Respiratory motion reduction with a dual gating approach in myocardial perfusion SPECT: Effect on left ventricular functional parameters.

BACKGROUND: Respiratory motion (RM) complicates the analysis of myocardial perfusion (MP) single-photon emission computed tomography (SPECT) images. The effects of RM on left ventricular (LV) functional variables have not been thoroughly investigated. METHODS AND RESULTS: Thoracic electrical bioimpedance and electrocardiographic signals were recorded from eighteen patients undergoing the rest phase of a 1-day stress/rest cardiac-gated MP-SPECT examination. The signals and list-mode emission data were retrospectively processed to yield standard cardiac- and dual-gated (respiratory and cardiac gating) image sets applying a novel algorithm. LV volume, MP, shape index (SI), wall motion (WM), wall thickening (WT), and phase analysis parameters were measured with Quantitative Perfusion SPECT/Quantitative Gated SPECT software (Cedars-Sinai Medical Center). Image quality was evaluated by three experienced physicians. Dual gating increased LV volume (77.1 ± 26.8 vs 79.8 ± 27.6 mL, P = .006) and decreased SI (0.57 ± 0.05 vs 0.56 ± 0.05, P = .036) and global WT (39.0 ± 11.8% vs 36.9 ± 9.4%, P = .034) compared to cardiac gating, but did not significantly alter perfusion, WM or phase analysis parameters or image quality (P > .05). CONCLUSIONS: RM reduction has an effect on LV volume, shape, and WT parameters. RM exerts no significant effect on phase analysis parameters.

Geometrical uncertainty of heart position in deep-inspiration breath-hold radiotherapy of left-sided breast cancer patients.

BACKGROUND: This study aimed to determine the geometrical uncertainty of the position of the heart with daily cone beam computed tomography (CBCT) during deep-inspiration breath-hold (DIBH) treatment of the left breast. MATERIAL AND METHODS: A visually guided optical respiratory monitoring system was used in DIBH treatment of 15 breast cancer patients. Heart position was determined in relation to the planning target volume (PTV) in 225 fractions in which daily low-dose CBCT images were compared with planning CT images. In addition, the position of the left lung apex and diaphragm was measured to evaluate the success of the DIBH. RESULTS: The median shift of the heart was 1 mm to the left, 1 mm superiorly and 0 mm in the anterior-posterior (AP) direction during the treatment course when compared to the PTV position in planning CT. Based on these movements, an AP margin of 4 mm, a lateral (LR) margin of 3 mm, and a superior-inferior (SI) margin of 5 mm should be added to the heart contour to ensure avoiding the heart when planning treatment. The distance between the left lung apex and diaphragm, applied as a surrogate for lung volume, was 2mm (median) smaller during the CBCT acquisitions than during the planning CT acquisition. The correlation coefficient between the surrogate of lung volume and the distance between the heart and PTV was r = .46 in the AP, r = .72 in the LR and r = .79 in the SI directions. CONCLUSION: Residual variation was observed in the position of the heart in comparison to PTV, even with a visually guided DIBH technique. These geometrical uncertainties should be taken into account when planning radiotherapy treatment. The success of DIBH may make a major contribution to the variation of the heart position during treatment.

Dependence of left ventricular functional parameters on image acquisition time in cardiac-gated myocardial perfusion SPECT.

BACKGROUND: Reduction of image acquisition time in single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) examinations has been considered. However, association between left ventricular (LV) functional parameters and acquisition time is unclear. METHODS: Twenty-four patients referred to one-day stress/rest SPECT MPI examinations were imaged at rest with dual-headed gamma camera. List-mode emission data were processed into sets of cardiac-gated images corresponding to different acquisition times: 20%, 30%, 40%, 50%, 60%, 80%, and 100% of total acquisition time (30 seconds per projection). Image quality was quantitatively evaluated by computing contrast-to-noise ratio. LV volumes, wall motion, wall thickening, and mechanical dyssynchrony were quantified with automatic clinical software (QGS; Cedars-Sinai Medical Center). RESULTS: A significant negative dependence was found between phase analysis parameter values and image acquisition time. Differences in LV volume parameters were small but statistically significant at relative acquisition times of less than 50%. LV wall motion and wall thickening were found to be robust to the increase of noise. CONCLUSIONS: Image acquisition time of gated SPECT MPI examination can be reduced to 15 seconds per projection without significantly affecting LV volumes, wall motion, or wall thickening. However, reduction of acquisition time has a significant effect on phase analysis results.

