Electrocardiographically gated thin-section CT of the lung.

PURPOSE: To determine whether electrocardiographic (ECG) gating improves image quality of thin-section computed tomographic (CT) scans of the lung obtained with a subsecond CT scanner. MATERIALS AND METHODS: Thin-section CT was performed in 35 patients by using standard techniques. Three additional sections were obtained in each patient with prospective ECG gating at corresponding levels of the paracardiac lung parenchyma. Non-ECG-gated and ECG-gated sections were then rated in blinded fashion by three experienced radiologists for overall image quality, spatial resolution, and diagnostic value and for different types of respiratory and cardiac motion artifacts. RESULTS: ECG gating helped significantly reduce artifacts caused by cardiac motion (i.e., distortion of pulmonary vessels, double images, or blurring of the cardiac border) (P < .05). ECG gating did not reduce respiratory motion artifacts. In patients with heart rates of less than 76 beats per minute, ECG gating significantly improved overall image quality (P = .041). ECG gating was not perceived to increase the diagnostic value of thin-section CT scans. CONCLUSION: ECG gating improves image quality of thin-section CT scans of the lung by reducing cardiac motion artifacts that may mimic disease. It must be established whether ECG gating can help increase the diagnostic accuracy of thin-section CT for the evaluation of subtle parenchymal disease.     

External radioactive markers for PET data-driven respiratory gating in positron emission tomography

Purpose

Respiratory gating is an established approach to overcoming respiration-induced image artefacts in PET. Of special interest in this respect are raw PET data-driven gating methods which do not require additional hardware to acquire respiratory signals during the scan. However, these methods rely heavily on the quality of the acquired PET data (statistical properties, data contrast, etc.). We therefore combined external radioactive markers with data-driven respiratory gating in PET/CT. The feasibility and accuracy of this approach was studied for [¹⁸F]FDG PET/CT imaging in patients with malignant liver and lung lesions.

Methods

PET data from 30 patients with abdominal or thoracic [¹⁸F]FDG-positive lesions (primary tumours or metastases) were included in this prospective study. The patients underwent a 10-min list-mode PET scan with a single bed position following a standard clinical whole-body [¹⁸F]FDG PET/CT scan. During this scan, one to three radioactive point sources (either ²²Na or ¹⁸F, 50–100 kBq) in a dedicated holder were attached the patient’s abdomen. The list mode data acquired were retrospectively analysed for respiratory signals using established data-driven gating approaches and additionally by tracking the motion of the point sources in sinogram space. Gated reconstructions were examined qualitatively, in terms of the amount of respiratory displacement and in respect of changes in local image intensity in the gated images.

Results

The presence of the external markers did not affect whole-body PET/CT image quality. Tracking of the markers led to characteristic respiratory curves in all patients. Applying these curves for gated reconstructions resulted in images in which motion was well resolved. Quantitatively, the performance of the external marker-based approach was similar to that of the best intrinsic data-driven methods. Overall, the gain in measured tumour uptake from the nongated to the gated images indicating successful removal of respiratory motion was correlated with the magnitude of the respiratory displacement of the respective tumour lesion, but not with lesion size.

Conclusion

Respiratory information can be assessed from list-mode PET/CT through PET data-derived tracking of external radioactive markers. This information can be successfully applied to respiratory gating to reduce motion-related image blurring. In contrast to other previously described PET data-driven approaches, the external marker approach is independent of tumour uptake and thereby applicable even in patients with poor uptake and small tumours.     

