Three-dimensional reconstruction: methods of improving image registration and interpretation

(i) Image registration. The use of serial images for computerised three-dimensional reconstruction necessitates the inclusion of three separate sources of information at the stage of data input. These are (i) artificial registration points or fiducials, (ii) a calibration scale and (iii) an outline of each slab of the section to be included in the reconstruction. Most traditional methods rely on the production of drawings of the contours of the structure under investigation which also include both registration points and a calibration scale. We report on a method which considerably reduces the time involved at this labour intensive stage of reconstruction and in addition allows subsequent reconstructions of different structures to be performed without new drawings. Use is made of computerised alignment of tissue sections and the production of composite photomicrographs of both the tissue under investigation and an accurately registered stage micrometer scale. (ii) Improving image interpretation. Images derived from computerised three-dimensional reconstruction can be affected by the number of coordinates used to form the contour of each slice of a structure and by the number of slices that are used to construct the final model. Too little or too much data can considerably reduce the ability of the observer to interpret accurately the image generated by the computer. We report on a feature-based method which enables the experimenter to assess objectively the amount of data required in the two-dimensional plane, i.e. the number of data points per slice, and the three-dimensional plane, i.e. number of slices per structure, so that optimal reconstructions are generated.     

Three-dimensional CT scan of hemimandibular hyperplasia: case report

Transient absorption spectra of adenine, adenosine and 2'-deoxyadenosine 5'-monophosphate (dAMP) arising from 248 nm laser flash photolysis using acetone as a photosensitizer have been observed. The intermediates recorded are assigned to the excited triplet states and dehydrogenated radicals of adenine and its nucleoside and nucleotide. The excited triplet states of adenine and its derivatives are produced via triplet-triplet excitation transfer and observed for the first time, while the dehydrogenated radicals stemming from the interaction of triplet acetone with adenine and its derivatives via electron transfer through a five-member-ring electron donor-acceptor intermediate. The site of dehydrogenation is suggested to be the hydrogen atom on C(8) of the adenine moiety. Moreover, three sets of kinetic parameters of the triplet decay have been determined. The rate constants of the unimolecular decay (k0), the triplet quenching by the ground state (ksq) and by the triplet quencher Mn2+ (kq) are 1.1 x 10(5), 7.9 x 10(4), 3.7 x 10(4) s-1, 6.9 x 10(8), 8.3 x 10(8), 3.6 x 10(8) dm3 mol-1 s-1 and 4.2 x 10(8), 3.5 x 10(8), 6.0 x 10(8) dm3 mol-1 s-1 respectively for adenine, adenosine and dAMP.     

Validation of an MRI/PET landmark registration method using 3D simulated PET images and point simulations

Three-dimensional (3D) simulated PET images generated from MRI were used to validate a multimodality registration technique based on the identification of internal anatomical landmarks. In addition, point-based simulations were compared with registration datasets acquired over 3 yr of routine use of the technique. Registration errors were found to range from 1.0 mm at the brain centre to 2.8 mm in each dimension at the brain surface.     

Correlation of SPECT and PET cardiac images by a surface matching registration technique

To study the potential role of sympathetic activity in the pathogenesis of arterial hypertension associated with autosomal dominant polycystic kidney disease (ADPKD) and to analyze its relationship with 24-hour blood pressure pattern, plasma catecholamines and 24-hour ambulatory blood pressure monitoring were evaluated in 30 ADPKD hypertensive patients (of which 17 without and 13 with renal failure) and in 50 essential hypertensives. The groups were matched for sex, body mass index, known duration of hypertension, and clinic blood pressure. Plasma catecholamines, determined in resting position, were higher in ADPKD patients without renal failure than in essential hypertensives. Nighttime diastolic blood pressure was higher and the percentage day-night difference in mean blood pressure was lower in hypertensives with ADPKD compared to patients with essential hypertension. Blood pressure was significantly correlated with plasma noradrenaline in ADPKD patients, independently of renal function. No significant differences were observed between ADPKD patients with and without renal failure, with respect to plasma catecholamines, 24-hour daytime and nighttime ambulatory blood pressures and the percentage day-night difference in mean blood pressure.     