Comparison of end-expiratory respiratory gating methods for PET/CT.

BACKGROUND: Respiratory motion in positron emission tomography/computed tomography (PET/CT) causes underestimation of standardized uptake value (SUV) and variation of lesion volume, while PET and CT attenuation correction (CTAC) mismatch may introduce artefacts. The aim was to compare end-expiratory gating methods of PET and CTAC. MATERIAL AND METHODS: Three methods named the minimum-constant, slope-based and amplitude-median were developed and evaluated on gating efficiency. Method evaluation and optimization was performed on 23 simulated and 23 recorded signals from a mixed patient group. The optimized methods were applied in PET/CT imaging of seven patients, consisting of non-gated CTAC, whole-body PET and four-dimensional (4D) PET/CT. Gating efficiency was evaluated by preservation of the respiratory signal, PET-CTAC alignment, image noise and measurement of lesion SUV maximum (SUVmax), SUV mean (SUVmean) and volume. The methods were evaluated with non-gated PET and end-expiratory phase of five-bin phase-gated PET. End-expiratory gated 4D-CTAC and averaged CTAC were compared for attenuation correction of end-expiratory gated PET. RESULTS: Mean fraction of data preserved was larger (23-34%) with end-expiratory gating compared to phase-gated PET. End-expiratory gating showed increased SUVmax (8.2-8.4 g/ml), SUVmean (5.7-5.8 g/ml) and decreased lesion volume (-11.3-16.8%) compared to non-gated PET (SUVmax 6.2 g/ml, SUVmean 4.7 g/ml) and phase-gated PET (SUVmax 8.0 g/ml, SUVmean 5.6 g/ml). Using averaged CTAC and end-expiratory 4D-CTAC produced similar results concerning SUVmax, with less than 5% difference. Additionally, CTAC-PET-mismatch was minimal when end-expiratory 4D-CTAC was used. CONCLUSION: End-expiratory gating in PET/CT results in SUVmax and SUVmean increase and reduced lesion volume compared to non-gated PET and phase-gated PET. End-expiratory 4D-CTAC or averaged CTAC will offer similar accuracy for attenuation correction of end-expiratory gated PET.

Dosimetric effect of rotational setup errors in volumetric modulated arc therapy and field-in-field treatment of left-sided breast cancer.

Setup errors are an important factor in the dosimetric accuracy of radiotherapy delivery. In this study, we investigated how rotational setup errors influence the dose distribution in volumetric modulated arc therapy (VMAT) and tangential field-in-field (FiF) treatment of left-sided breast cancer with supraclavicular lymph node involvement in deep inspiration breath hold. Treatment planning computed tomography images and radiotherapy plans of 20 patients were collected retrospectively for the study. Rotational setup errors up to 3° were simulated by rotating the planning images, and the resulting dosimetric changes were calculated. With rotational setup errors up to 3°, the median decrease of V95% to clinical target volume was less than 0.8 percentage point in both VMAT and FiF plans. The dose distribution of the heart and left anterior descending artery was more stable with respect to rotations in VMAT plans compared to FiF plans. Correction of ≥1° setup errors is recommended due to increased doses to the heart and left anterior descending artery after 1° setup errors.

Dosimetric effect of respiratory motion on planned dose in whole-breast volumetric modulated arc therapy using moderate and ultra-hypofractionation.

