Biomedical subjects
L Mortelmans
Publications and source records attributed to L Mortelmans.
Evaluation of small-bowel transit for solid and liquid test meal in healthy men and women.
Evaluation of severe functional gastrointestinal motility disorders requires an investigation of the entire gastrointestinal tract. This should be possible with a single radionuclide imaging study. The purpose of this study was (1) to define normal values of small-bowel transit in men and women and (2) to assess a possible difference between gender or test meal, since it has been shown that women have slower gastric emptying than men, and gastric emptying of solids is slower than liquids. A standard gastric-emptying test for a solid (technetium-99m sulphur colloid, 230 Kcal) and liquid (indium-111 DTPA water) test meal was performed in 12 healthy male and 12 healthy female volunteers. After 135 min, the volunteer was placed in the supine position for static imaging of the abdomen every 15 min for 6 h. Decay and crossover-corrected geometric mean gastric-emptying data were fit to a modified power exponential function to determine the 10% stomach emptying time for solids and liquids separately. An ROI was drawn around the caecum and ascending colon to determine the arrival time of at least 10% of the solid and liquid test meal. Ten percent small-bowel transit time (10% SBTT) and orocaecal transit time (OCTT) were calculated. The OCTT for males and females, respectively for solids and liquids, are 294.6 +/- 18.8; 301.3 +/- 24.5; 294.6 +/- 18.8 and 301.3 +/- 24.5 min. The 10% SBTT for males and females, respectively for solids and liquids, are 280.3 +/- 18.4; 280.6 +/- 24.0; 288.2 +/- 18.9 and 297.4 +/- 24.4 (mean +/- SEM) min. We observed a simultaneous transfer of solids and liquids from the terminal ileum to caecum (correlation coefficient 0.90). There is no statistically significant difference in SBTT between gender or solids and liquids. In contrast to the gastric-emptying time, the SBTT of solids and liquids were not significantly different nor was a gender difference found. Determination of the OCTT seems to be the simplest and most accurate approach to measure SBTT. Since ileocaecal transfer occurs as a bolus phenomenon, a 111In-labelled test meal can also be used for the determination of colon transit in a single imaging study protocol.
Regional brain activity during shape recognition impaired by a scopolamine challenge to encoding.
In the present positron emission tomography (PET) study, we examine the effect of a scopolamine-induced challenge to encoding upon the pattern of regional cerebral blood flow during recognition of a list of abstract visual shapes 3 days after encoding of these shapes. This study was conducted to test hypotheses concerning the fusiform and thalamic contributions to object recognition arising from a previous imaging study of impaired recognition. In that study, we demonstrated that activity in the fusiform cortex and the thalamus during shape recognition was modulated by memory challenges. These memory challenges included, on one hand, impaired storage as a consequence of diazepam administration during encoding, and, on the other hand, impaired retrieval caused by a perceptual challenge. Activation in the fusiform cortex decreased during impaired recognition, irrespective of the type of challenge. In contrast, thalamic activation increased only when the recognition deficit resulted from impaired memory storage. Based on these results, we hypothesized that fusiform activation during recognition reflects the matching of an incoming stimulus with a stored one, whereas thalamic activation reflects retrieval attempts. These hypotheses would receive considerable support if scopolamine, which also impairs memory storage, induced similar modulations of fusiform and thalamic activation. In the present study, we observed that a scopolamine challenge to encoding does indeed modulate the activity in the very same regions that were previously modulated by a diazepam challenge. Hence, a similar memory deficit, although primarily effected through different neurochemical pathways, was paralleled by a similar modulation of activity in the same set of nodes in the shape recognition network. In the fusiform cortex, scopolamine decreased recognition-related activity, as did the sensory challenge of retrieval. Furthermore, covariate analysis demonstrated that the level of fusiform activity linearly correlates with behavioural performance. In the thalamus, activation increased following impaired encoding. This is in accordance with the idea that enhanced thalamic activity reflects increased effort expended in retrieval. In addition, in the intraparietal sulcus, differential activation also increased following impaired memory storage, possibly reflecting enhanced visuospatial attention in an effort to compensate for impaired performance.