呼吸门控PET/CT对肺部结节SUV的影响

目的 观察呼吸门控与非门控PET/CT显像测定肺部结节SUV的差异,探讨不同呼吸时相SUV变化趋势.方法 2010年5月至2011年3月进行PET/CT显像、发现有多个肺部结节并同意进行呼吸门控显像者共19例,最终14例共37个结节纳入该研究,其中男6例,女8例,年龄29 ～ 80(63.7±7.1)岁.对所有患者进行常规和呼吸门控PET/CT采集.经过后台处理得到呼吸时相相匹配的1个呼吸周期内6个时相的PET/CT融合图像.测得SUV,每个肺部结节的每个指标均进行非门控与门控显像6个时相共7次测量.采用SPSS 13.0软件对数据行t检验、秩和检验和相关分析.结果 37个肺部结节呼吸门控显像的SUVmax和SUVmean分别为13.69±6.70和8.56±4.11,明显高于非门控PET/CT的12.76±6.74及7.66±4.00(t =3.475和Z=-3.661,P均＜0.001);但2种显像技术SUVmax与SUVmean相关性好(r=0.971和0.969,P均＜0.05);在门控显像中,6个时相不同时相间SUV以时相1即吸气末最高,而时相4(呼气末吸气初)最低.37个结节中4个结节常规显像SUV＜ 2.5(定义为轻度摄取),其中有1个结节SUVmax由非门控显像的2.13升至门控显像的2.52.结论 采用呼吸门控PET/CT显像所得到的肺部结节SUVmax和SUVmean比非门控常规采集高,但两者相关性好;SUV不同时相间以吸气末最高.对轻度摄取FDG的结节,经呼吸门控PET/CT其SUV有所提高,有可能影响临床诊断.     

Retrospective motion gating in small animal CT of mice and rats

OBJECTIVES: Implementation and evaluation of retrospective respiratory and cardiac gating of mice and rats using a flat-panel volume-CT prototype (fpVCT). MATERIALS AND METHODS: Respiratory and cardiac gating was implemented by equipping a fpVCT with a small animal monitoring unit. ECG and breathing excursions were recorded and 2 binary gating signals derived. Mice and rats were scanned continuously over 80 seconds after administration of blood-pool contrast media. Projections were chosen to reconstruct volumes that fall within defined phases of the cardiac/respiratory cycle. RESULTS: Multireader analysis indicated that in gated still images motion artifacts were strongly reduced and diaphragm, tracheobronchial tract, heart, and vessels sharply delineated. From 4D series, functional data such as respiratory tidal volume and cardiac ejection fraction were calculated and matched well with values known from literature. DISCUSSION: Implementation of retrospective gating in fpVCT improves image quality and opens new perspectives for functional cardiac and lung imaging in small animals.     

Respiratory gating in magnetic resonance imaging: improved image quality over non-gated images for equal scan time

Magnetic resonance image quality is adversely affected by respiratory (RESP) motion during the scan. Respiratory gating improves magnetic resonance image (MRI) quality and removes artifacts, but has not been widely used, as RESP gating increases scan time. Our RESP-gating device was used to study scan time versus improvement in image quality using various gating modes; with and without combined electrocardiographic (ECG) gating. When RESP scans were acquired for the same time as non-gated scans, by using a wide RESP-gating window bracketing end expiration and a reduced number of pulse sequence repetitions, substantial improvement in image quality (over non-gated scans) resulted, despite the inferior statistical content of the acquisition.     

Free-breathing three-dimensional computed tomography of the lung using prospective respiratory gating: charge-coupled device camera and laser sensor device in an animal experiment

PURPOSE: The aim was to investigate the feasibility and image quality of prospective respiratory gating for 3-D computed tomography (CT) of the lung. MATERIAL AND METHODS: Eight anesthetized pigs underwent prospectively gated multidetector computed tomography using 2 devices: a charge-coupled device (CCD) camera and a laser sensor. The output signal of both gating devices was connected to the scanner instead of ECG unit. Inspiratory and expiratory images were obtained during "free-breathing" and analyzed in MPR mode for sharpness of bronchi, diaphragm and lung using a 4-point-score (1, excellent to 4, severe artifacts). RESULTS: The CCD camera worked in all animals. Using the laser sensor, only 50% of expiratory scans could be acquired. All acquired images showed excellent sharpness (CCD camera vs. laser sensor) for trachea (1.1 +/- 0.3 vs. 1.3 +/- 0.5), bronchi (1.4 +/- 0.7 vs. 1.8 +/- 0.6), lung fissures (1.0 vs. 1.1 +/- 0.3), and lung parenchyma (1.0 +/- 0.2 vs. 1.4 +/- 0.6), and minor to major artifacts for diaphragm (1.5 +/- 0.8 vs. 2.0 +/- 1.0, P < 0.05) and pericardial lung structures (1.9 +/- 0.7 vs. 2.3 +/- 0.5). CONCLUSION: High image quality for inspiratory and expiratory scans was achieved by free-breathing 3-D CT of the lung using noncontact prospective respiratory gating.     