BACKGROUND AND PURPOSE: The interplay effect of respiratory motion on the planned dose in free-breathing right-sided whole-breast irradiation (WBI) were studied by simulating hypofractionated VMAT treatment courses. MATERIALS AND METHODS: Ten patients with phase-triggered 4D-CT images were included in the study. VMAT plans targeting the right breast were created retrospectively with moderately hypofractionated (40.05 Gy in 15 fractions of 2.67 Gy) and ultra-hypofractionated (26 Gy 5 fractions of 5.2 Gy) schemes. 3D-CRT plans were generated as a reference. All plans were divided into respiratory phase-specific plans and calculated in the corresponding phase images. Fraction-specific dose was formed by deforming and summing the phase-specific doses in the planning image for each fraction. The fraction-specific dose distributions were deformed and superimposed onto the planning image, forming the course-specific respiratory motion perturbed dose distribution. Planned and respiratory motion perturbed doses were compared and changes due to respiratory motion and choice of fractionation were evaluated. RESULTS: The respiratory motion perturbed PTV coverage (V95%) decreased by 1.7% and the homogeneity index increased by 0.02 for VMAT techniques, compared to the planned values. Highest decrease in CTV coverage was 0.7%. The largest dose differences were located in the areas of steep dose gradients parallel to respiratory motion. The largest difference in DVH parameters between fractionation schemes was 0.4% of the prescribed dose. Clinically relevant changes to the doses of organs at risk were not observed. One patient was excluded from the analysis due to large respiratory amplitude. CONCLUSION: Respiratory motion of less than 5 mm in magnitude did not result in clinically significant changes in the planned free-breathing WBI dose. The 5 mm margins were sufficient to account for the respiratory motion in terms of CTV dose homogeneity and coverage for VMAT techniques. Steep dose gradients near the PTV edges might decrease the CTV coverage. No clinical significance was found due to the choice of fractionation.

Effect of data conserving respiratory motion compensation on left ventricular functional parameters assessed in gated myocardial perfusion SPECT.

BACKGROUND: Respiratory motion compromises image quality in myocardial perfusion (MP) single-photon emission computed tomography (SPECT) imaging and may affect analysis of left ventricular (LV) functional parameters, including phase analysis-quantified mechanical dyssynchrony parameters. In this paper, we investigate the performance of two algorithms, respiratory blur modeling (RBM) and joint motion-compensated (JMC) ordered-subsets expectation maximization (OSEM), and the effects of motion compensation on cardiac-gated MP-SPECT studies. METHODS: Image acquisitions were carried out with a dual-detector SPECT/CT system in list-mode format. A cardiac phantom was imaged as stationary and under respiratory motion. The images were reconstructed with OSEM, RBM-OSEM, and JMC-OSEM algorithms, and compared in terms of mean squared error (MSE). Subsequently, MP-SPECT data of 19 patients were binned into dual-gated (respiratory and cardiac gating) projection images. The images of the patients were analyzed with Quantitative Gated SPECT (QGS) 2012 program (Cedars-Sinai Medical Center, USA). The parameters of interest were LV volumes, ejection fraction, wall motion, wall thickening, phase analysis, and perfusion parameters. RESULTS: In phantom experiment, compared to the stationary OSEM reconstruction, the MSE values for OSEM, RBM-OSEM, and JMC-OSEM were 8.5406·10-5,2.7190·10-5, and 2.0795·10-5, respectively. In the analysis of LV function, use of JMC had a small but statistically significant (p < 0.05) effect on several parameters: it increased LV volumes and standard deviation of phase angle histogram, and it decreased ejection fraction, global wall motion, and lateral, septal, and apical perfusion. CONCLUSIONS: Compared to standard OSEM algorithm, RBM-OSEM and JMC-OSEM both improve image quality under motion. Motion compensation has a minor effect on LV functional parameters.

Time-modified OSEM algorithm for more robust assessment of left ventricular dyssynchrony with phase analysis in ECG-gated myocardial perfusion SPECT.