Brain activity underlying stereotyped and non-stereotyped retrieval of learned stimulus-response associations.
When humans retrieve learned stimulus-response associations in a stereotyped manner the necessary brain structures may differ from those required when the same associations must be retrieved and adapted to new circumstances. We tested this hypothesis by means of tasks that resembled those employed in monkeys, using positron emission tomography (PET). Stimuli consisted of abstract two-dimensional shapes. Stereotyped retrieval of learned stimulus-response associations was studied by the use of a concurrent discrimination task with fixed pairing. This was contrasted with conditions requiring retrieval and adaptation of learned associations: forced-choice recognition, response reversal and concurrent discrimination with random pairing. Visuomotor control, passive viewing and fixation conditions were also included. During concurrent discrimination with fixed pairing, the left lower precentral gyrus and rostral anterior cingulate demonstrated higher blood flow levels in comparison with recognition, concurrent discrimination with random pairing, and to a lesser degree, response reversal. In the left lower precentral gyrus these blood flow levels were also higher in comparison with control conditions. Conversely, during recognition, concurrent discrimination with random pairing and reversal, a single region within the right inferior frontal gyrus demonstrated higher blood flow levels in comparison with concurrent discrimination with fixed pairing and control conditions. This right inferior frontal gyrus activation did not depend on the need for active familiarity judgements or response inhibition. To conclude, the left lower precentral gyrus is more active during stereotyped retrieval of learned stimulus-response associations and the right inferior prefrontal cortex is more active when a learned stimulus-response association must be retrieved and adapted to new circumstances.
New arguments for a vasculitic nature of polymyalgia rheumatica using positron emission tomography.
OBJECTIVE: To study the possible contribution of fluorodeoxyglucose (FDG)-positron emission tomography (PET) in the diagnosis of giant cell arteritis and polymyalgia rheumatica. METHODS: A consecutive case series consisting of five patients with polymyalgia rheumatica, six patients with temporal arteritis and 23 age-matched patients with other inflammatory conditions were evaluated with FDG-PET. Studies were performed before therapy with steroids was started. RESULTS: A total of 4/6 patients with giant cell arteritis and 4/5 patients with polymyalgia had increased FDG uptake in their thoracic vessels, compared to 1/23 controls (P < 0.001). Increased vascular FDG uptake in the upper legs was seen in 8/11 patients with giant cell arteritis or polymyalgia compared to 8/23 control patients (P < 0.05), and in the lower legs in 6/11 patients compared to 6/23 controls (P = not significant). CONCLUSIONS: FDG-PET scan is the first non-invasive technique which may indicate large-vessel vasculitis and which can show its extension throughout the body. It strongly suggests that polymyalgia rheumatica is a form of vasculitis.
Simultaneous maximum a posteriori reconstruction of attenuation and activity distributions from emission sinograms.
In order to perform attenuation correction in emission tomography an attenuation map is required. We propose a new method to compute this map directly from the emission sinogram, eliminating the transmission scan from the acquisition protocol. The problem is formulated as an optimization task where the objective function is a combination of the likelihood and an a priori probability. The latter uses a Gibbs prior distribution to encourage local smoothness and a multimodal distribution for the attenuation coefficients. Since the attenuation process is different in positron emission tomography (PET) and single photon emission tomography (SPECT), a separate algorithm for each case is derived. The method has been tested on mathematical phantoms and on a few clinical studies. For PET, good agreement was found between the images obtained with transmission measurements and those produced by the new algorithm in an abdominal study. For SPECT, promising simulation results have been obtained for nonhomogeneous attenuation due to the presence of the lungs.
Additional value of whole-body positron emission tomography with fluorine-18-2-fluoro-2-deoxy-D-glucose in recurrent colorectal cancer.
