MRI-guided voxel-based automatic semi-quantification of dopamine transporter imaging.

PURPOSE: Functional imaging with 123I-FP-CIT SPECT suffers from poor spatial resolution resulting in partial-volume effect, which affects the subsequent semi-quantification. Definition of regions of interest for semi-quantification is further subject to user's experience and inter-observer variability. The aim of this work has been to develop an automatic method for definition of volumes of interest and partial-volume correction using patient-specific MRI and providing complete contrast recovery in striatal region. METHOD: The method consists of spatial pre-processing (image segmentation and multi-modality registration), partial-volume correction (performed by region-based voxel-wise technique), and calculation of uptake indices in striatal structures. Anthropomorphic striatal phantom was used to optimize the method and to assess linearity, accuracy, and reproducibility. The method was tested on 58 patient datasets and compared with clinical assessment and BasGan software. RESULTS: The method works automatically. The output is highly linear regarding changing striatal uptake. Complete contrast recovery is achieved using 6.5 mm FWHM. Accuracy is better than 0.15 in terms of RMSE between measured and true uptake indices. Reproducibility is better than 5% for normal uptake ratio. The method outperformed clinical assessment in all measures. With patient data, it provided results closer to BasGan (RMSE 0.9) than to clinical assessment (RMSE 1.9) and fairly correlated with both. CONCLUSION: The proposed method provides complete recovery of striatal contrast under given acquisition and reconstruction conditions. It reduces intra- and inter-observer variability, accurately defines volumes of interest, and effectively suppresses partial-volume effect. It can be reproduced using publicly available software.

Assessment of renal function before contrast media injection: right decisions based on inaccurate estimates.

OBJECTIVES: Information on renal function required before specified radiological examinations with contrast agents is usually obtained through prediction equations using serum creatinine and anthropometric data. The aim of our study was to demonstrate discrepancy between poor prediction and good diagnostic accuracy of glomerular filtration rate (GFR) estimated by prediction equations. METHODS: In 50 patients, reference GFR was measured as plasma clearance of 51-chromium labeled ethylene-diamine-tetraacetic-acid (51Cr-EDTA) and compared with GFR assayed by creatinine clearance (CC) and estimated by Cockcroft-Gault prediction equation (CG). For comparisons, CC and CG were considered as continuous, categorical, and binary variables. Accuracy of the reference GFR prediction was expressed in terms of prediction errors and diagnostic accuracy indices. RESULTS: As continuous variable, CG estimated individual values of GFR with large prediction error exceeding that of CC. As categorical variable, it classified the patient stage of chronic kidney disease (CKD) with medium diagnostic accuracy of 74% (CKD 3) and 62% (CKD 4). As binary variable, CG classified individual patient's GFR below 30 and 60 ml/min/1.73 m2 with good diagnostic accuracy of 80 and 94%, respectively. Performance of other prediction equations did not significantly differ from CG. CONCLUSIONS: Despite large variance and poor prediction accuracy of individual GFR estimates, most of them correctly classified individual patient's GFR below specified level. Results of prediction equations thus should be used and reported exclusively as binary variables, while numerical values of GFR, if required, should be measured by more accurate radionuclide or laboratory methods. KEY POINTS: • Radiological guidelines on contrast media require estimation of glomerular filtration rate to assess kidney function before specified contrast examinations. • Estimated glomerular filtration rate is obtained through prediction equations using serum creatinine and anthropometric data as predictors. • While numerical estimates of glomerular filtration rate are inaccurate (their prediction accuracy is poor), diagnostic accuracy of binary estimates (ability to classify patient's glomerular filtration rate below or above a specified level) is very good.

The SNMMI and EANM practice guideline for renal scintigraphy in adults.

PURPOSE: The Society of Nuclear Medicine and Molecular Imaging (SNMMI) is an international scientific and professional organization founded in 1954 to promote the science, technology, and practical application of nuclear medicine. The European Association of Nuclear Medicine (EANM) is a professional nonprofit medical association that facilitates communication worldwide between individuals pursuing clinical and research excellence in nuclear medicine. The EANM was founded in 1985. SNMMI and EANM members are physicians, technologists, and scientists specializing in the research and practice of nuclear medicine. METHODS: The SNMMI and EANM will periodically define new guidelines for nuclear medicine practice to help advance the science of nuclear medicine and to improve the quality of service to patients throughout the world. Existing practice guidelines will be reviewed for revision or renewal, as appropriate, on their fifth anniversary, or sooner, if indicated. CONCLUSION: Each practice guideline, representing a policy statement by the SNMMI/EANM, has undergone a thorough consensus process in which it has been subjected to extensive review. The SNMMI and EANM recognize that the safe and effective use of diagnostic nuclear medicine imaging requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guideline by entities not providing these services is not authorized.

