The role of 18F-FDG PET/CT imaging in paediatric Langerhans disease: Case report.

Langerhans cell histiocytosis (LCH) is a haematological disorder, affecting single or multiple organs, characterized by abnormal proliferation of Langerhans cells in children. Accurate tumour delineation (number of lesions, organs involved) is crucial for staging/re-staging, and follow-up (response to therapy). Conventional imaging techniques (computed tomography (CT), magnetic resonance imaging (MRI)) have been employed for initial diagnosis, staging and assessment of response to therapy focusing on the healing effect therapeutic protocols have on the disease. In this case report, whole-body positron emission tomography/computed tomography (PET/CT) was shown either to provide information on the metabolic activity of histiocytes, or identify lesions otherwise asymptomatic. It is clear that PET/CT, combining anatomic and metabolic information, provides data for accurate staging, therapeutic protocol selection and assessment of response to therapy.

Dose optimization of 2D X-ray image acquisition protocols in image-guided radiotherapy.

PURPOSE: In contemporary radiotherapy, patient positioning accuracy relies on kV imaging. This study aims at optimizing planar kV image acquisition protocols regarding patient dose without degrading image quality. MATERIALS AND METHODS: An image quality test-object was placed in-between PMMA plates, suitably arranged to model head or pelvis. Constructed phantoms were imaged using default protocols, the resultant image quality was assessed and the corresponding radiation dose was measured. The process was repeated using numerous kV/mAs combinations to identify those acquisition settings providing images at lower dose than the default protocols but without deterioration in image quality. Default and dose-optimized protocols were then tested on an anthropomorphic phantom and on 51 patients during two successive treatment sessions. Image quality was independently assessed by two readers. Organ and effective doses were estimated using a Monte Carlo simulation software. RESULTS: Low-contrast detectability exhibited a stronger dependence on kV/mAs settings, compared to high-contrast resolution. Dose-optimized protocols resulted in significant dose reductions (anteroposterior-head 48.0 %, lateral-head 30.0 %, anteroposterior-pelvis 28.4 %, lateral-pelvis 27.0 %) compared to the default ones, without compromising image quality. Optimized protocols decreased effective doses by 54 % and 29.6 % in head and pelvic acquisitions, respectively. Regarding image quality, anthropomorphic and patient images acquired using the dose-optimized protocols were subjectively evaluated equivalent to those obtained with the corresponding default settings, indicating that the proposed protocols may be routinely used. CONCLUSIONS: Given the potentially large number of radiotherapy fractions and the pertinent image acquisitions, dose-optimized protocols could significantly reduce patient dose associated with planar imaging without compromising positioning accuracy.

Exploring radiographers' perceptions and knowledge about patient lead shielding: a cross-sectional study in Greece and Cyprus.

The present study aimed to explore radiographers' knowledge, clinical practice and perceptions regarding the use of patient lead shielding in Greece and Cyprus. Qualitative data were analyzed using conceptual content analysis and through the classification of findings into themes and categories. A total of 216 valid responses were received. Most respondents reported not being aware of the patient shielding recommendations issued by the American Association of Physicists in Medicine (67%) or the guidance issued by the British Institute of Radiology (69%). Shielding-related training was generally not provided by radiography departments (74%). Most of them (85%) reported that they need specific guidance on lead shielding practices. Also, 82% of the respondents said that lead shielding should continue to be used outside the pelvic area when imaging pregnant patients. Pediatric patients are the most common patient category to which lead shielding was applied. Significant gaps in relevant training have been identified among radiographers in Greece and Cyprus, highlighting the need for new protocols and provision of adequate training on lead shielding practices. Radiography departments should invest in appropriate shielding equipment and adequately train their staff.

Blood velocity pulse quantification in the human conjunctival pre-capillary arterioles.

Axial red blood cell velocity pulse was quantified throughout its period by high speed video microcinematography in the human eye. In 30 conjunctival precapillary arterioles (6 to 12 microm in diameter) from 15 healthy humans, axial velocities ranged from 0.4 (the minimum of all the end diastolic values) to 5.84 mm/s (the maximum of all the peak systolic values). With the velocity pulse properly quantified, two parameters can be estimated: (1) the average velocity of the pulse during a cardiac cycle AVV (average velocity value) and (2) the magnitude of the pulsation using Pourcelot's resistive index RI. These parameters are important for the estimation of other hemodynamic parameters such as the average volume flow and the average shear stress. The results of this study revealed that the AVV in the human precapillary arterioles ranged between 0.52 and 3.26 mm/s with a mean value for all microvessels of 1.66 mm/s+/-0.11(SE). The RI ranged between 35.5% and 81.8% with a mean value of 53.1%+/-2.2. Quantitative information was obtained for the first time on the velocity pulse characteristics just before the human capillary bed.

The importance of the accuracy of image registration of SPECT images for 3D targeted radionuclide therapy dosimetry.

In this paper, the importance of the accuracy of image registration of time-sequential SPECT images for 3D targeted radionuclide therapy dosimetry is studied. Image registration of a series of SPECT scans is required to allow the computation of the 3D absorbed dose distribution for both tumour sites and normal organs. Three simulated 4D datasets, based on patient therapy studies, were generated to allow the effect of mis-registration on the absorbed dose distribution to be investigated. The tumour sites studied range in size, shape and position, relative to the centre of the 3D SPECT scan. Randomly generated transformations along the x-, y- and z-axes and rotations around the z-axis were employed and the maximum and average absorbed dose distribution statistics, for the tumour sites present, were computed. It was shown that even small mis-registrations, translation of less than 9 mm and rotation of less than 5 degrees might cause differences in the absorbed dose statistics of up to 90%, especially when the size of the tumour is comparable to the induced mis-registration or when the tumour is situated close to the edge of the 3D dataset.