Technique to obtain positron emission mammography images in registration with x-ray mammograms

X-ray mammograms reveal abnormal tissue densities, while metabolic images identify regions of abnormal metabolism. Conventional nuclear medicine and radiologic breast images must be acquired at different times with different patient positions making coregistration difficult. Accurate coregistration of metabolic and x-ray images of the breast is likely to be important when acquiring information about the location and diagnosis of suspicious lesions or tumors. Our PEM-1 (positron emission mammography) system detects metabolic activity within the breast. The two planar detectors are integrated into a conventional x-ray mammography unit. This arrangement simplifies the image registration process by allowing a breast metabolic image to be acquired immediately after performing an x-ray mammogram. The patient is not moved between procedures. A coregistration tool has also been developed. A thin plastic sheet with a wire frame protrudes from the side of the upper PEM detector. With the tool positioned over the suspicious area of the breast, a magnified film density image is made using the available x-ray equipment. A radio-opaque rectangular outline of the wire frame is visible on the film image. During a positron emission metabolic scan, detectors acquire a 49 x 59 mm2 image of the same region. The PEM detectors can be positioned anywhere along the width of the breast. This provides an image of a particular region of interest. Several contiguous images may be combined to provide a complete scan.     

PET scan predicts recovery of left ventricular function after coronary artery bypass operation

BACKGROUND: Viable but hypocontractile myocardium can show functional improvement after revascularization (hibernation). It is sometimes difficult, however, to predict viability and recovery in patients with severe left ventricular function. This study sought to identify possible predictive factors of recovery of cardiac function after revascularization in patients with three-vessel disease. METHODS: Positron emission tomography (fluoro-18-deoxyglucose uptake for metabolism; nitrogen 13-labeled ammonia for flow) and equilibrium-gated nuclear angiography (for the global ejection fraction) were performed in 59 patients with three-vessel disease before and after undergoing coronary artery bypass grafting. The positron emission tomographic data were expressed as match normal (flow and metabolism normal), mismatch (low flow, high metabolism), match viable (moderate decrease in flow and metabolism), and match necrosis (low flow and metabolism). RESULTS: Stepwise logistic regression analysis showed that only mismatch regions played a significant role in predicting postoperative improvement in function (p = 0.019). There were 1.7 +/- 1.5 mismatch regions in 31 patients who showed an improvement in their ejection fraction (0.47 +/- 0.14 versus 0.58 +/- 0.11; mean +/- standard deviation) versus 0.8 +/- 1.0 mismatch regions (p = 0.017) in patients who did not show recovery. There was more pronounced functional improvement with increasing numbers of mismatch regions, and patients with at least one mismatch region had a high likelihood of recovery (p < 0.001). In patients with a very low preoperative ejection fraction and two or more mismatch regions, there was early significant recovery (0.27 +/- 0.08 versus 0.46 +/- 0.06; p = 0.009). CONCLUSIONS: At least one mismatch region must be present for there to be a postoperative functional benefit. When a low left ventricular ejection fraction is associated with mismatch, early recovery is substantial.     

F-18 FDG whole-body positron emission tomography scan in primary breast sarcoma

Three patients with primary breast sarcoma showed intense F-18 FDG breast uptake on the whole-body scan. In two patients the uptake was irregular and associated with cold foci that corresponded to hypodense lesions noted on the chest CT; these represented areas of pathologically demonstrated tumor necrosis. There was also intense FDG uptake in pulmonary, axillary, and supraclavicular lymph node metastases. All lesions were confirmed by CT scan of the chest. Thus F-18 FDG positron emission tomographic scanning accurately staged the tumors in these two patients, and it documented local recurrence in the third patient. Histopathologic examination showed evidence of a high-grade sarcoma, a primary rhabdomyosarcoma, and a malignant cystosarcoma phyllodes of the breast. Similar to breast carcinoma, F-18 FDG whole-body positron emission tomographic imaging could be useful in diagnosing and staging primary breast sarcomas.     

