In-111 DTPA-D-Phe1-octreotide SPECT in a rare case of anorectal small-cell undifferentiated neuroendocrine carcinoma.
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Aged↗
Biomedical subjects
André Constantinesco
Publications and source records attributed to André Constantinesco.
Pinhole SPECT imaging: compact projection/backprojection operator for efficient algebraic reconstruction.
We describe the efficient algebraic reconstruction (EAR) method, which applies to cone-beam tomographic reconstruction problems with a circular symmetry. Three independant steps/stages are presented, which use two symmetries and a factorization of the point spread functions (PSFs), each reducing computing times and eventually storage in memory or hard drive. In the case of pinhole single photon emission computed tomography (SPECT), we show how the EAR method can incorporate most of the physical and geometrical effects which change the PSF compared to the Dirac function assumed in analytical methods, thus showing improvements on reconstructed images. We also compare results obtained by the EAR method with a cubic grid implementation of an algebraic method and modeling of the PSF and we show that there is no significant loss of quality, despite the use of a noncubic grid for voxels in the EAR method. Data from a phantom, reconstructed with the EAR method, demonstrate 1.08-mm spatial tomographic resolution despite the use of a 1.5-mm pinhole SPECT device and several applications in rat and mouse imaging are shown. Finally, we discuss the conditions of application of the method when symmetries are broken, by considering the different parameters of the calibration and nonsymmetric physical effects such as attenuation.
Algorithms↗
Validation of q-ball imaging with a diffusion fibre-crossing phantom on a clinical scanner.
Magnetic resonance (MR) diffusion imaging provides a valuable tool used for inferring structural anisotropy of brain white matter connectivity from diffusion tensor imaging. Recently, several high angular resolution diffusion models were introduced in order to overcome the inadequacy of the tensor model for describing fibre crossing within a single voxel. Among them, q-ball imaging (QBI), inherited from the q-space method, relies on a spherical Radon transform providing a direct relationship between the diffusion-weighted MR signal and the orientation distribution function (ODF). Experimental validation of these methods in a model system is necessary to determine the accuracy of the methods and to optimize them. A diffusion phantom made up of two textile rayon fibre (comparable in diameter to axons) bundles, crossing at 90 degrees , was designed and dedicated to ex vivo q-ball validation on a clinical scanner. Normalized ODFs were calculated inside regions of interest corresponding to monomodal and bimodal configurations of underlying structures. Three-dimensional renderings of ODFs revealed monomodal shapes for voxels containing single-fibre population and bimodal patterns for voxels located within the crossing area. Principal orientations were estimated from ODFs and were compared with a priori structural fibre directions, validating efficiency of QBI for depicting fibre crossing. In the homogeneous regions, QBI detected the fibre angle with an accuracy of 19 degrees and in the fibre-crossing region with an accuracy of 30 degrees .
Anisotropy↗
Assessment of left ventricular perfusion, volumes, and motion in mice using pinhole gated SPECT.
UNLABELLED: Quantitative functional normal data should be a prerequisite before applying SPECT in murine models of cardiac disease. Therefore, we investigated the capability of in vivo pinhole gated SPECT for establishment of a reference database for left ventricular myocardial perfusion, volumes, and motion in normal mice. METHODS: A small-animal dedicated pinhole gamma-camera with a field of view of 17 cm and a focal distance of 12 cm was used with a 1.5-mm pinhole and a 2.5-cm radius of rotation. Phantoms were designed to test spatial resolution and microvolume measurements of accuracy. Eight adult normal mice (CD1) were studied using a heated mixture of air (0.3 L/min) and 1.5%-2.5% isoflurane for anesthesia. For myocardial perfusion, 350-450 MBq of (99m)Tc-tetrofosmin were used in 0.15-0.25 mL. Gated acquisitions (8 or 10 time bins per cardiac cycle) were obtained using a 180 degrees circular arc and 48 anterior projections of 300 R-R intervals. Image reconstruction was done using a specific Algebraic Reconstruction Technique (ART) cone-beam algorithm. For quantification, reconstructed images were processed using standard nuclear medicine software. RESULTS: Millimetric spatial resolution and volume calibration linear relationships (r(2) = 0.99) in the 10- to 100-muL range were obtained in phantoms and used to scale in vivo volume values. In mice, left ventricular perfusion was lower in the apex (65% +/- 6%) versus lateral (72% +/- 5%), inferior (74% +/- 5%), septum (75% +/- 4%), and anterior (74% +/- 2%) walls. The left ventricular ejection fraction was 60% +/- 9%, end-diastolic volume was 50 +/- 8 muL, end-systolic volume was 20 +/- 6 muL, stroke volume was 29.5 +/- 6 muL, and cardiac output was 9.6 +/- 1.6 mL/min. Wall thickening was higher in the apex (47% +/- 12%) versus lateral (30% +/- 9%), inferior (33% +/- 8%), septum (37% +/- 10%), and anterior (33% +/- 10%) walls. CONCLUSION: This work shows that in vivo pinhole gated SPECT can be used for assessment of left ventricular perfusion, volumes, and cardiac function in normal mice.