PURPOSE: To assess the additional value of the whole-body [18F]-2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) scan as a staging modality complementing conventional diagnostic methods (CDM) in patients suspected of having recurrent colorectal adenocarcinoma. PATIENTS AND METHODS: In 103 patients, the discordances between FDG-PET and CDM results were identified and related to the final diagnosis obtained by histopathology or clinical follow-up (> 1 year). All FDG-PET studies were reviewed with full knowledge of the CDM findings. RESULTS: In a region-based analysis, discordances between CDM and FDG-PET findings were found in 40 of 412 regions (10%). In these, FDG-PET had additional diagnostic value in 14 of 16 locoregional, six of seven hepatic, seven of eight abdominal, and eight of nine extra-abdominal regions. In a patient-based analysis, CDM categorized a subgroup of 60 patients as having resectable recurrent disease limited to the liver (n = 37) or locoregional region (n = 23). In 13 of these patients, there were discordant FDG-PET findings, detecting additional tumor sites in nine patients and excluding disease in three patients and yielding an additional diagnostic value in 20% of the patients. A second subgroup consisted of 13 patients with inconclusive CDM findings (n = 5) or with elevated plasma carcinoembryonic antigen levels and an otherwise negative conventional work-up (n = 8). In these patients, FDG-PET results were correct in eight of nine discordances, yielding a positive additional diagnostic value in 62% of the patients. CONCLUSION: Whole-body FDG-PET can have a clear impact on the therapeutic management in the follow-up of patients with colorectal cancer.
Nuclear cardiology, Part IV: Viability.
After reading Part IV of this series of nuclear cardiology articles, the reader should be able to describe: (a) the differences between SPECT and PET techniques; (b) the various radiopharmaceuticals and imaging protocols used for detecting viability with SPECT; (c) the different radiopharmaceuticals and imaging protocols used for detecting viability with PET; and (d) the imaging patterns observed after reconstructing myocardial images.
Validation of the lactose-[13C]ureide breath test for determination of orocecal transit time by scintigraphy.
UNLABELLED: The breath test using oral administration of a 13C-labeled substrate, lactose-ureide (LU), to measure orocecal transit time (OCTT) was validated against 99mTc-scintigraphy. Although LU is not absorbed in the human small intestine, colonic bacteria readily metabolize LU, producing 13C-labeled CO2. The time at which 13CO2 appears in breath corresponds to the OCTT. METHODS: Twenty-two healthy volunteers ingested a meal labeled with 99mTc and 13C-LU. Scintigraphy was performed over 8 h at time intervals of 10 or 15 min. OCTT with scintigraphy was defined as the time at which at least 10% of the label had entered the colon. Breath samples were obtained every 10-15 min for 10 h and measured by isotope ratio mass spectrometry. OCTT was defined as the time of first significant increase above baseline. The results were compared using correlation and Altman-Bland statistics. RESULTS: OCTT results from scintigraphy (mean OCTT = 283+/-53 min) and breath test (mean OCTT = 292+/-58 min) correlated well (r = 0.94). Altman-Bland statistics showed close agreement between scintigraphy and breath test. No significant difference between male and female subjects was observed. CONCLUSION: The breath test using 13C-LU is a valid alternative to scintigraphy techniques for measuring OCTT.
Reduction of contamination risks during clinical studies with technegas.
During patient studies with the Technegas equipment in our department, we regularly detected small to considerable contaminations of the operator and in the area surrounding the apparatus. These contaminations were found to be of different origin: residual activity in the tubing from the apparatus to the patient which diffuses after deconnection, residual activity and small particles of the destroyed carbon crucible in the apparatus which are dispersed during opening of the door of the gas preparation chamber, leakage at the patient site during studies in uncooperative patients and a dysfunctioning valve inside the apparatus. To reduce the contamination risks, we made some adaptations to the apparatus. In the first place, the dysfunctioning valve was replaced. In addition, a powerful air exhaust pump with an efficient filter was installed. It was connected with (1) a newly installed transparent box in front of the door of the gas preparation chamber, (2) a dome on a flexible arm which can be positioned above the patient's face during the examination and (3) a nipple on which the mouthpiece can be placed after the study. After these adaptations, a study showed the absence of measurable contamination on the clothing of the personnel handling the apparatus. Occasionally, considerable contamination was still measured on the gloves worn during filling of the carbon boat with generator eluate, but only small contaminations (up to 9.25 kBq) were measured on the mouthmask worn by the operator during administration of the Technegas. This results in a maximum effective dose equivalent from activity deposited in the lungs of 0.008 microSv per study. The total body dose of the operator from external radiation for one Technegas examination was determined to be 2 microSv. The highest dose rate was measured during filling of the crucible (0.2 mSv/h).
