I-123 mIBG and Tc-99m myocardial SPECT imaging to predict inducibility of ventricular arrhythmia on electrophysiology testing: a retrospective analysis.

OBJECTIVES: The purpose of this study is to assess mIBG uptake in scar border zone and its relation with ventricular arrhythmia (VA) inducibility on electrophysiology (EP) testing using I-123 mIBG SPECT and resting Tc-99m SPECT myocardial perfusion imaging (MPI). METHODS: Forty-seven patients from a previous clinical trial were retrospectively analyzed. These patients underwent I-123 mIBG and resting Tc-99m tetrofosmin SPECT, and EP testing. Twenty-eight patients were positive (EP+) and 19 patients were negative (EP-) for inducibility of sustained (>30 seconds) VA on EP testing. MPI scar extent, border zone extent, and mIBG uptake in border zone were used to predict VA inducibility on EP testing, respectively. RESULTS: There was no significant difference in scar extent between the EP+ and EP- groups. The EP+ group had significantly larger border zone and lower mIBG uptake ratio in the border zone than the EP- group. Receiver operating characteristic (ROC) curve analysis showed that the prediction accuracy for border zone extent (area under ROC = 0.75) was better than scar extent (area under ROC = 0.66). The prediction accuracy was further improved (area under ROC = 0.78), when assessing mIBG uptake in the border zone. CONCLUSION: A new tool has been developed to measure scar and border zone and to assess mIBG uptake in scar and border zone from combined I-123 MIBG SPECT and resting Tc-99m SPECT MPI. The mIBG uptake in the border zone predicted VA inducibility on EP testing with a promising accuracy.

Impact of age on myocardial uptake of ¹²³I-mIBG in older adult subjects without coronary heart disease.

BACKGROUND: The purpose of this study was to examine the relationship between myocardial uptake of (123)I-mIBG and age in older normal adult subjects. METHODS: 94 subjects (age 29-82, mean 58.5) without coronary heart disease were studied. All subjects underwent early and delayed planar and 4-hour SPECT (123)I-mIBG imaging. (123)I-mIBG uptake was quantified as heart/mediastinum ratio on planar images (H/M p) and on SPECT images (H/M s) reconstructed by filtered backprojection, ordered subsets-expectation maximization (OSEM), and OSEM with compensation for collimator septal penetration (DSP). Relationships between age and (123)I-mIBG uptake were examined by correlation analysis, t-tests, and analysis of variance. RESULTS: There was no significant correlation between age and H/M p, reflecting comparable increases in activity in the two regions of interest with age. Results on SPECT analyses were comparable, with no significant correlation between age and H/M s. Using DSP, (123)I-mIBG H/M s was significantly higher in subjects ≥70 of age compared with younger subjects. CONCLUSIONS: Both cardiac and background uptake of (123)I-mIBG increase with age in older subjects without coronary heart disease, resulting in stability of H/M results (planar and SPECT). This study suggests that prognostic analyses of quantitative (123)I-mIBG uptake in patients with heart disease do not require adjustment for patient age.

iRENEX: a clinically informed decision support system for the interpretation of 99mTc-MAG3 scans to detect renal obstruction.

PURPOSE: Decision support systems for imaging analysis and interpretation are rapidly being developed and will have an increasing impact on the practice of medicine. RENEX is a renal expert system to assist physicians evaluate suspected obstruction in patients undergoing mercaptoacetyltriglycine (MAG3) renography. RENEX uses quantitative parameters extracted from the dynamic renal scan data using QuantEM™II and heuristic rules in the form of a knowledge base gleaned from experts to determine if a kidney is obstructed; however, RENEX does not have access to and could not consider the clinical information available to diagnosticians interpreting these studies. We designed and implemented a methodology to incorporate clinical information into RENEX, implemented motion detection and evaluated this new comprehensive system (iRENEX) in a pilot group of 51 renal patients. METHODS: To reach a conclusion as to whether a kidney is obstructed, 56 new clinical rules were added to the previously reported 60 rules used to interpret quantitative MAG3 parameters. All the clinical rules were implemented after iRENEX reached a conclusion on obstruction based on the quantitative MAG3 parameters, and the evidence of obstruction was then modified by the new clinical rules. iRENEX consisted of a library to translate parameter values to certainty factors, a knowledge base with 116 heuristic interpretation rules, a forward chaining inference engine to determine obstruction and a justification engine. A clinical database was developed containing patient histories and imaging report data obtained from the hospital information system associated with the pertinent MAG3 studies. The system was fine-tuned and tested using a pilot group of 51 patients (21 men, mean age 58.2 ± 17.1 years, 100 kidneys) deemed by an expert panel to have 61 unobstructed and 39 obstructed kidneys. RESULTS: iRENEX, using only quantitative MAG3 data agreed with the expert panel in 87 % (34/39) of obstructed and 90 % (55/61) of unobstructed kidneys. iRENEX, using both quantitative and clinical data agreed with the expert panel in 95 % (37/39) of obstructed and 92 % (56/61) of unobstructed kidneys. The clinical information significantly (p < 0.001) increased iRENEX certainty in detecting obstruction over using the quantitative data alone. CONCLUSION: Our renal expert system for detecting renal obstruction has been substantially expanded to incorporate the clinical information available to physicians as well as advanced quality control features and was shown to interpret renal studies in a pilot group at a standardized expert level. These encouraging results warrant a prospective study in a large population of patients with and without renal obstruction to establish the diagnostic performance of iRENEX.