BACKGROUND: In ordered subsets expectation maximization (OSEM) reconstruction of electrocardiography (ECG)-gated myocardial perfusion single-photon emission computed tomography (SPECT), it is often assumed that the image acquisition time is constant for each projection angle and ECG bin. Due to heart rate variability (HRV), this assumption may lead to errors in quantification of left ventricular mechanical dyssynchrony with phase analysis. We hypothesize that a time-modified OSEM (TOSEM) algorithm provides more robust results. METHODS: List-mode data of 44 patients were acquired with a dual-detector SPECT/CT system and binned to eight ECG bins. First, activity ratio (AR)-the ratio of total activity in the last OSEM-reconstructed ECG bin and first five ECG bins-was computed, as well as standard deviation SDR-R of the accepted R-R intervals; their association was evaluated with Pearson correlation analysis. Subsequently, patients whose AR was higher than 90% were selected, and their list-mode data were rebinned by omitting a part of the acquired counts to yield AR values of 90%, 80%, 70%, 60% and 50%. These data sets were reconstructed with OSEM and TOSEM algorithms, and phase analysis was performed. Reliability of both algorithms was assessed by computing concordance correlation coefficients (CCCs) between the 90% data and data corresponding to lower AR values. Finally, phase analysis results assessed from OSEM- and TOSEM-reconstructed images were compared. RESULTS: A strong negative correlation (r = -0.749) was found between SDR-R and AR. As AR decreased, phase analysis parameters obtained from OSEM images decreased significantly. On the contrary, reduction of AR had no significant effect on phase analysis parameters obtained from TOSEM images (CCC > 0.88). The magnitude of difference between OSEM and TOSEM results increased as AR decreased. CONCLUSIONS: TOSEM algorithm minimizes the HRV-related error and can be used to provide more robust phase analysis results.

Effect of respiratory motion on cardiac defect contrast in myocardial perfusion SPECT: a physical phantom study.

OBJECTIVE: Correction for respiratory motion in myocardial perfusion imaging requires sorting of emission data into respiratory windows where the intra-window motion is assumed to be negligible. However, it is unclear how much intra-window motion is acceptable. The aim of this study was to determine an optimal value of intra-window residual motion. METHODS: A custom-designed cardiac phantom was created and imaged with a standard dual-detector SPECT/CT system using Tc-99m as the radionuclide. Projection images were generated from the list-mode data simulating respiratory motion blur of several magnitudes from 0 (stationary phantom) to 20 mm. Cardiac defect contrasts in six anatomically different locations, as well as myocardial perfusion of apex, anterior, inferior, septal and lateral walls, were measured at each motion magnitude. Stationary phantom data were compared to motion-blurred data. Two physicians viewed the images and evaluated differences in cardiac defect visibility and myocardial perfusion. RESULTS: Significant associations were observed between myocardial perfusion in the anterior and inferior walls and respiratory motion. Defect contrasts were found to decline as a function of motion, but the magnitude of the decline depended on the location and shape of the defect. Defects located near the cardiac apex lost contrast more rapidly than those located on the anterior, inferior, septal and lateral wall. The contrast decreased by less than 5% at every location when the motion magnitude was 2 mm or less. According to a visual evaluation, there were differences in myocardial perfusion if the magnitude of the motion was greater than 1 mm, and there were differences in the visibility of the cardiac defect if the magnitude of the motion was greater than 9 mm. CONCLUSIONS: Intra-window respiratory motion should be limited to 2 mm to effectively correct for respiratory motion blur in myocardial perfusion SPECT.

Dosimetric evaluation of modern radiation therapy techniques for left breast in deep-inspiration breath-hold.