Improved scatter correction with factor analysis for planar and SPECT imaging.

Quantitative nuclear medicine imaging is an increasingly important frontier. In order to achieve quantitative imaging, various interactions of photons with matter have to be modeled and compensated. Although correction for photon attenuation has been addressed by including x-ray CT scans (accurate), correction for Compton scatter remains an open issue. The inclusion of scattered photons within the energy window used for planar or SPECT data acquisition decreases the contrast of the image. While a number of methods for scatter correction have been proposed in the past, in this work, we propose and assess a novel, user-independent framework applying factor analysis (FA). Extensive Monte Carlo simulations for planar and tomographic imaging were performed using the SIMIND software. Furthermore, planar acquisition of two Petri dishes filled with 99mTc solutions and a Jaszczak phantom study (Data Spectrum Corporation, Durham, NC, USA) using a dual head gamma camera were performed. In order to use FA for scatter correction, we subdivided the applied energy window into a number of sub-windows, serving as input data. FA results in two factor images (photo-peak, scatter) and two corresponding factor curves (energy spectra). Planar and tomographic Jaszczak phantom gamma camera measurements were recorded. The tomographic data (simulations and measurements) were processed for each angular position resulting in a photo-peak and a scatter data set. The reconstructed transaxial slices of the Jaszczak phantom were quantified using an ImageJ plugin. The data obtained by FA showed good agreement with the energy spectra, photo-peak, and scatter images obtained in all Monte Carlo simulated data sets. For comparison, the standard dual-energy window (DEW) approach was additionally applied for scatter correction. FA in comparison with the DEW method results in significant improvements in image accuracy for both planar and tomographic data sets. FA can be used as a user-independent approach for scatter correction in nuclear medicine.

A simple method for determining split renal function from dynamic (99m)Tc-MAG3 scintigraphic data.

PURPOSE: Commonly used methods for determining split renal function (SRF) from dynamic scintigraphic data require extrarenal background subtraction and additional correction for intrarenal vascular activity. The use of these additional regions of interest (ROIs) can produce inaccurate results and be challenging, e.g. if the heart is out of the camera field of view. The purpose of this study was to evaluate a new method for determining SRF called the blood pool compensation (BPC) technique, which is simple to implement, does not require extrarenal background correction and intrinsically corrects for intrarenal vascular activity. METHODS: In the BPC method SRF is derived from a parametric plot of the curves generated by one blood-pool and two renal ROIs. Data from 107 patients who underwent (99m)Tc-MAG3 scintigraphy were used to determine SRF values. Values calculated using the BPC method were compared to those obtained with the integral (IN) and Patlak-Rutland (PR) techniques using Bland-Altman plotting and Passing-Bablok regression. The interobserver variability of the BPC technique was also assessed for two observers. RESULTS: The SRF values obtained with the BPC method did not differ significantly from those obtained with the PR method and showed no consistent bias, while SRF values obtained with the IN method showed significant differences with some bias in comparison to those obtained with either the PR or BPC method. No significant interobserver variability was found between two observers calculating SRF using the BPC method. CONCLUSION: The BPC method requires only three ROIs to produce reliable estimates of SRF, was simple to implement, and in this study yielded statistically equivalent results to the PR method with appreciable interobserver agreement. As such, it adds a new reliable method for quality control of monitoring relative kidney function.

WWSSF - a worldwide study on radioisotopic renal split function: reproducibility of renal split function assessment in children.

PURPOSE: The split or differential renal function is the most widely accepted quantitative parameter derived from radionuclide renography. To examine the intercenter variance of this parameter, we designed a worldwide round robin test. METHODS: Five selected dynamic renal studies have been distributed all over the world by e-mail. Three of these studies are anonymized patient data acquired using the EANM standardized protocol and two studies are phantom studies. In a simple form, individual participants were asked to measure renal split function as well as to provide additional information such as data analysis software, positioning of background region of interest, or the method of calculation. RESULTS: We received the evaluation forms from 34 centers located in 21 countries. The analysis of the round robin test yielded an overall z-score of 0.3 (a z-score below 1 reflecting a good result). However, the z-scores from several centers were unacceptably high, with values greater than 3. In particular, the studies with impaired renal function showed a wide variance. CONCLUSION: A wide variance in the split renal function was found in patients with impaired kidney function. This study indicates the ultimate importance of quality control and standardization of the measurement of the split renal function. It is especially important with respect to the commonly accepted threshold for significant change in split renal function by 10%.

The reproducibility of measurements of differential renal function in paediatric 99mTc-MAG3 renography.