Three-dimensional positron emission tomography imaging system and its application for medical use

Current positron emission tomography is capable for three dimensional data acquisition and reconstruction (3D PET). The main advantage of 3D PET is its detectability for lower tracer concentrations. The images by a 3D PET have better signal to noise ratios compared to those by conventional 2D PET. This point is especially important for the studies of distributions of ligands for neuroreceptors such as F-18 FDOPA and C-11 YM-01951, since these ligands show low accumulation in brain. Reduction of scanning time is useful as well for patients are permitting extended scanning periods     

Image generation of serotonin synthesis rates using alpha-methyltryptophan and PET

PURPOSE: The objectives of this study were to examine whether preconditioning can decrease ischemic damage to the retina, by electroretinographic assessment of visual function and by histologic examination of retinal structure; to investigate the time course of the effectiveness of preconditioning; and to determine whether protein synthesis is involved. METHODS: Retinal ischemia was produced for 60 minutes in anesthetized Sprague-Dawley rats. Recovery after ischemia was measured by electroretinography for a maximum period of 7 days. Retinal sections that were sliced 1 micron thick were examined 7 days after ischemia. Retinal ischemia for 5 minutes constituted the preconditioning stimulus. To assess the time course of preconditioning, animals first underwent preconditioning and then 60 minutes of ischemia 1, 24, 72, or 168 hours later; or they underwent a 5-minute sham experiment and 60 minutes of ischemia 24 hours later. An additional group of rats received 0.4 mg/kg cycloheximide, the protein synthesis inhibitor, intraperitoneally before preconditioning and underwent 60 minutes of ischemia 24 hours later. RESULTS: In contrast to the nonpreconditioned rats, preconditioned rats had complete recovery of the a- and b-waves compared with preischemic baseline amplitudes, and ischemia-induced histologic damage was completely prevented when preconditioning was performed 24 or 72 hours (but not 168 hours) before ischemia. Separation of preconditioning and 60 minutes of ischemia by 1 hour caused an even greater impairment of functional retinal recovery compared with that seen in sham-preconditioned rats. Severe histologic damage was also noted. Block of protein synthesis by cycloheximide completely attenuated the protective effect of preconditioning. CONCLUSIONS: Preconditioning induces profound retinal tolerance to ischemia in vivo. The absence of a protective effect of preconditioning when there was a 1-hour or a 168-hour separation between the preconditioning stimulus and ischemia and the inhibition of preconditioning by cycloheximide support the hypothesis that a transient change in protein expression is necessary to provide this protection.     

First Hungarian experiences with positron emission tomography (PET) studies. Members of the PET working group

Diagnostic investigations commenced on the 28th of June 1994 in Hungary's and Central Europe's first PET Centre at the University Medical School of Debrecen. The Centre is equipped with a GE 4096 Plus whole body PET scanner. A metabolic tracer, 18F-deoxy-D-glucose (FDG), was used in the investigations. During the first 15 months 249 PET investigations were made in the Centre of which 242 were diagnostic and 7 normal subjects served as control for the patient studies with brain scans. The number of oncological indications (intra- and extracranial tumours, Hodgkin's lymphomas) was n = 105 (43.4% of the 242 diagnostic examinations), neurological investigations (without intracranial tumours) formed the dominant group (n = 117; 48.3%), whereas the number of cardiological indications was 20 (8.3%). The oncological studies included those of intracranial tumours (n = 76; 31.4%); thyroid tumours (n = 9; 3.7%); Hodgkin's lymphomas (n = 7; 2.9%) and other extracranial tumours (n = 13; 5.4%). The distribution of different neurological and psychiatric investigations was as follows: localization of focal epileptogen zone (n = 60; 24.8%); differential diagnosis of dementias (n = 30; 12.4%); exploration of cerebrovascular diseases (n = 10; 4.1%); and other neurological diseases (n = 17; 7.0%). The main objective of the cardiological PET investigations was the exploration of viable myocardium. The present paper overviews both the procedures (including administrative issues, as well) and the results of the first 249 FDG-PET investigations.     