PURPOSE: The dosimetric differences between four radiation therapy techniques for left sided whole breast irradiation were evaluated side by side in the same patient population. METHODS: Radiotherapy treatment plans were retrospectively created with Accuray TomoDirect (TD), Elekta Volumetric Modulated Arc Therapy (E-VMAT), Varian RapidArc (RA) and Field-in-field (FinF) technique for 20 patients, who had received left breast irradiation during deep-inspiration breath-hold. Dose characteristics of planning target volume and organs at risk were compared. RESULTS: The E-VMAT, TD and RA treatment plans had higher target coverage (V95%) than FinF plans (97.7-98.3% vs. 96.6%). The low-dose spillage to contralateral breast and lung was smaller with FinF and TD (mean 0.1 and 0.3 Gy) compared to E-VMAT and RA (mean 0.6 and 0.9 Gy). E-VMAT, RA and TD techniques were more effective than FinF in sparing left anterior descending artery (mean 4.0, 4.2 and 4.7 Gy vs. 6.1 Gy, respectively). CONCLUSIONS: In whole breast irradiation TD, E-VMAT and RA plans generated in this study achieved higher dose coverage and sparing of organs from the high dose in the vicinity of the PTV. The advantage of calculated FinF plans is the lowest dose on contralateral organs. The choice of the technique used should be weighted by each institution taking into account the dose characteristics of each technique and its fit with patient anatomy bearing in mind the increased workload of using modulated techniques and the increased beam on time.

Flattening filter free technique in breath-hold treatments of left-sided breast cancer: The effect on beam-on time and dose distributions.

BACKGROUND AND PURPOSE: The use of flattening filter free (FFF) beams has potential to speed up deep-inspiration breath-hold treatments. In this study, the beam-on time and dose characteristics of left-sided breast treatment plans with FFF and flattened beams were evaluated. MATERIAL AND METHODS: Twelve plans were generated for 20 patients. The techniques utilized were volumetric modulated arc therapy with two limited tangential arcs (tVMAT) and tangential intensity modulated radiotherapy with dynamic (dIMRT) as well as step-and-shoot (FinF) dose delivery. Each technique was planned with FFF and flattened beams with 6 and 10MV photons. All plans were irradiated and the beam-on times were measured. Dose characteristics of planning target volume (PTV) and organs at risk (OAR) were evaluated. RESULTS: The mean beam-on times were reduced by 18-39% using FFF. Mean PTV dose coverage was least reduced with tVMAT (0.6-0.8%) compared to dIMRT (4%) and FinF (5.6-9.1%), when FFF beams were used instead of flattened beams. Only small differences were observed in OAR doses between equivalent plans (FFF vs. flattened). CONCLUSIONS: A significant reduction was observed in beam-on time when utilizing FFF beams with tVMAT, dIMRT and FinF. tVMAT was the only technique for which the use of FFF did not degrade the treatment plan dose distributions.

BMI influence on the reproducibility of ECG-gated myocardial perfusion imaging phase analysis in comparison with novel echocardiographic dyssynchrony estimation methods.

AIM: Cardiac resynchronization therapy (CRT) is a treatment for patients with end-stage heart failure. However, two-thirds of the patients are nonresponders. Evaluation of left ventricular mechanical dyssynchrony may help in finding patients who will benefit from CRT. Dyssynchrony can be evaluated by the phase analysis method in myocardial perfusion imaging (MPI) or with cardiac ultrasound. The aim of this study was to investigate the reproducibility of phase analysis parameters in MPI and echocardiographic parameters in the evaluation of left ventricular mechanical dyssynchrony. In particular, the influence of BMI on reproducibility was studied. METHODS AND RESULTS: Twenty-one patients underwent an ECG-gated MPI scan. Acquisition was repeated after the rest image. The patients were also studied twice with transthoracic echocardiography. Of MPI phase analysis parameters bandwidth, histogram SD and entropy% were highly reproducible in the pooled population: Cronbach's α 0.927-0.967 and intraclass correlation (ICC) 0.868-0.967, (P<0.001 for all). However, the reproducibility of bandwidth and SD was poorer in patients with BMI≥29 kg/m group (α 0.203 and -0.055; ICC 0.106 and -0.027, NS for both) than in those with BMI<29 kg/m (α 0.984 and 0.980; ICC 0.968 and 0.961, P<0.001 for both). In contrast, BMI had no obvious influence on the reproducibility of global longitudinal strain in echocardiography. CONCLUSION: Parameters reflecting mechanical dyssynchrony were found to be well reproducible. However, this study indicates that phase analysis results may be less reproducible in patients with high BMI, whereas global longitudinal strain in echocardiography seems to be less critical for a patient's BMI.