OBJECTIVES: The aims of this study were to establish the reproducibility of estimates of differential renal function (DRF) obtained using the software supplied by different vendors, assess the effects of age, glomerular filtration rate (GFR) and degree of asymmetry of renal function on reproducibility and ascertain whether the software gives the same estimates of DRF. METHODS: A stratified sample of 172 renograms covering a wide range of DRF estimates, age and renal function was drawn from an electronic archive containing raw data from 1416 renograms. The renograms were processed by one operator using seven different methods, five times for each method. For each renogram and each method the DRF for the left kidney and difference between the maximum and minimum of the five estimates of DRF were calculated. RESULTS: There were differences in reproducibility among the seven methods [Friedman analysis of variance, χ(2)(N=172, d.f.=6)=367.0, P=0.0001]. Reproducibility was good with all methods in most children. The appreciable minority in whom reproducibility was not as good tended to be less than 6 months old or had GFRs below 90 ml/min/1.73 m(2) or both. The median of the DRF estimates of the left kidney obtained using the seven methods differed [Friedman analysis of variance, χ(2)(N=172, d.f.=6)=284.7, P<0.0001]. The largest difference between any two methods was 5%. CONCLUSION: Although reproducibility was good in the majority of children, an appreciable minority showed poor reproducibility, which could impact clinical decision making. It is essential that these studies be identified. This can be done by processing each renogram several times, ideally using different methods. Those with poorer reproducibility tended to be less than 6 months old or to have a low GFR.

Comparison of advanced iterative reconstruction methods for SPECT/CT.

AIM: Corrective image reconstruction methods which produce reconstructed images with improved spatial resolution and decreased noise level became recently commercially available. In this work, we tested the performance of three new software packages with reconstruction schemes recommended by the manufacturers using physical phantoms simulating realistic clinical settings. METHODS: A specially designed resolution phantom containing three (99m)Tc lines sources and the NEMA NU-2 image quality phantom were acquired on three different SPECT/CT systems (General Electrics Infinia, Philips BrightView and Siemens Symbia T6). Measurement of both phantoms was done with the trunk filled with a (99m)Tc-water solution. The projection data were reconstructed using the GE's Evolution for Bone(®), Philips Astonish(®) and Siemens Flash3D(®) software. The reconstruction parameters employed (number of iterations and subsets, the choice of post-filtering) followed theses recommendations of each vendor. These results were compared with reference reconstructions using the ordered subset expectation maximization (OSEM) reconstruction scheme. RESULTS: The best results (smallest value for resolution, highest percent contrast values) for all three packages were found for the scatter corrected data without applying any post-filtering. The advanced reconstruction methods improve the full width at half maximum (FWHM) of the line sources from 11.4 to 9.5mm (GE), from 9.1 to 6.4mm (Philips), and from 12.1 to 8.9 mm (Siemens) if no additional post filter was applied. The total image quality control index measured for a concentration ratio of 8:1 improves for GE from 147 to 189, from 179. to 325 for Philips and from 217 to 320 for Siemens using the reference method for comparison. The same trends can be observed for the 4:1 concentration ratio. The use of a post-filter reduces the background variability approximately by a factor of two, but deteriorates significantly the spatial resolution. CONCLUSIONS: Using advanced reconstruction algorithms the largest improvement in image resolution and contrast is found for the scatter corrected slices without applying post-filtering. The user has to choose whether noise reduction by post-filtering or improved image resolution fits better a particular imaging procedure.

Probable range for whole kidney mean transit time values determined by reexamination of UK audit studies.

OBJECTIVES: Inconsistency in the intercentre measurement of whole kidney mean transit time (MTT) has been reported in a previously published UK audit. The main objectives of this study were to identify a probable value of MTT for each kidney in the UK audit data and to find likely reasons for the reported variations. METHODS: Datasets of MTT values were obtained by an independent review of the audit data by four experienced practitioners of deconvolution techniques. The deconvolution techniques used included the matrix method, a constrained least squares method as well as a residence time technique. The datasets were compared using t-test, linear regression, and mean difference analysis. RESULTS: Twelve of a total of 13 datasets showed nonsignificant differences using a paired t-test (P>0.05). For each kidney (x), a collective mean and standard deviation, Mx and SDx, respectively, were calculated from these 12 datasets and a probable range was defined as Mx+/-3SDx. Average SDx/Mx was 3.6% (range 1.5-7.7%). For five kidneys, Mx exceeded the median of the audit results by 3.5-15.3 SDx (P<0.001). CONCLUSION: Probable ranges for whole kidney MTT have been estimated with good precision. Underestimation of the area under the plateau of the renal retention function as well as overestimation of the plateau height might have contributed to an underestimation of MTT apparent in some audit results. Visual display of both the renal retention function and the reconvolution curve are suggested as simple quality control measures for analysis software.

International Scientific Committee of Radionuclides in Nephrourology (ISCORN) consensus on renal transit time measurements.

