Lena Johansson

A new automated method for analysis of gated-SPECT images based on a three-dimensional heart shaped model

A new automated method for quantification of left ventricular function from gated‐single photon emission computed tomography (SPECT) images has been developed. The method for quantification of cardiac function (CAFU) is based on a heart shaped model and the active shape algorithm. The model contains statistical information of the variability of left ventricular shape. CAFU was adjusted based on the results from the analysis of five simulated gated‐SPECT studies with well defined volumes of the left ventricle. The digital phantom NURBS‐based Cardiac‐Torso (NCAT) and the Monte‐Carlo method SIMIND were used to simulate the studies. Finally CAFU was validated on ten rest studies from patients referred for routine stress/rest myocardial perfusion scintigraphy and compared with Cedar‐Sinai quantitative gated‐SPECT (QGS), a commercially available program for quantification of gated‐SPECT images. The maximal differences between the CAFU estimations and the true left ventricular volumes of the digital phantoms were 11 ml for the end‐diastolic volume (EDV), 3 ml for the end‐systolic volume (ESV) and 3% for the ejection fraction (EF). The largest differences were seen in the smallest heart. In the patient group the EDV calculated using QGS and CAFU showed good agreement for large hearts and higher CAFU values compared with QGS for the smaller hearts. In the larger hearts, ESV was much larger for QGS than for CAFU both in the phantom and patient studies. In the smallest hearts there was good agreement between QGS and CAFU. The findings of this study indicate that our new automated method for quantification of gated‐SPECT images can accurately measure left ventricular volumes and EF.

Validation of a new automated method for analysis of gated-SPECT images

We recently presented a new method for quantification of CArdiac FUnction – denoted CAFU – as the first step in the development of an automated method for integrated interpretation of gated myocardial perfusion single photon emission computed tomography (SPECT) images. The aim of this study was to validate CAFU in the assessment of global and regional function of the left ventricle. Quantitative gated‐SPECT (QGS), the most widely used software package for quantification of gated‐SPECT images, was used as reference method for the measurements of ejection fraction (EF) and ventricular volumes, and visual analysis by an experienced physician was used as reference method for the measurements of regional wall motion and thickening. Two different groups of consecutive patients referred for myocardial perfusion scintigraphy were studied. Global function was evaluated in 316 patients and regional function in 49 other patients. The studies were performed using a 2‐day stress/rest 99 m‐Tc‐sestamibi protocol. A good correlation was found between EF values from QGS and CAFU (EF CAFU = 0·84 EF QGS + 13, r = 0·94), but CAFU values were on average 4 EF points higher than QGS values. With CAFU the segments with normal thickening according to the physician showed significantly higher thickening values (in all parts of the myocardium) compared to the segments classified as having abnormal thickening. In conclusion, this study demonstrates that CAFU can be used to quantify global and regional function in gated‐SPECT images. This is an important step in our development of an automated method for integrated interpretation of gated‐SPECT myocardial perfusion scintigraphy studies.

Standardization, decay data measurements and evaluation of 64Cu.

The purposes of this study were to create national activity standards of (64)Cu, to make possible the definition of an international key comparison reference value and to determine the decay data in order to improve the decay scheme. Four laboratories measured the activity of a (64)Cu solution; these results were compared through the International Reference System. Moreover, the laboratories carried out new measurements of the photon emission intensities and of the half-life. A new decay scheme was derived from these new values and the previously published ones.

Normal limits for left ventricular ejection fraction and volumes determined by gated single photon emission computed tomography - a comparison between two quantification methods

To compare gender‐related normal limits for left ventricular (LV) ejection fraction (EF), end‐diastolic and end‐systolic volumes (EDV and ESV), obtained using two myocardial perfusion‐gated single photon emission computed tomography (SPECT) quantification methods. A total of 185 patients were retrospectively selected from a consecutive series of patients examined for coronary artery disease (CAD) or for management of known CAD. Patients were included in the study group if they had normal or probably normal results with stress and rest perfusion imaging and if the combined interpretation of perfusion studies and gated rest studies showed no signs or suspicion of myocardial infarction. The gated SPECT studies were performed using a 2‐day stress/gated rest Tc‐99m sestamibi protocol. All patient studies were processed using CAFU and quantitative‐gated SPECT (QGS), the two software packages for quantification of gated SPECT images. The lower normal limits for EF were higher for CAFU compared with QGS for both women (59% versus 53%) and men (54% versus 47%). The upper normal limits for EDV were also higher for CAFU compared with QGS for both women (133 versus 107 ml) and men (182 versus 161 ml). The differences between the software packages were small for ESV (women 44 versus 44 ml; men 69 versus 74 ml). Gender‐specific normal limits need to be applied for LV EF and volumes determined by gated SPECT. Separate criteria for abnormal LV EF and EDV need to be used for women and men depending on the software package used.

Uncertainty propagation for SPECT/CT-based renal dosimetry in (177)Lu peptide receptor radionuclide therapy.

