MIBI in the assessment of PVD and its advantages over other methods of assessment are discussed.

The influence of tissue depth and composition on the performance of the Lunar dual-energy X-ray absorptiometer whole-body scanning mode.

To assess the performance of the Lunar dual-energy X-ray absorptiometer (DPX) whole-body scanning mode (software version 3.1), a simple phantom was devised. This had known but variable amounts of lard to represent fat, and water to represent fat-free tissue. The bone mineral content of the phantom remained constant and consisted of the Lunar spine phantom to represent the spine/trunk and a slab of aluminium to represent the head. This phantom was scanned using the whole-body mode by the Lunar DPX to determine bone mineral content (BMC), area, bone mineral density (BMD), and body composition in terms of fat and fat-free tissue. The determinations of total tissue mass were very accurate and precise but fat tissue mass was slightly overestimated (103% of calculated value) and lean tissue mass slightly underestimated (98% of calculated value). The spine and head sections of the phantom were scanned individually using the spine mode and hence by addition the total BMC, area, and BMD of the whole phantom were determined. These results were compared to the bone mineral results obtained using the whole-body mode. The whole-body mode gave higher values for BMC and area than spine-mode measurements (at depths above 10 cm). This discrepancy increased with increasing depths of water (140% and 170% respectively of spine-mode value at soft-tissue depths of 22 cm and 15% fat). The values for BMD of the whole phantom tended to decrease with increasing depths of water and were lower than spine-mode values at tissue depths above 12cm.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative performance in vitro and in vivo of Lunar DPX and Hologic QDR-1000 dual energy X-ray absorptiometers.

The measured absolute bone mineral density values of spine and femur and their precision were compared on two dual energy X-ray absorptiometers, the Lunar DPX and the Hologic QDR-1000. There were systematic differences between the two systems, the Lunar DPX always giving a higher bone density value. The ratio of the mean Lunar DPX/Hologic QDR-1000 bone density measurements obtained in vivo was 1.13 g/cm2 for spine (L2-L4) and 1.20-1.43 g/cm2 for femur measurements. For both systems, short- and long-term precision (coefficient of variation) was below 0.5% for spine in vitro measurements and below 1.5% for neck of femur in vitro measurements. Precision of in vivo measurements was less good, especially for femur measurements. The coefficient of variation of spine measurements was dependent on bone density and deteriorated with decreased bone mineral density and increased body thickness.

99Tcm-exametazime-labelled leucocytes: effect of volume and concentration of exametazime on labelling efficiency, and clinical protocol for high efficiency multi-dose radiolabelling.

We have investigated the effect of volume and concentration of exametazime on the labelling efficiency of 99Tcm-exametazime-labelled leucocytes. The first study examined the effect of varying the volume of exametazine solution whilst the concentration remained constant. A vial of Ceretec (Amersham Ltd plc) was reconstituted with sodium chloride injection BP. Aliquots of 0.25-2.0 ml were removed, added to sodium pertechnetate injection BP and incubated with 2 x 10(7)-5 x 10(7) leucocytes from 25 ml blood. The labelling efficiency decreased from 65 +/- 10% S.D. (0.25 ml) to 45 +/- 8% (2.0 ml) (n = 4). In a second study different concentrations of exametazime solution were used whilst the volume remained constant. A vial of Ceretec was reconstituted with sodium chloride injection BP. Aliquots of 25-200 micrograms were removed, made up to a fixed volume of 0.6 ml, added to pertechnetate and incubated with the plug of leucocytes as before. The labelling efficiency decreased as the concentration of ligand decreased. Thus for 200 micrograms/0.6 ml the labelling efficiency was 64 +/- 5% and for 25 micrograms/0.6 ml the labelling efficiency was 43 +/- 18% (n = 4). Clinical studies were performed using 50 ml blood from patients with a wide range of inflammatory disorders including inflammatory bowel disease, abdominal abscess and vasculitis. The concentration of ligand used was 83 micrograms/0.25 ml. The labelling efficiency was found to be 82 +/- 7% (n = 36).

Does Fourier phase shift correlate with conduction delay in bundle branch block?

Fourier analysis of radionuclide ventriculography is adept at qualitatively demonstrating interventricular conduction delay in bundle branch block. In this study of eighteen patients, there is a considerable individual variation when the phase delay is expressed as an absolute conduction delay (milliseconds). Much of this variability persists after curve representation by the Fourier function has been optimized. It is suggested that this variability is due to differences in the shape of the right and left ventricular time-activity curves, reflecting differences in contraction and relaxation in the two ventricles. Such differences may be more pronounced in some subjects than others. These results suggest that absolute conduction delay cannot be reliably achieved by this method.