Comparison of gated and non-gated fast multislice black-blood carotid imaging using rapid extended coverage and inflow/outflow saturation techniques

PURPOSE: To comparatively analyze two fast in vivo multislice black-blood carotid artery vessel wall imaging techniques with and without cardiac gating. MATERIALS AND METHODS: Eight subjects with carotid artery atherosclerosis, and four healthy subjects were studied using two black-blood multislice techniques: rapid extended coverage double inversion recovery (REX-DIR), and inflow/outflow saturation band (IOSB) rapid acquisition with relaxation enhancement (RARE) multislice acquisitions. Quantitative, qualitative, and morphometric analyses were performed on images. RESULTS: Gating produced significantly lower values for the REX-DIR sequence with respect to signal intensity in muscle and the carotid artery wall, whereas it had no effect on flow suppression compared to non-gated images. For the IOSB sequences, gating had no significant effect on signal intensity of muscle and the carotid artery wall, but worsened flow suppression. REX-DIR and IOSB sequences were statistically different with respect to signal intensity of muscle (with REX-DIR sequences having lower values), while no statistical significance was observed for flow suppression and wall delineation. A morphologic analysis of the vessel wall and lumen comparing REX-DIR gated, IOSB gated, REX-DIR non-gated, and IOSB non-gated sequences revealed no significant differences between the acquisition techniques tested. CONCLUSION: Non-gated sequences may be used instead of gated sequences in atherosclerotic vessel wall imaging without compromising image quality. This may shorten examination time and improve patient comfort.     

Is the addition of ECG gating to technetium-99m sestamibi SPET of value in the assessment of myocardial viability?

The main goal of this study was to evaluate whether the addition of ECG gating to technetium-99m sestamibi single-photon emission tomography (SPET) perfusion imaging assists the prediction of recovery of regional wall motion abnormalities after revascularization. Thirty-six patients with coronary artery disease were included in the study. All had wall motion abnormalities, and 31 (86%) had a clinical history of myocardial infarction. Coronary artery bypass surgery was performed in 18 patients and angioplasty in the remainder. All underwent ECG-gated and non-gated SPET at rest and after intravenous dipyridamole. Two-dimensional echocardiography was performed at a mean of 27 days before revascularization and at a mean of 69 days following revascularization to assess segmental wall motion changes. Perfusion prior to revascularization was analysed qualitatively and quantitatively on gated and non-gated SPET, and the results compared with those of echocardiography. Bullseye parameters were obtained from a normal database, generated from data in 40 normal volunteers, using dipyridamole ECG-gated and non-gated sestamibi SPET. There was good concordance between gated and non-gated qualitative analysis (79% with kappa=0.65) for normal, viable or necrotic segments. Gated SPET predicted functional recovery in 27 of 35 (77%) segments showing echocardiographic improvement while non-gated SPET did so in 30 of 39 (77%) such segments. Gated SPET predicted no functional recovery in 20 of 45 (44%) segments that did not show improved wall motion after revascularization, while with non-gated SPET the figure was 18 of 51 (35%). The positive predictive values of gated and non-gated SPET with regard to the recovery of wall motion following revascularization were 52% and 48%, while the negative predictive values were 71% and 67%, respectively.^99mTc-sestamibi had a low predictive value for recovery of function if visual assessment was used in the analysis of SPET data. Quantitative bullseye sestamibi parameters (defect extension and severity, reversibility and percentage change in extension), from gated or non-gated studies, appear best to distinguish which segments will display improved motility on the echocardiogram after revascularization. The addition of ECG gating does not significantly increase the predictive value of SPET imaging with regard to recovery of function.     

Pulmonary perfusion assessment with respiratory gated 99mTc macroaggregated albumin SPECT: preliminary results