This report is the conclusion of the international consensus committee on renal transit time (subcommittee of the International Scientific Committee of Radionuclides in Nephrourology) and provides recommendations on measurement, normal values, and analysis of clinical utility. Transit time is the time that a tracer remains within the kidney or within a part of the kidney (eg, parenchymal transit time). It can be obtained from a dynamic renogram and a vascular input acquired in standardized conditions by a deconvolution process. Alternatively to transit time measurement, simpler indices were proposed, such as time of maximum, normalized residual activity or renal output efficiency. Transit time has been mainly used in urinary obstruction, renal artery stenosis, or renovascular hypertension and renal transplant. Despite a large amount of published data on obstruction, only the value of normal transit is established. The value of delayed transit remains controversial, probably due to lack of a gold standard for obstruction. Transit time measurements are useful to diagnose renovascular hypertension, as are some of the simpler indices. The committee recommends further collaborative trials.

An inter-laboratory comparison study of image quality of PET scanners using the NEMA NU 2-2001 procedure for assessment of image quality.

An inter-laboratory comparison study was conducted to assess the image quality of PET scanners in Austria. The survey included both dedicated PET scanners (D-PET, n = 8) and coincidence cameras (GC-PET, n = 7). Measurement of image quality was based on the NEMA (National Electrical Manufacturers Association) NU 2-2001 protocol and the IEC (International Electrotechnical Commission) body phantom. The latter contains six fillable spheres ranging in diameter from 37 mm down to 10 mm and a 'lung' insert. The two largest lesions L1-2 simulate cold lesions, the four smaller ones (L3-6) are filled with 18F and activity concentration ratios relative to background of 8:1 and 4:1, respectively. Acquisition and reconstruction in the study employed the participating institutes' standard oncological processing protocol. Calculation of contrast of the spheres was performed with a fully automated procedure. Contrast quality indices (CQIs) reflecting global performance were obtained by summing individual contrast values. Other image quality parameters calculated according to the NEMA protocol were background variability and relative error for correction of attenuation and scatter. Contrast values obtained were 61 +/- 16 and 37 +/- 14 for L1 (per cent contrast +/- SD for D-PET and GC-PET, respectively), 57 +/- 16 and 29 +/- 16 for L2, 46 +/- 10 and 26 +/- 6.3 for L3, 37 +/- 10 and 15 +/- 4.3 for L4, 26 +/- 11.5 and 6.1 +/- 2.5 for L5, 14 +/- 7.1 and 2.6 +/- 2.6 for L6, with D-PET systems consistently being superior to GC-PET systems. CQIs permitted ranking of the scanners, also demonstrating a clear distinction between D-PET and GC-PET systems. Background variability was largest for GC-PET systems; the relative error of attenuation and scatter correction was significantly correlated with image quality for D-PET systems only. The study demonstrated considerable differences in image quality not only between GC-PET and D-PET systems but also between individual D-PET systems with possible consequences for clinical interpretation of images and measurement of quantitative indices such as the standardized uptake value. The study provided valuable feedback to the participants as well as baseline data for improving interchangeability of PET images and of quantitative indices between different laboratories.

Elimination of the influence of total renal function on renal output efficiency and normalized residual activity.

UNLABELLED: One of the potential limitations in the usefulness of both renal output efficiency (ROE) and normalized residual activity (NORA) is their residual dependence on total renal function. The purpose of this study was to present and examine a new quantitative method whereby the effects of this dependence may be removed. METHODS: The analytic method involves the determination of a retention function using an unconstrained matrix algorithm deconvolution technique followed by reconvolution with a chosen standard input function to yield a new secondary renal activity time (A/T) curve from which normalized values of ROE and NORA, denoted as N_ROE and N_NORA, respectively, can then be obtained using conventional definitions. The method has been applied in a series of 50 patient studies, which had been acquired using (99m)Tc-mercaptoacetyltriglycine (99(m)Tc-MAG3) and a standard F+18 furosemide protocol, with values of the ratio of plasma clearance to plasma volume (C/V) in the range 0.013-0.242 min(-1). RESULTS: Pre- and postnormalization values of NORA, calculated at 30 min after injection, showed a significant difference in mean values (paired t test; P < 0.001), with a maximum observed difference, DeltaNORA(30), of -4.82 (-482%) and with a SD on the paired differences, DeltaNORA(30), of 0.56 (56%) or 0.63 (63%) if background subtraction on the input function (BSIF) had been performed. In contrast, corresponding values of ROE showed a nonsignificant difference in means (P > 0.05) and a SD on the paired differences, DeltaROE(30), of 3.7% or 3.2% with and without BSIF, respectively. The normalized parameters N_ROE and N_NORA were found to be strongly linearly correlated (r = -0.99; P < 0.001), in agreement with theoretical predictions. CONCLUSION: These results suggest that renal function affects NORA significantly more than ROE. The effects can be corrected by our normalization technique, resulting in equivalent values of normalized ROE and normalized NORA.