Animals↗
Laser-polarized xenon nuclear magnetic resonance, a potential tool for brain perfusion imaging: measurement of the xenon T1 in vivo.
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Animals↗
Method to determine in vivo the relaxation time T1 of hyperpolarized xenon in rat brain.
The magnetic polarization of the stable (129)Xe isotope may be enhanced dramatically by means of optical techniques and, in principle, hyperpolarized (129)Xe MRI should allow quantitative mapping of cerebral blood flow with better spatial resolution than scintigraphic techniques. A parameter necessary for this quantitation, and not previously known, is the longitudinal relaxation time (T(1) (tissue)) of (129)Xe in brain tissue in vivo: a method for determining this is reported. The time course of the MR signal in the brain during arterial injection of hyperpolarized (129)Xe in a lipid emulsion was analyzed using an extended two-compartment model. The model uses experimentally determined values of the RF flip angle and the T(1) of (129)Xe in the lipid emulsion. Measurements on rats, in vivo, at 2.35 T gave T(1) (tissue) = 3.6 +/- 2.1 sec (+/-SD, n = 6). This method enables quantitative mapping of cerebral blood flow.
Animals↗
[Sentinel lymph node biopsy with micrometastases in breast cancer: histological data and surgical implications. About a series of 201 axillary dissections after peroperative sentinel node identification].
The benefit of systematic dissection of the non-sentinel lymph nodes (NSLN) in case of micrometastases (> or = 2 mm) in sentinel lymph nodes (SLN) is still being debated. The purpose of this work was to identify, from the histological characteristics of the micrometastases and the primitive tumors out of a series of 201 invasive breast carcinomas, of which 57.2% were pTl, which axillary dissection could be avoided. All cases had axillary dissection after peroperative SLN identification. The SLN were examined after fixation hy HE and immunohistochemical techniques (IHC), over their entire thickness from 2 to 3 mm-thick blocks of tissue and according to levels of histological sections with a spacing of 500 microm. The SLN were metastasized in 87/201 cases (43.3%) and in 29/8 7 cases (33.3%) it concerned micrometastases, 2/3 of which was only detected by IHC. The ability to discover micrometastases was proportional to the number of histological sections analyzed (58.6%, 82.7% and 100% of discovery with 1, 3 and 5 levels per block respectively). In 8/29 cases (27.6%) the NSLN were metastasized and in 6/8 cases it concerned macrometastases (> 2 mm). Taken separately, the characteristics of the tumors (size, histological type, grading, angioinvasion, multifocality), of the micrometastases (HE detection vs IHC detection, size, number) and of the site of injection of the radiotracer (peritumoral versus sub-areolar) did not allow us to isolate a group with micrometastases in the SLN but without metastases in the NSLN. However, the nine pT1 ductal carcinomas without angioinvasion were all NSLN negative. In conclusion, these results show that identification of micrometastases in SLN may influence the surgical decisions of re-excision, and that methodology of the pathological analysis is determinant.
Axilla↗