PURPOSE: Respiratory gated perfusion single photon emission computed tomography (SPECT) was applied to reduce respiratory lung motion effects and to reliably assess perfusion impairment in various lung diseases. METHODS: After injection of 259 MBq of 99mTc macroaggretated albumin (99mTc-MAA), gating was performed using a triple-headed SPECT unit connected to a physiological synchronizer in a total of 35 patients with either obstructive lung diseases (n = 14), pulmonary embolism (n = 8), small lung nodules (n = 7) or acute interstitial pneumonia (n = 6). Projection data were acquired in a 64 x 64 matrix, with 20 stops over 120 degrees for each detector with a preset time of 15 s for each stop. Inadequate data for the respiratory cycle were automatically eliminated. In addition to end inspiration images and end expiration images derived from 12.5% threshold data centred at peak inspiration and expiration for each respiratory cycle, respectively, an ungated image was obtained from full respiratory cycle data. RESULTS: Gated images were completed for 13.7 +/- 1.8 min in all subjects. Although the total lung radioactivity of the gated images were reduced to approximately 13% of that of the ungated images, these gated images showed uniform perfusion in the unaffected lungs and visualized a total of 94 (21.9%) additional perfusion defects against 429 defects visualized on ungated images in 31 patients with focal perfusion defects. Among the perfusion defects visualized on both gated images, the defect size was occasionally larger on the end inspiration images. The end expiration images showed significantly higher lesion-to-normal lung radioactivity ratios compared with those on the end expiration and ungated images in the affected lower lungs throughout the lung diseases. Radioactivity changes per pixel between end inspiration and end expiration images in the affected lower lungs of the obstructive lung diseases were significantly lower compared with those of pulmonary embolism and acute interstitial pneumonia (P<0.0001 and P<0.01, respectively). CONCLUSION: This technique appears to enhance the clarity of perfusion defects, and lung radioactivity changes between end inspiration and end expiration may characterize regionally impaired ventilation status.     

Retrospective gating for mouse cardiac MRI.

Cardiac MR imaging in small animals presents some difficulties due to shorter cardiac cycles and smaller dimensions than in human beings, but prospectively gated techniques have been successfully applied. As with human imaging, there may be certain applications in animal imaging for which retrospective gating is preferable to prospective gating. For example, cardiac imaging in multiple mice simultaneously is one such application. In this work we investigate the use of retrospective gating for cardiac imaging in a mouse. Using a three-dimensional imaging protocol, we show that image quality with retrospective gating is comparable to prospectively gated imaging. We conclude that retrospective gating is applicable for small animal cardiac MRI and show how it can be applied to the problem of cardiac MRI in multiple mice.     

Movement of a small tumour in contact with the diaphragm: characterisation with four-dimensional CT

Radiotherapy to the thoracic and abdominal regions can require tailoring of the planning target volume (PTV) to compensate for respiratory motion. We evaluated dose variations that might occur to a small target close to the diaphragm. We compared tumour and diaphragm displacement in gated and non-gated four-dimensional computed tomography (CT) of a patient with a peridiaphragmatic lesion, using peak exhalation as a baseline. Diaphragmatic motion was 12.7 mm in the inferior direction. The tumour was noted to move 1.0 mm to the right, 1.1 mm anteriorly, and 1.4 mm superiorly. The tumour moved in the opposite direction from the diaphragm in the vertical axis. This paradoxical motion did not affect the dose distribution because the beam did not irradiate the liver on non-gated treatment plans, and remained within the PTV. We observed minimal movement of a small tumour on 4D CT, in spite of it being in contact with, and moving opposite to, the diaphragm. In this patient, respiratory gating during irradiation was not needed, making it possible to reduce the treatment time.     

Dynamic computed tomography of the neonatal lung: volume calculations and validation in an animal model

PURPOSE: The purpose of this study was to evaluate and validate dynamic volume calculation by respiratory-gated multislice computed tomography (CT) in small neonatal animals. MATERIALS AND METHODS: Six mechanically ventilated newborn piglets were imaged in a multislice CT with 0.5-mm slice thickness (4:16 pitch, 0.5-second rotation time, 120 kV). The respirator was connected to the CT unit for recording the respiratory signal. Simultaneously, tidal volume was measured by the respirator and functional residual capacity (FRC) using a multiple-breath washin-washout technique (MBW) with heptafluoropropane (HFP) as tracer gas. Complete volume datasets were reconstructed throughout the respiratory cycle in increments of 10% using retrospective half-scan gating. All animals were scanned in 3 different ventilator settings. Dynamic lung volumes (tidal volumes) were calculated by means of segmentation of the lung parenchyma during the respiratory cycle using work-in-progress software. RESULTS: The mean (+/-standard deviation) FRC determined by CT was 24.7+/-8.6 mL versus 24.8+/-7.3 mL for the MBW technique. There was no statistically significant difference (P=0.555). Pearson's correlation coefficient showed a strong correlation between the data obtained with CT and that obtained with the MBW technique (r=0.886). After exclusion of one outlier, tidal volumes showed a similar correlation (r=0.837) without significant differences in the mean values (CT: 8.9+/-2.4 mL and respirator: 8.7+/-2.4 mL, P=0.566). CONCLUSION: Dynamic multislice CT with respiratory gating allows for calculation of lung volumes and may be useful for future CT applications in human neonatal lung imaging.     