Quantitative I-123 mIBG SPECT in differentiating abnormal and normal mIBG myocardial uptake.

BACKGROUND: The purpose of this study was to evaluate global quantitation of cardiac uptake on I-123 mIBG SPECT. METHODS: The study included a pilot group of 67 subjects and a validation group of 1,051 subjects. SPECT images were reconstructed by filtered backprojection, ordered subsets expectation maximization, and deconvolution of septal penetration, respectively. SPECT heart-to-mediastinum ratio (H/M) was calculated by comparing the mean counts between heart and mediastinum volumes of interest drawn on transaxial images. Receiver operating characteristic (ROC) analysis was used to assess the capability of each SPECT method to differentiate the heart disease subjects from controls in comparison with that of the planar H/M. RESULTS: In the validation group, the areas under the ROC curves were not significantly different between the SPECT and planar H/M. Order subsets expectation maximization had significantly larger area under the ROC curve than the other two SPECT methods. CONCLUSION: H/M obtained from I-123 mIBG SPECT was equivalent to the planar H/M for differentiating between subjects with normal and abnormal mIBG uptake. Global quantification of cardiac I-123 mIBG SPECT may represent a viable alternative to the planar H/M.

Clinically viable myocardial CCTA segmentation for measuring vessel-specific myocardial blood flow from dynamic PET/CCTA hybrid fusion.

BACKGROUND: Positron emission tomography (PET)-derived LV MBF quantification is usually measured in standard anatomical vascular territories potentially averaging flow from normally perfused tissue with those from areas with abnormal flow supply. Previously we reported on an image-based tool to noninvasively measure absolute myocardial blood flow at locations just below individual epicardial vessel to help guide revascularization. The aim of this work is to determine the robustness of vessel-specific flow measurements (MBFvs) extracted from the fusion of dynamic PET (dPET) with coronary computed tomography angiography (CCTA) myocardial segmentations, using flow measured from the fusion with CCTA manual segmentation as the reference standard. METHODS: Forty-three patients' 13NH3 dPET, CCTA image datasets were used to measure the agreement of the MBFvs profiles after the fusion of dPET data with three CCTA anatomical models: (1) a manual model, (2) a fully automated segmented model and (3) a corrected model, where major inaccuracies in the automated segmentation were briefly edited. Pairwise accuracy of the normality/abnormality agreement of flow values along differently extracted vessels was determined by comparing, on a point-by-point basis, each vessel's flow to corresponding vessels' normal limits using Dice coefficients (DC) as the metric. RESULTS: Of the 43 patients CCTA fully automated mask models, 27 patients' borders required manual correction before dPET/CCTA image fusion, but this editing process was brief (2-3 min) allowing a 100% success rate of extracting MBFvs in clinically acceptable times. In total, 124 vessels were analyzed after dPET fusion with the manual and corrected CCTA mask models yielding 2225 stress and 2122 rest flow values. Forty-seven vessels were analyzed after fusion with the fully automatic masks producing 840 stress and 825 rest flow samples. All DC coefficients computed globally or by territory were ≥ 0.93. No statistical differences were found in the normal/abnormal flow classifications between manual and corrected or manual and fully automated CCTA masks. CONCLUSION: Fully automated and manually corrected myocardial CCTA segmentation provides anatomical masks in clinically acceptable times for vessel-specific myocardial blood flow measurements using dynamic PET/CCTA image fusion which are not significantly different in flow accuracy and within clinically acceptable processing times compared to fully manually segmented CCTA myocardial masks.