A generalized 4D image registration scheme for targeted radionuclide therapy dosimetry.

An iterative, generalized four-dimensional (4D) method is presented in this paper that allows simultaneous registration of a series of single-photon emission computed tomography (SPECT) scans acquired in the course of a radionuclide therapy or pretherapy tracer study. The method combines temporal information with voxel-based similarity criteria to carry out simultaneous registration of the SPECT scans. A polynomial function was fitted to the maximum counts of each tumor site over the 4D study. Each tumor site was normalized to its maximum on the reference scan, and a template 4D dataset was generated, employing the polynomial fitting and the normalization map. Then, each 3D scan was registered to the corresponding simulated scan, using a 3D similarity criterion. The correlation coefficient (CC), the mutual information (MI), and the sum-of-absolute differences (SAD) similarity criteria were employed. Simulated data, based on a head-neck (131)I-MIBG study, were used to compare the proposed method for 4D registration with sequential 3D registration. Sequential 3D registration resulted in residual registration errors of 3.5 +/- 2.5, 3.2 +/- 2.0, and 7.0 +/- 3.5 mm for the CC, MI, and SAD criteria respectively, whereas the corresponding 4D method gave errors of 2.4 +/- 1.6, 1.9 +/- 1.1, and 5.3 +/- 2.9 mm for the CC, MI, and SAD criteria, respectively. The 4D method was applied to (186)Re HEDP SPECT patient studies and registration was verified by a dual-cursor display tool.

A novel four-dimensional image registration method for radionuclide therapy dosimetry.

A novel method for registering sequential SPECT scans (4DRRT) is described, whereby all sequential scans acquired in the course of a therapy or a pre-therapy tracer study may be registered in one pass. The method assumes that a monoexponential decay function can be fitted to the series of sequential SPECT scans. Multiple volumes, presenting with different decay rates, are fitted with different mono-exponential functions. The MSSE (mean sum of squared errors in the least-squares fit algorithm), over the volume used for registration, is the cost function minimized at registration. Simulated data were used to assess the effect of thresholding, smoothing, noise and the multi-exponential nature of the four-dimensional (4D) SPECT studies on the performance of 4DRRT, resulting in three-dimensional (3D) residual registration errors <3.5 mm. The 4DRRT method was then compared to the following 3D registration methods: the correlation coefficient, the sum of absolute differences, the variance of image ratios and the mutual information. The comparisons, using both simulated and clinical data, were based on the standard deviation of the effective decay time distribution, generated from the registered 4D dataset, and showed that image registration using 4DRRT is simpler and more robust compared to the 3D techniques, especially when multiple tumour sites with different decay rates are present.

RMDP: a dedicated package for 131I SPECT quantification, registration and patient-specific dosimetry.

The limitations of traditional targeted radionuclide therapy (TRT) dosimetry can be overcome by using voxel-based techniques. All dosimetry techniques are reliant on a sequence of quantitative emission and transmission data. The use of (131)I, for example, with NaI or mIBG, presents additional quantification challenges beyond those encountered in low-energy NM diagnostic imaging, including dead-time correction and additional photon scatter and penetration in the camera head. The Royal Marsden Dosimetry Package (RMDP) offers a complete package for the accurate processing and analysis of raw emission and transmission patient data. Quantitative SPECT reconstruction is possible using either FBP or OS-EM algorithms. Manual, marker- or voxel-based registration can be used to register images from different modalities and the sequence of SPECT studies required for 3-D dosimetry calculations. The 3-D patient-specific dosimetry routines, using either a beta-kernel or voxel S-factor, are included. Phase-fitting each voxel's activity series enables more robust maps to be generated in the presence of imaging noise, such as is encountered during late, low-count scans or when there is significant redistribution within the VOI between scans. Error analysis can be applied to each generated dose-map. Patients receiving (131)I-mIBG, (131)I-NaI, and (186)Re-HEDP therapies have been analyzed using RMDP. A Monte-Carlo package, developed specifically to address the problems of (131)I quantification by including full photon interactions in a hexagonal-hole collimator and the gamma camera crystal, has been included in the dosimetry package. It is hoped that the addition of this code will lead to improved (131)I image quantification and will contribute towards more accurate 3-D dosimetry.

Absorbed dose ratios for repeated therapy of neuroblastoma with I-131 mIBG.

Patients undergoing targeted radionuclide therapy (TRT) may receive a series of two or more treatment administrations at varying intervals. However, the level of activity administered and the frequency of administration can vary widely from centre to centre for the same therapy. Tumour dosimetry is seldom employed to determine the optimum treatment plan mainly due to the potential inaccuracies of image quantification. In this work 3D dose distributions obtained from repeated therapies have been registered to enable the dose ratios to be determined. These ratios are independent of errors in image quantification and, since the same target volume can be transferred from one distribution to the next, independent of inconsistencies in outlining these volumes. These techniques have initially been applied to ten sets of I-131 mIBG therapy scan data from five patients, each undergoing two therapies. It was found that where a similar level of activity was administered for the second therapy, a similar tumour dose was delivered, and in two cases where a higher level of activity was administered for the second treatment, a correspondingly higher absorbed dose was delivered. This justifies an approach of administering activities based on individual patient kinetics rather than administering standard activities to all patients.