Respiratory bellows revisited for motion compensation: Preliminary experience for cardiovascular MR

For many cardiac MR applications, respiratory bellows gating is attractive because it is widely available and not disruptive to or dependent on imaging. However, its use is uncommon in cardiac MR, because its accuracy has not been fully studied. Here, in 10 healthy subjects, the bellows and respiratory navigator (NAV) with the displacement of the diaphragm and heart were simultaneously monitored, during single‐shot imaging. Furthermore, bellows‐gated and NAV‐gated coronary MRI were compared using a retrospective reconstruction at identical efficiency. There was a strong linear relationship for both the NAV and the abdominal bellows with the diaphragm (R = 0.90 ± 0.05 bellows, R = 0.98 ± 0.01 NAV, P < 0.001) and the heart (R = 0.89 ± 0.06 bellows, R = 0.96 ± 0.02 NAV, P = 0.004); thoracic bellows correlated less strongly. The image quality of bellows‐gated coronary MRI was similar to NAV‐gated and superior to no‐gating (P < 0.01). In conclusion, bellows provides a respiratory monitor which is highly correlated with the NAV and suitable for respiratory compensation in selected cardiac MR applications. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Amplitude-based optimal respiratory gating in positron emission tomography in patients with primary lung cancer

Objectives

Respiratory motion during PET imaging introduces quantitative and diagnostic inaccuracies, which may result in non-optimal patient management. This study investigated the effects of respiratory gating on image quantification using an amplitude-based optimal respiratory gating (ORG) algorithm.

Methods

Whole body FDG-PET/CT was performed in 66 lung cancer patients. The respiratory signal was obtained using a pressure sensor integrated in an elastic belt placed around the patient’s thorax. ORG images were reconstructed with 50 %, 35 %, and 20 % of acquired PET data (duty cycle). Lesions were grouped into anatomical locations. Differences in lesion volume between ORG and non-gated images, and mean FDG-uptake (SUV_mean) were calculated.

Results

Lesions in the middle and lower lobes demonstrated a significant SUV_mean increase for all duty cycles and volume decrease for duty cycles of 35 % and 20 %. Significant increase in SUV_mean and decrease in volume for lesions in the upper lobes were observed for a 20 % duty cycle. The SUV_mean increase for central lesions was significant for all duty cycles, whereas a significant volume decrease was observed for a duty cycle of 20 %.

Conclusions

This study implies that ORG could influence clinical PET imaging with respect to response monitoring and radiotherapy planning.

Key Points

? Quantifying lesion volume and uptake in PET is important for patient management ? Respiratory motion artefacts introduce inaccuracies in quantification of PET images ? Amplitude-based optimal respiratory gating maintains image quality through selection of duty cycle ? The effect of respiratory gating on lesion quantification depends on anatomical location     

The motivations and methodology for high-throughput PET imaging of small animals in cancer research

Over the last decade, small-animal PET imaging has become a vital platform technology in cancer research. With the development of molecularly targeted therapies and drug combinations requiring evaluation of different schedules, the number of animals to be imaged within a PET experiment has increased. This paper describes experimental design requirements to reach statistical significance, based on the expected change in tracer uptake in treated animals as compared to the control group, the number of groups that will be imaged, and the expected intra-animal variability for a given tracer. We also review how high-throughput studies can be performed in dedicated small-animal PET, high-resolution clinical PET systems and planar positron imaging systems by imaging more than one animal simultaneously. Customized beds designed to image more than one animal in large-bore small-animal PET scanners are described. Physics issues related to the presence of several rodents within the field of view (i.e. deterioration of spatial resolution and sensitivity as the radial and the axial offsets increase, respectively, as well as a larger effect of attenuation and the number of scatter events), which can be assessed by using the NEMA NU?4 image quality phantom, are detailed.     