Clinical applications of registration and fusion of multimodality brain images from PET, SPECT, CT, and MRI

The aim was to assess the specificity and functional significance of liver-infiltrating and peripheral blood T cells in chronic hepatitis C. Peripheral blood mononuclear cells hepatitis C virus from 50 of 58 (86.2%) patients with chronic hepatitis C virus infection and 6 of 28 (21.4%) controls showed a proliferative T cell response to at least one of 16 synthetic peptides covering highly conserved regions of the core, envelope (El) and non-structural regions (NS4) of hepatitis C virus. However, six immunodominant peptides were exclusively recognized by the proliferating blood mononuclear cells from 46 patients with chronic hepatitis C virus infection (79.3%). Fine specificity and HLA-restriction were studied with 15 peptide-specific CD4+ T cell lines and 23 T cell clones isolated from liver tissue and peripheral blood of 12 patients with chronic hepatitis C. It was demonstrated that the peptide-specific response of CD4+ T cells was restricted to the presence of autologous accessory cells and HLA-DR and -DP molecules. Eight peptide-specific T cell lines and five T cell clones derived from liver tissue and peripheral blood, released interferon-gamma (200-6600 pg/ml) and tumor necrosis factor-alpha (100-400 pg/ml) and no or little interleukin-4 (< 140 pg/ml) after peptide-specific or mitogeneic stimulation, thus resembling a Th1-like cytokine profile. Patients with active liver disease showed significantly higher proliferative responses to hepatitis C virus core peptides than asymptomatic hepatitis C virus carriers or complete responders to interferon therapy. In conclusion, class II-restricted CD4+ T cell responses to some immunodominant epitopes within the hepatitis core region correlated with disease activity in chronic hepatitis C virus infection. Functionally, liver-infiltrating and peripheral blood T cells released Th1-like cytokines in response to the specific stimulus. Thus, it can be suggested that CD4+ T cells can mediate the pathogenesis of chronic hepatitis C virus induced liver disease.     

Simultaneous acquisition of iodine-123 emission and technetium-99m transmission data for quantitative brain single-photon emission tomographic imaging

The aim of this study was to obtain quantitative iodine-123 brain single-photon emission tomographic (SPET) images with scatter and attenuation correction. We used a triple-headed SPET gamma camera system equipped with fan-beam collimators with a technetium-99m line transmission source placed at one of the focal lines of the fan-beam collimators. Four energy windows were employed for data acquisition: (a) 126-132 keV, (b) 132-143 keV, (c) 143-175 keV and (d) 175-186 keV. A simultaneous transmission-emission computed tomography scan (TCT-ECT) was carried out for a brain phantom containing 123I solution. The triple energy window scatter correction was applied to the 123I ECT data measured by means of the windows (b), (c) and (d) acquired by two detectors. Attenuation maps were reconstructed from 99mTc TCT data measured by means of the windows (a), (b) and (c) acquired by one detector. Chang's iterative attenuation correction method using the attenuation maps was applied to the 123I ECT images. In the phantom study cross-calibrated SPET values obtained with the simultaneous mode were almost equal to those obtained with the sequential mode, and they were close to the true value, within an error range of 5.5%. In the human study corrected images showed a higher grey-to-white matter count ratio and relatively higher uptake in the cerebellum, basal ganglia and thalamus than uncorrected images. We conclude that this correction method provides improved quantification and quality of SPET images and that the method is clinically practical because it requires only a single scan with a 99mTc external source.     

