Low Energy Ultra-high Resolution Research Articles

IMPROVING THE QUANTIFICATION ACCURACY OF Tc-99m MIBI DUAL-PHASE PARATHYROID SPECT/CT: A MONTE CARLO SIMULATION STUDY

Objective: Quantitative parathyroid SPECT imaging is a technique used to assess Primary hyperparathyroidism that may have potential in the identification and differentiation of parathyroid lesions as well as the estimation of disease severity. Studying the effect of data acquisition parameters on the quantification error is important for maximizing the accuracy of this diagnostic technique. In this study we examine the effects of different data acquisition parameters, namely the type of collimator, scatter correction status and reconstruction iteration number on the quantification accuracy using computer simulation. Methods: The SIMIND Monte Carlo Simulation and CASToR iterative reconstruction program was used to simulate a commercially available SPECT camera (Siemens Symbia Intevo Gamma Camera) with a crystal size of 29.55cm and 128x128 matrix size. A digital cylindrical phantom filled with water was constructed. A 0.36 cm radius spherical adenoma filled with a uniform 1MBq radioactivity is placed within the phantom. Low-Energy High Resolution (LEHR) and Low Energy Ultra High Resolution (LEUHR) collimator models are tested. Along with the presence of Scatter correction and differing iteration numbers (x16, x32). An image FOV based calibration method was used to gather quantitative information and checked against the input radioactivity. Results: The presence of scatter correction caused a 15-20% relative improvement in quantification accuracy. The optimal number of iterations produced a 10% relative improvement. Overall, accuracies as good as 7% in estimated activity concentration could be observed. Conclusion: The optimization of parameters can provide a significant improvement in quantification accuracy.

Assessment of SPECT images using UHRFB and other low-energy collimators in brain study by Hoffman phantom and manufactured defects

The performance of collimators was investigated using low-energy high-resolution (LEHR) and low-energy ultra-high-resolution (LEUHR) collimators in SPECT system to study the brain physiology by injecting 99mTc-HMPAO radionuclide. Ultra-high-resolution fan beam (UHRFB) images were compared to other low-energy collimator images by constructed defects embedded into Hoffman brain phantom as lateral, deepness and metastasis designs with slices of Perspex. The defects were constructed by CNC machine as circular slices and ring flaws ranging in size from 2 to 16 mm to detect low-concentration regions. The data acquisition was done in tomographic mode with minimum radii and different matrix sizes, data acquisition time and number of projections. The collected data were reconstructed using two methods, filtered backprojection and ordered subset expectation maximization (OSEM). By two radiologists and via thallium and V-shaped markers, the minimum diameters of the constructed flaws inside the abnormal area of the brain phantom were diagnosed to 4.0 ± 0.4, 6.0 ± 0.7 and 8.0 ± 0.9 mm for UHRFB, LEUHR and LEHR, respectively. In OSEM method, the desirable ranges of the filter parameters were 4–8 iterations and 2–4 subsets for FB collimator. The outcomes showed that FB collimator provides the better resolution in axial, coronal and sagittal views using brain perfusion phantom and data from eight patients on tinnitus disease. The UHRFB with converging geometry confirmed the better detection of defect regions due to the lowest ratio of cold/background counts. This study may be useful for early detection of disease transference, monitoring of treatment response and disease progression. A CNC machine was used to make disks for Hoffman brain phantom as metastases and ring defects in evaluation of SPECT images.

Simultaneous fluoroscopic and nuclear imaging: impact of collimator choice on nuclear image quality.

X-ray-guided oncological interventions could benefit from the availability of simultaneously acquired nuclear images during the procedure. To this end, a real-time, hybrid fluoroscopic and nuclear imaging device, consisting of an X-ray c-arm combined with gamma imaging capability, is currently being developed (Beijst C, Elschot M, Viergever MA, de Jong HW. Radiol. 2015;278:232-238). The setup comprises four gamma cameras placed adjacent to the X-ray tube. The four camera views are used to reconstruct an intermediate three-dimensional image, which is subsequently converted to a virtual nuclear projection image that overlaps with the X-ray image. The purpose of the present simulation study is to evaluate the impact of gamma camera collimator choice (parallel hole versus pinhole) on the quality of the virtual nuclear image. Simulation studies were performed with a digital image quality phantom including realistic noise and resolution effects, with a dynamic frame acquisition time of 1 s and a total activity of 150 MBq. Projections were simulated for 3, 5, and 7 mm pinholes and for three parallel hole collimators (low-energy all-purpose (LEAP), low-energy high-resolution (LEHR) and low-energy ultra-high-resolution (LEUHR)). Intermediate reconstruction was performed with maximum likelihood expectation-maximization (MLEM) with point spread function (PSF) modeling. In the virtual projection derived therefrom, contrast, noise level, and detectability were determined and compared with the ideal projection, that is, as if a gamma camera were located at the position of the X-ray detector. Furthermore, image deformations and spatial resolution were quantified. Additionally, simultaneous fluoroscopic and nuclear images of a sphere phantom were acquired with a physical prototype system and compared with the simulations. For small hot spots, contrast is comparable for all simulated collimators. Noise levels are, however, 3 to 8 times higher in pinhole geometries than in parallel hole geometries. This results in higher contrast-to-noise ratios for parallel hole geometries. Smaller spheres can thus be detected with parallel hole collimators than with pinhole collimators (17 mm vs 28 mm). Pinhole geometries show larger image deformations than parallel hole geometries. Spatial resolution varied between 1.25 cm for the 3 mm pinhole and 4 cm for the LEAP collimator. The simulation method was successfully validated by the experiments with the physical prototype. A real-time hybrid fluoroscopic and nuclear imaging device is currently being developed. Image quality of nuclear images obtained with different collimators was compared in terms of contrast, noise, and detectability. Parallel hole collimators showed lower noise and better detectability than pinhole collimators.