Simple design for rapid self-injection ictal SPET during aura.
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Human brain activity related to speed discrimination tasks.
The regional cerebral blood-flow (rCBF) pattern of the human brain was measured using positron emission tomography (PET) while subjects viewed, detected, judged the speed of a moving random dot pattern (RDP) or compared speeds of successive RDPs. In all four conditions, retinal input was identical. Two additional conditions, continuous presentation of a moving and a stationary RDP, were included to identify human MT/V5 (hMT/V5). Both speed discrimination tasks involved the right cuneus and right lingual gyrus and to a lesser degree the left lingual gyrus and a more anterior lingual region in the right hemisphere. There was, however, little or no differential activity over hMT/V5 during either speed discrimination. Direct comparison of the two speed discrimination tasks revealed higher activity in the right middle fusiform gyrus, a result reminiscent of that obtained in earlier studies using orientation and direction as the attribute to be discriminated. These results confirm that processing in the human visual cortex is task dependent and underscore the role of the middle fusiform gyrus in temporal comparison of simple attributes.
Comparison of total and compartmental gastric emptying and antral motility between healthy men and women.
There is increasing evidence of gender-related differences in gastric emptying. The purpose of this study was first, to confirm the difference in gastric emptying for both solid and liquid test meals between healthy men and women, and secondly, to investigate the origin of this difference by studying regional gastric emptying and antral motility. A standard gastric emptying test with additional compartmental (proximal and distal) evaluation and dynamic imaging of the antrum was performed in 20 healthy women studied during the first 10 days of the menstrual cycle, and in 31 healthy age-matched men. In concordance with previous reports, women had a longer half-emptying time for solids as compared to men (86. 2+/-5.1 vs 52.2+/-2.9 min, P<0.05). In our observations this seemed to be related to a significantly prolonged lag phase and a significant decrease in terminal slope. Dynamical antral scintigraphy did not show a significant difference. The distribution of the test meal within the stomach (proximal vs distal) showed more early proximal retention in women as compared to men. The terminal slope of the distal stomach was significantly lower in women. We did not observe a significant difference in gastric emptying of the liquid test meal between men and women. Gastric emptying of solids is significantly slower in healthy women as compared to men. These findings emphasise the importance of using different normal values for clinical and research purposes in gastric emptying scintigraphy in men and women. The difference could not be explained by antral motility alone. Increased proximal retention and a lower terminal emptying rate in women are observations to be further investigated.
Regions in the human brain activated by simultaneous orientation discrimination: a study with positron emission tomography.
In order to compare regional cerebral activity involved in simultaneous as opposed to successive orientation discrimination, we used positron emission tomography to measure regional cerebral blood flow, in two threefold sets of conditions, in a large number of subjects. The first such triad involved simultaneous orientation discrimination, orientation identification and detection, with all tasks using the same pair of gratings. The second triad consisted of successive orientation discrimination with its corresponding identification and detection tasks. Comparisons between tasks within each triad isolate attention to orientation and, respectively, spatial or temporal comparison. The subtraction of detection from simultaneous discrimination revealed activation of right fusiform, right lingual, left precentral, left cingulate and left temporal cortex, in addition to right insula, cerebellum and left thalamus. Only the fusiform, insular and precentral activations remained when the corresponding identification was subtracted from simultaneous discrimination. In contrast, most of the non-visual activation sites remained when simultaneous discrimination was compared with successive discrimination, which also revealed a left lingual activation. These experiments provide further evidence for task-dependent processing in the human visual system and suggest that the right fusiform cortex is involved in spatial as much as temporal comparisons.
Segmental comparison between coronary angiography and positron emission tomography reveals low predictive value of epicardial flow for viability.