呼吸运动伪影的校正及其与肺部SUV的关系

ET/CT在疾病诊断和疗效评价上起着重要作用, 但是呼吸运动伪影给病变的诊断及治疗带来困扰, 临床有多种方法可以用来对呼吸运动伪影进行校正, 其中应用最广泛的是呼吸门控技术。其对呼吸运动伪影校正后可以明显提高肺部病变的最大标准化摄取值, 从而提高图像质量及诊断的准确性。     

Initial application of respiratory-gated 201Tl SPECT in pulmonary malignant tumours

AIM: Respiratory-gated thallium-201 chloride (201Tl) single photon emission computed tomography (SPECT) was used in preliminary investigations to reduce the adverse respiratory motion effects observed on standard ungated SPECT images and to obtain reliable fusion images with computed tomography (CT) in patients with malignant lung tumours. METHODS: Fifteen patients with primary lung cancer (n=10) or metastatic lung tumours (n=5) underwent gated SPECT 20 min after intravenous injection of 148 MBq 201Tl, using triple-headed SPECT and laser light respiratory tracking units. Projection data were acquired by a step and shoot mode, with 20 stops over 120 degrees for each detector and a preset time of 30 s for each 6 degrees stop. Gated end-inspiratory and ungated images were obtained from 1/8 data centred at peak inspiration for each regular respiratory cycle and for the full respiratory cycle data, respectively. The degree and size of tumour 201Tl uptake were compared between these images by regions of interest (ROI) analysis. Gated SPECT images were registered with rest inspiratory CT images using an automated three-dimensional (3D) image registration tool. Registration mismatch was assessed by measuring the 3D distance of the centroid of 14 201Tl-avid peripheral tumours. Attenuation correction of gated SPECT images was performed using CT attenuation values of these fusion images. RESULTS: Gated SPECT images improved image clarity and contrast of tumour 201Tl uptakes compared with ungated images, regardless of the decreased count density due to the use of gated images. The lesion-to-normal (L/N) lung count ratios and ROI size in 18 well-circumscribed 201Tl-avid tumours were significantly higher and smaller on gated images (both P<0.0001). Gated images showed positive 201Tl uptakes in two small peripheral tumours, although negative on ungated images, and demarcated 201Tl-avid tumours from adjacent 201Tl-avid lymph node or surrounding focal 201Tl uptakes caused by other pathology, although these were not clearly demarcated on ungated images. On fusion images, gated images yielded a significantly better SPECT-CT matching compared with ungated images (P<0.0001). Fusion images accurately localized 201Tl uptakes of tumour/lymph node and other focal pathological/physiological conditions. Attenuation-corrected gated SPECT images further facilitated the detection of 201Tl uptake in small or deeply located lesions, with significantly increased L/N ratios. CONCLUSION: Gated SPECT images facilitate the detection of tumour 201Tl uptake and provide reliable SPECT-CT fusion images, which contribute to accurate interpretation and attenuation correction of Tl SPECT images.     

Gated 99Tcm-MIBI myocardial function imaging.

The introduction of the 99Tcm isonitrile perfusion agents has provided improved myocardial image quality with conventional imaging equipment allowing improved edge definition on gating. We evaluated left ventricular wall motion in 46 patients using gated 99Tcm-2-methoxy-2-methyl-isopropyl-1-isonitrile (MIBI) scintigraphy. Using a method of myocardial profiles in four axes, global and regional fractional shortening (FS) were assessed. A good correlation was found between FS in the left anterior oblique (LAO) 40 degrees projection and ejection fraction (EF) on gated radionuclide ventriculography (r = 0.81, P less than 0.001). This was improved by using FS in two planes, LAO 40 degrees and anterior (r = 0.88, P less than 0.001). There was also a good correlation between FS in two planes and EF on cine-angiography (r = 0.72, P less than 0.001). There was good intra- and interobserver agreement with the studies. Assessment of myocardial function using gated MIBI imaging and myocardial profiles provides useful additional information to the perfusion scan, thus enhancing the diagnostic usefulness of the agent.     

Effect of phase-encoding direction upon magnetic resonance image quality of the heart

In order to optimize overall cardiac image quality on MR images experienced observers were asked to rank and rate MR images of the heart. The effect of phase-encoding direction and use of cardiac triggering with and without respiratory gating was examined in three orthogonal imaging planes. Results indicate that use of both respiratory and cardiac gating yields the best images. Adequate images of the heart can be obtained without respiratory gating. The quality of images of the heart can be optimized by proper selection of the direction of the phase-encoding gradient. These are improved by using horizontal phase encoding in the sagittal plane and vertical phase encoding in transverse and coronal planes.