Technetium-94m-teboroxime: synthesis, dosimetry and initial PET imaging studies

Technetium-94m (T1/2 = 53 min) allows the in vivo study of technetium radiopharmaceuticals with positron emission tomography (PET). PET provides a quantitative assay of radioactivity with excellent temporal and spatial resolution, revealing biodistributions that were previously available only through in vitro assay methods. Technetium-94m, produced by the proton irradiation of natural molybdenum on an 11 MeV cyclotron, was extracted with an electrochemical etching technique. Technetium-94m-pertechnetate was prepared to make the myocardial perfusion agent teboroxime in an identical manner as 99mTcO4-. The increased absorbed radiation dose requires a sevenfold reduction in administered activity compared to 99mTc-teboroxime. Eleven clinical PET studies were performed and visually compared to 13N-ammonia. The clearance half-time for 94mTc-teboroxime was approximately 8 min, with a peak myocardial extraction of approximately 3% of the injected dose into a 400-g heart. These results confirm the potential of 94mTc PET for quantitatively studying the pharmacokinetics of new, and old, technetium agents in man.     

Three-dimensional visualization and quantification of the benzodiazepine receptor population within a living human brain using PET and MRI

The purpose of this study was to measure feelings following weaning in women planning employment within 1 year postpartum and to examine the effects of factors related to duration and employment on these feelings. No significant differences in feelings of sadness, anger, guilt, and relief were reported by women who weaned due to mother-led reasons or baby-led reasons or in women who did or did not meet their breastfeeding goal. Women who did not feed their babies as planned when employed, however, felt significantly more sadness/depression and guilt compared to women who achieved their planned method of feeding.     

Positron emission tomography (PET) methodology for small animals and its application in radiopharmaceutical preclinical investigation

Among the more uncommon tumors that may sometimes be encountered in the laryngeal region is the recently described giant cell tumor of the larynx. This lesion is a true neoplasm, presumably of the fibrohistiocytic series. Histologically, it closely resembles the more familiar true giant cell tumor of long bone. The laryngeal giant cell tumors appear, to date, to be nonmetastasizing lesions; it is possible that they may recur locally if incompletely excised (although this remains to be demonstrated). In view of the rarity of these tumors, a tentative diagnosis of such a neoplasm should always prompt consideration of other (more frequently encountered) differential diagnostic possibilities, including cytologically malignant giant cell-rich tumors such as malignant fibrous histiocytoma and sarcomatoid carcinoma.     

Positron emission tomography (PET) and (F-18)-fluorodeoxyglucose in (FDG) in cancerology

Positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) is a scintigraphic imaging technique undergoing a rapid growth in the field of oncology. The constant progress of the detectors, either CDET or PET dedicated cameras, allows to obtain in routine conditions images with a 5 mm spatial resolution. Absolute tracer uptake quantification is also possible, which allows to evaluate objectively therapy efficacy. The mechanisms of FDG tissular accumulation are now better understood. Increase of glycolysis and of transmembrane transport of glucose seems to be at the origin of the high tumorous accumulation of FDG. The main current oncologic application of FDG PET is the diagnosis of malignancy of the isolated pulmonary nodules, with a sensitivity of more than 95%, and in the staging of lung cancer where PET shows higher performances than conventional imaging. The same stands in cutaneous melanoma and for malignancies of the digestive tract, either in colorectal, pancreatic or esophageal localizations. In colorectal cancers, the role of PET has for long being recognized in the differential diagnosis between recurrence and postoperative fibrosis. In the head and neck tumors, FDG also allows to differentiate between recurrence and postradiation necrosis. In lymphoma, the most suitable site for biopsy can be identified on a PET scan and therapy efficacy can also be assessed. In breast cancer, the detection of metastases seems to be possible with FDG. In brain and thyroid cancers, the role of FDG PET remains to be further determined. The low uptake of FDG in prostate cancer metastasis is not in favor of its use in this indication. In conclusion, the indications of FDG PET in oncology are now becoming more precise and it can be expected that clinical PET centers will soon appear in France.