A novel respiratory gating method for oncologic positron emission tomography based on bioimpedance approach.

OBJECTIVE: Respiratory motion causes loss of image quality and inaccuracy of quantification in oncologic positron emission tomography (PET) imaging. This study introduces a bioimpedance-based gating method for compensation of respiratory motion artefacts. METHODS: The bioimpedance-based respiratory gating method was studied parallel to a clinically used respiratory gating method [Real-time Position Management by Varian Medical Systems] in 4D PET/CT acquisition of 9 oncologic patients. The quantitative analysis consisted of the evaluation of tumour SUVpeak, SUVmax and volume. Additionally, target-to-background ratios as well as motion in cranial-caudal and anterior-posterior directions were measured. The evaluation was performed with amplitude- and time-based gating using averaged attenuation correction maps. RESULTS: Bioimpedance gating resulted in 17.7-18.9 % increase in mean SUVpeak and 20.0-21.4 % decrease in mean volume compared to non-gated images. The maximum motion measured from the bioimpedance-gated images was 19 mm in cranial-caudal direction and 9 mm in anterior-posterior direction. CONCLUSIONS: Bioimpedance-based respiratory gating compensates the adverse effects of motion in oncologic PET imaging.

An integrated bioimpedance--ECG gating technique for respiratory and cardiac motion compensation in cardiac PET.

Respiratory motion may degrade image quality in cardiac PET imaging. Since cardiac PET studies often involve cardiac gating by ECG, a separate respiratory monitoring system is required increasing the logistic complexity of the examination, in case respiratory gating is also needed. Thus, we investigated the simultaneous acquisition of both respiratory and cardiac gating signals using II limb lead mimicking electrode configuration during cardiac PET scans of 11 patients. In addition to conventional static and ECG-gated images, bioimpedance technique was utilized to generate respiratory- and dual-gated images. The ability of the bioimpedance technique to monitor intrathoracic respiratory motion was assessed estimating cardiac displacement between end-inspiration and -expiration. The relevance of dual gating was evaluated in left ventricular volume and myocardial wall thickness measurements. An average 7.6 ± 3.3 mm respiratory motion was observed in the study population. Dual gating showed a small but significant increase (4 ml, p = 0.042) in left ventricular myocardial volume compared to plain cardiac gating. In addition, a thinner myocardial wall was observed in dual-gated images (9.3 ± 1.3 mm) compared to cardiac-gated images (11.3 ± 1.3 mm, p = 0.003). This study shows the feasibility of bioimpedance measurements for dual gating in a clinical setting. The method enables simultaneous acquisition of respiratory and cardiac gating signals using a single device with standard ECG electrodes.

Optimizing bioimpedance measurement configuration for dual-gated nuclear medicine imaging: a sensitivity study.

Motion artefacts due to respiration and cardiac contractions may deteriorate the quality of nuclear medicine imaging leading to incorrect diagnosis and inadequate treatment. Motion artefacts can be minimized by simultaneous respiratory and cardiac gating, dual-gating. Currently, only cardiac gating is often performed. In this study, an optimized bioimpedance measurement configuration was determined for simultaneous respiratory and cardiac gating signal acquisition. The optimized configuration was located on anterolateral upper thorax based on sensitivity simulations utilizing a simplified thorax model. The validity of the optimized configuration was studied with six healthy volunteers. In the peak-to-peak and frequency content analyses the optimized configuration showed consistently higher peak-to-peak values and frequency content than other studied measurement configurations. This study indicates that the bioimpedance method has potential for the dual-gating in nuclear medicine imaging. The method would minimize the need of additional equipment, is easy for the technologists to use and comfortable for the patients.