A software engine to justify the conclusions of an expert system for detecting renal obstruction on 99mTc-MAG3 scans.

UNLABELLED: The purposes of this study were to describe and evaluate a software engine to justify the conclusions reached by a renal expert system (RENEX) for assessing patients with suspected renal obstruction and to obtain from this evaluation new knowledge that can be incorporated into RENEX to attempt to improve diagnostic performance. METHODS: RENEX consists of 60 heuristic rules extracted from the rules used by a domain expert to generate the knowledge base and a forward-chaining inference engine to determine obstruction. The justification engine keeps track of the sequence of the rules that are instantiated to reach a conclusion. The interpreter can then request justification by clicking on the specific conclusion. The justification process then reports the English translation of all concatenated rules instantiated to reach that conclusion. The justification engine was evaluated with a prospective group of 60 patients (117 kidneys). After reviewing the standard renal mercaptoacetyltriglycine (MAG3) scans obtained before and after the administration of furosemide, a masked expert determined whether each kidney was obstructed, whether the results were equivocal, or whether the kidney was not obstructed and identified and ranked the main variables associated with each interpretation. Two parameters were then tabulated: the frequency with which the main variables associated with obstruction by the expert were also justified by RENEX and the frequency with which the justification rules provided by RENEX were deemed to be correct by the expert. Only when RENEX and the domain expert agreed on the diagnosis (87 kidneys) were the results used to test the justification. RESULTS: RENEX agreed with 91% (184/203) of the rules supplied by the expert for justifying the diagnosis. RENEX provided 103 additional rules justifying the diagnosis; the expert agreed that 102 (99%) were correct, although the rules were considered to be of secondary importance. CONCLUSION: We have described and evaluated a software engine to justify the conclusions of RENEX for detecting renal obstruction with MAG3 renal scans obtained before and after the administration of furosemide. This tool is expected to increase physician confidence in the interpretations provided by RENEX and to assist physicians and trainees in gaining a higher level of expertise.

Automated patient motion detection and correction in dynamic renal scintigraphy.

UNLABELLED: Kidney motion during dynamic renal scintigraphy can cause errors in calculated renal function parameters. Our goal was to develop and validate algorithms to detect and correct patient motion. METHODS: We retrospectively collected dynamic images from 86 clinical renal studies (42 women, 44 men), acquired using (99m)Tc-mercaptoacetyltriglycine (80 image frames [128 × 128 pixels; 3.2 mm/pixel]: twenty-four 2-s frames, sixteen 15-s frames, and forty 30-s frames). We simulated 10 types of vertical motion in each patient study, resulting in 860 image sets. Motion consisted of up or down shifts of magnitude 0.25 pixel to 4 pixels per frame and was either a gradual shift additive over multiple frames or an abrupt shift of one or more consecutive frames, with a later return to the start position. Additional horizontal motion was added to test its effect on detection of vertical motion. Original and shifted files were processed using a motion detection algorithm. Corrective shifts were applied, and the corrected and original (unshifted) images were compared pixel by pixel. Motion detected in the shifted data was also tabulated before and after correction of motion detected in the original data. A detected shift was considered correct if it was within 0.25 pixel of the simulated magnitude. Software was developed to facilitate visual review of all images and to summarize kidney motion and motion correction using linograms. RESULTS: Overall detection of simulated shifts was 99% (3,068/3,096 frames) when the existing motion in the original images was first corrected. When the original motion was not corrected, overall shift detection was 76% (2,345/3,096 frames). For image frames in which no shift was added (and original motion was not corrected), 87% (27,142/31,132 frames) were correctly detected as having no shift. When corrected images were compared with original images, calculated count recovery was 100% for all shifts that were whole-pixel magnitudes. For fractional-pixel shifts, percentage count recovery varied from 52% to 73%. Visual review suggested that some original frames exhibited true patient motion. CONCLUSION: The algorithm accurately detected motion as small as 0.25 pixel. Whole-pixel motion can be detected and corrected with high accuracy. Fractional-pixel motion can be detected and corrected, but with less accuracy. Importantly, by accurately identifying unshifted frames, the algorithm helps to prevent the introduction of errors during motion correction.