BACKGROUND: The functional significance of the anterograde and retrograde filling of coronaries on angiography is controversial. METHODS AND RESULTS: Eighteen patients with 27 severe lesions (> 85% diameter stenosis) after previous extensive myocardial infarction were selected. The left ventricle was divided into 33 segments for regional comparison of epicardial flow (as assessed by angiography) and tissue perfusion as well as metabolism (as measured by 13NH3- and 18FDG-PET). Viability was defined as normal perfusion (> 80% relative of maximum 13NH3 activity) or mismatch defect (> 1.2 metabolism/flow ratio). A method has been developed to register the 'lesion predicted region', determined on the basis of angiography, in the same polar map as derived from the positron emission tomography data. Distal to the lesion, the anterograde epicardial flow was evaluated by Thrombolysis in Myocardial Infarction (TIMI) criteria (TIMI flow 0-3), and retrograde filling was graded on a 0-3 scale (collateral grade 0-3). TIMI flow grade and retrograde collateral grade in every lesion predicted region segment were summed to indicate the total segmental epicardial flow. Out of the 594 segments, 369 were associated with a severe lesion. Among them, significantly higher average perfusion and metabolic activities were found in segments of good epicardial filling (summed epicardial flow > or = 3) than in the territories of limited epicardial flow (summed score < 3): 65.4 +/- 17% vs 45.6 +/- 10 (P = 0.001%) and 68.6 +/- 16% vs 47.4 +/- 11% (P = 0.0004), respectively. However, when we analysed the predictive value of angiographically detectable good epicardial flow for positron emission tomography viability criteria then the positive predictive value was found to be as low as 0.5, while the negative predictive value was considerably higher (0.82). CONCLUSION: After myocardial infarction, angiographically detectable limited epicardial flow reveals scarred segments while good epicardial contrast filling does not necessarily indicate maintenance of nutritive function.
Iterative reconstruction for helical CT: a simulation study.
Iterative reconstruction algorithms for helical CT are presented. The algorithms are derived from two-dimensional reconstruction algorithms, by adapting the projector/backprojector to the helical orbit of the source, and by constraining the axial frequencies with a Gaussian sieve. Simulations have been carried out and the performance of the iterative algorithms is compared to that of filtered backprojection of synthetic (interpolated) two-dimensional sinograms. The iterative algorithms produce superior bias-noise curves. Axial resolution is superior, but disturbing edge-artefacts are introduced.
Human cerebral activity evoked by motion reversal and motion onset. A PET study.
In this PET study, we have investigated the human brain activity evoked by a visual motion paradigm commonly used to measure motion-related visual evoked potentials (VEPs). Because standard PET activation studies have been performed with motion along four axes, we first determined the pattern of brain activation when motion was restricted to a single axis. Motion back and forward along a single horizontal axis compared with a static condition revealed weak differential activations in the cuneus and the parietal cortex. Human area MT/V5 (middle temporal area) was hardly activated at all in this subtraction. Additional functional MRI experiments proved that MT/V5 activity is significantly higher for motion along four axes than for motion along a single axis. Secondly, we attempted to isolate the pattern of brain activity related to the reversal of motion direction and to the onset of motion, i.e. two transient motion components commonly used in measuring motion-related VEPs. To that end, we added a continuous linear contrast modulation, that reached maximum contrast at reversal or onset of motion, and compared both conditions with a contrast-modulated static or continuous motion condition. Subtraction of the static random dot pattern condition from the single-axis motion reversal condition, both contrast-modulated, revealed three significant activations: the anterior parieto-occipital sulcus, the lateral sulcus and the anterior claustrum. Additional analysis showed that these activations were not due to motion appearance or disappearance, but were due to the combination of motion reversal and contrast modulation. Hence, these activations do not reflect the motion reversal transient per se. In order to isolate a metabolic response to the reversal transient per se, we used a conjunction analysis, which suggests that activity in human MT/V5, the cuneus and a parietal insular region could underlie the motion reversal VEP in our experiments. Subtraction of the static random dot pattern condition from the single-axis motion onset condition, both contrast-modulated, revealed a single significant activation in the posterior cingulate cortex. Although the significance of this activation is unclear, it adds further evidence for the visual function of this region.
Extraskeletal uptake of Tc-99m at subcutaneous injection sites in a diabetic patient.
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