A computer model of a patient-specific clinical (177)Lu-DOTATATE therapy dosimetry system is constructed and used for investigating the variability of renal absorbed dose and biologically effective dose (BED) estimates. As patient models, three anthropomorphic computer phantoms coupled to a pharmacokinetic model of (177)Lu-DOTATATE are used. Aspects included in the dosimetry-process model are the gamma-camera calibration via measurement of the system sensitivity, selection of imaging time points, generation of mass-density maps from CT, SPECT imaging, volume-of-interest delineation, calculation of absorbed-dose rate via a combination of local energy deposition for electrons and Monte Carlo simulations of photons, curve fitting and integration to absorbed dose and BED. By introducing variabilities in these steps the combined uncertainty in the output quantity is determined. The importance of different sources of uncertainty is assessed by observing the decrease in standard deviation when removing a particular source. The obtained absorbed dose and BED standard deviations are approximately 6% and slightly higher if considering the root mean square error. The most important sources of variability are the compensation for partial volume effects via a recovery coefficient and the gamma-camera calibration via the system sensitivity.

Decay correction of 95Nb

The (95)Nb/(95)Zr activity ratio can be used to determine the date of a nuclear event. Several proficiency test exercises organised by the National Physical Laboratory (NPL) showed in general relatively poor results for (95)Nb, presumably caused by incorrect decay corrections. In this paper, the integrated Bateman equation taking account of the multiple branching of the parents (95)Zr and (95m)Nb, ingrowth/decay during measurement and the decay correction to a specific reference time is presented.

Evaluation of a decision support system for interpretation of myocardial perfusion gated SPECT.

PurposeWe have recently presented a decision support system for interpreting myocardial perfusion scintigraphy (MPS). In this study, we wanted to evaluate the system in a separate hospital from where it was trained and to compare it with a quantification software package.MethodsA completely automated method based on neural networks was trained for the interpretation of MPS regarding myocardial ischaemia and infarction using 418 MPS from one hospital. Features from each examination describing rest and stress perfusion, regional and global function were used as inputs to different neural networks. After the training session, the system was evaluated using 532 MPS from another hospital. The test images were also processed with the quantification software package Emory Cardiac Toolbox (ECTb). The images were interpreted by experienced clinicians at both the training and the test hospital, regarding the presence or absence of myocardial ischaemia and/or infarction and these interpretations were used as gold standard.ResultsThe neural network showed a sensitivity of 90% and a specificity of 85% for myocardial ischaemia. The specificity for the ECTb was 46% (p < 0.001), measured at the same sensitivity. The neural network sensitivity for myocardial infarction was 89% and the specificity 96%. The corresponding specificity for the ECTb was 54% (p < 0.001).ConclusionA decision support system based on neural networks presents interpretations more similar to experienced clinicians compared to a conventional automated quantification software package. This study shows the feasibility of disseminating the expertise of experienced clinicians to less experienced physicians by the use of neural networks.

Validation of a new TDCR system at NPL

A new triple to double coincidence ratio (TDCR) system has been established at NPL. The system incorporates a spherical optical chamber, a manual sample changing facility and an integral light-tight housing. A 6 in diameter NaI(Tl) detector has been incorporated to allow 4pibeta-gamma coincidence measurements to be performed in parallel. Details of the detectors, the electronics and the overall TDCR system are given. Validation measurements using suitable low-energy beta and electron capture nuclides, i.e. (3)H and (55)Fe have been performed. The highest efficiency achieved with a (3)H solution in Ultima Gold AB in a glass vial was 53% and in a high-efficiency LS cocktail 65%. This indicates that the optical chamber is performing well. After varying the efficiency by de-focusing the PM tubes, the activity of the sources was determined. The activity concentration determined with TDCR agreed with certified values within the range of uncertainties. Further results from validation measurements and the corresponding uncertainty budgets are presented.

Standardisation of 89Sr using three different methods.

Three independent methods were used to standardise a 89Sr solution within the frame of an international comparison organised by BIPM/CCRI(II): 4pi liquid scintillation (LS) spectrometry, based on the CIEMAT/NIST efficiency tracing method, and direct activity measurements with a windowless 4pi CsI(Tl)-sandwich spectrometer and a 4pi pressurised gas proportional counter. Quantitative solid point-like sources were prepared paying special attention during the source drying phase. The impurities in the original solution were measured and corrected for in the results of all three methods. The activity concentration of 89Sr was found to be 26.21 +/- 0.08 kBq g(-1). A new half-life value for 89Sr of 50.61 +/- 0.05 days was determined from the LS measurements. The measurement methods, including the impurity measurements, are described and the results compared. considering the advantages and disadvantages of each method.

Standardisation of 223Ra by liquid scintillation counting techniques and comparison with secondary measurements

An aqueous solution of 223Ra chloride in equilibrium with its decay progeny was standardised by liquid scintillation counting techniques. Since secular equilibrium with the decay progeny of 223Ra had been established by the time of measurement, the apparent detection efficiency of 223Ra was approximately 6 and was determined by both the CIEMAT/NIST efficiency tracing technique and the 4π(LS)-γ digital coincidence counting techniques. The results obtained were compared with γ-spectrometry and ionisation chamber measurements. Whilst the γ-spectrometry measurements were in agreement (albeit exhibiting a large spread (18%) in the individual activity estimations using the main γ-emissions), a significant discrepancy of the order of 9% was identified between the liquid scintillation counting results and those obtained using published calibration factors for a variety of radionuclide calibrators.