Importance of the choice of the collimator for the detection ofsmall lesions in scintimammography: a phantom study

99mTc methoxyisobutylisonitrile planar scintimammography (SMM) is mostly performedusing low-energy high-resolution (LEHR) parallel collimators. We studiedwhether using a different collimator could improve the detection of small(<1.5 cm) lesions for which SMM sensitivity is poor. Thirty fourbreast phantom configurations were considered, either with hot spheressimulating lesions or without any spheres. For each configuration, fourplanar acquisitions were performed using LEHR, low-energy ultrahigh-resolution (LEUHR), high-resolution fan-beam (HRFB) and ultrahigh-resolution fan-beam (UHRFB) collimators. Images corresponding to the20% and 10% energy windows and to the Jaszczak subtraction werecalculated. A database including 156 borderline images was derived. Aftertraining, 10 observers scored the images for the presence of a sphere. Theperformances in sphere detection were studied using receiver operatingcharacteristic (ROC) analysis. For all types of image, the area under theROC curve was highest with the UHRFB collimator and lowest with either theLEUHR or the HRFB collimator. For the 10% energy window imagesconventionally used in SMM, the detection sensitivities averaged 91%,73%, 60% and 55% for the UHRFB, LEHR, HRFB and LEUHR collimatorsrespectively, for the same specificity of 64%. We conclude that detectionof small tumours in planar SMM might be significantly improved by using aUHRFB collimator instead of an LEHR collimator.

DMSA-scintigraphy in paediatrics: Is the evaluation of the geometric mean necessary for the calculation of the differential renal function?

SummaryFor assessment of differential renal function (PF) by means of static renal scintigraphy with Tc-99m-dimer-captosuccinic acid (DMSA) the calculation of the geometric mean of counts from the anterior and posterior view is recommended. Aim of this retrospective study was to find out, if the anterior view is necessary to receive an accurate differential renal function by calculating the geometric mean compared to calculating PF using the counts of the posterior view only. Methods: 164 DMSA-scans of 151 children (86 f, 65 m) aged 16 d to 16 a (4.7 ± 3.9 a) were reviewed. The scans were performed using a dual head gamma camera (Picker Prism 2000 XP, low energy ultra high resolution collimator, matrix 256 x 256,300 kcts/view, Zoom: 1.6-2.0). Background corrected values from both kidneys anterior and posterior were obtained. Using region of interest technique PF was calculated using the counts of the dorsal view and compared with the calculated geometric mean [SQR(Ctsdors x Ctsventr]. Results: The differential function of the right kidney was significantly less when compared to the calculation of the geometric mean (p&lt;0.01). The mean difference between the PFgeom and the PFdors was 1.5 ± 1.4%. A difference &gt; 5% (5.0-9.5%) was obtained in only 6/164 scans (3.7%). Three of 6 patients presented with an underestimated PFdors due to dystopic kidneys on the left side in 2 patients and on the right side in one patient. The other 3 patients with a difference &gt;5% did not show any renal abnormality. Conclusion: The calculation of the PF from the posterior view only will give an underestimated value of the right kidney compared to the calculation of the geometric mean. This effect is not relevant for the calculation of the differntial renal function in orthotopic kidneys, so that in these cases the anterior view is not necesssary. However, geometric mean calculation to obtain reliable values for differential renal function should be applied in cases with an obvious anatomical abnormality.

Reducing the influence of the partial volume effect on SPECT activity quantitation with 3D modelling of spatial resolution in iterative reconstruction

Quantitative parameters such as the maximum and total counts in a volume are influenced by the partial volume effect. The magnitude of this effect varies with the non-stationary and anisotropic spatial resolution in SPECT slices. The objective of this investigation was to determine whether iterative reconstruction which includes modelling of the three-dimensional (3D) spatial resolution of SPECT imaging can reduce the impact of the partial volume effect on the quantitation of activity compared with filtered backprojection (FBP) techniques which include low-pass, and linear restoration filtering using the frequency distance relationship (FDR). The iterative reconstruction algorithms investigated were maximum-likelihood expectation-maximization (MLEM), MLEM with ordered subset acceleration (ML-OS), and MLEM with acceleration by the rescaled-block-iterative technique (ML-RBI). The SIMIND Monte Carlo code was used to simulate small hot spherical objects in an elliptical cylinder with and without uniform background activity as imaged by a low-energy ultra-high-resolution (LEUHR) collimator. Centre count ratios (CCRs) and total count ratios (TCRs) were determined as the observed counts over true counts. CCRs were unstable while TCRs had a bias of for all iterative techniques. The variance in the TCRs for ML-OS and ML-RBI was clearly elevated over that of MLEM, with ML-RBI having the smaller elevation. TCRs obtained with FDR-Wiener filtering had a larger bias than any of the iterative reconstruction methods but near stationarity is also reached. Butterworth filtered results varied by 9.7% from the centre to the edge. The addition of background has an influence on the convergence rate and noise properties of iterative techniques.