Cine Acquisition Research Articles

Influence of x‐ray pulse parameters on the image quality for moving objects in digital cardiac imaging

The image quality of a single frame in a modern cardiac imaging x-ray facility can be improved by adjusting the automatic pulse exposure parameters. The effects of acquisition rate on patient dose and the detectability of moving objects have been fully described in scientific literature. However, the influence of automatic pulse exposure parameters is still to be determined. Images of a moving wheel (with lead wires) were acquired using an H5000 Philips Integris cardiac x-ray system. Poly(methylmethacrylate) plastic samples 20 and 30 cm thick were employed as the build-up phantom to simulate a patient. The images were obtained using preset clinical parameters for cardiac imaging procedures. The signal detectability and motion blur of a contrast bar at a transversal speed in the range of 100-150 mm/s were evaluated with a cine pulse width of 3, 5, 7, and 10 ms under automatic mA kV regulation. Two levels of exposure at the image intensifier entrance were included in this study. Signal detectability was analyzed in terms of the signal-to-noise ratio (SNR) and the value of SNR2/entrance surface dose. The blurring was modeled as a Gaussian-shaped blurring function, and the motion blur was expressed in terms of the peak full width at half maximum and amplitude (apparent contrast) of the resolution functions. A contrast bar simulating a vessel in motion at the maximum velocities of typical cardiac structures was exposed. Severe loss of image quality occurred at pulse widths > or =7 ms. It is also shown that below 5 ms static nonlinearities, likely caused by the need to use a large focus for cine acquisition, dominate the blurring process.

AIR-SPAMM: alternative inversion recovery spatial modulation of magnetization for myocardial tagging

Alternate inversion recovery spatial modulation of magnetization (AIR-SPAMM) can be used either for doubling the number of tags for a given tagging encoding gradient strength or for improving tagging contrast ratio. AIR-SPAMM requires only a single acquisition and utilizes inversion pulses spaced throughout the gradient recalled echo (GRE) cine acquisition to “lock” the recovering magnetization at a desired level. The theory of AIR-SPAMM is presented along with simulations and results from phantoms. AIR-SPAMM can be used either for imaging systole as demonstrated by initial in vivo results or potentially for imaging the entire cardiac cycle in a slice-interleaved manner.

Skin dose and dose-area product values in patients undergoing intracoronary brachytherapy.

Entrance skin doses, dose-area product (DAP) values, fluoroscopy times and digital cine acquisition data were measured for 86 patients undergoing intracoronary brachytherapy procedures with beta sources, to estimate risk of skin injuries. Interventions were carried out in three dedicated X-ray interventional cardiology rooms equipped with X-ray systems operating in pulsed modes, with high filtration and edge filter options. Skin dose distribution was analysed in detail in 56 patients using slow films and thermoluminescent dosimetry. Digital recording of Digital Imaging and Communications in Medicine cine images also allowed analysis of the technical parameters used throughout the procedures. A protocol for clinical follow-up of these patients at the cardiology service is also presented, which prescribes special attention when a threshold dose is reached. Median values for DAP, fluoroscopy time and number of frames were 81.2 Gy cm(2), 17.5 min and 1569 frames, respectively, and maximum values were 323.3 Gy cm(2), 46.2 min and 3213 frames, respectively. In two cases, maximum skin doses in a procedure reached 3.5 Gy and 4.6 Gy. Comparing median values in this study, intracoronary brachytherapy involved approximately two-fold the DAP used in percutaneous transluminal coronary angioplasty procedures performed during the same period in the same catheterization laboratories, as a consequence of the need to monitor the radioactive source location used for the treatment of stenoses and the intravascular ultrasound. Special care must be paid in those cases of high dose in relation to potential patient skin injuries and late effects.

Multishot EPI-SSFP in the heart.

Refocused steady-state free precession (SSFP), or fast imaging with steady precession (FISP or TrueFISP), has recently proven valuable for cardiac imaging because of its high signal-to-noise ratio (SNR) and excellent blood-myocardium contrast. In this study, various implementations of multiecho SSFP or EPI-SSFP for imaging in the heart are presented. EPI-SSFP has higher scan-time efficiency than single-echo SSFP, as two or more phase-encode lines are acquired per repetition time (TR) at the cost of a modest increase in TR. To minimize TR, a noninterleaved phase-encode order in conjunction with a phased-array ghost elimination (PAGE) technique was employed, removing the need for echo time shifting (ETS). The multishot implementation of EPI-SSFP was used to decrease the breath-hold duration for cine acquisitions or to increase the temporal or spatial resolution for a fixed breath-hold duration. The greatest gain in efficiency was obtained with the use of a three-echo acquisition. Image quality for cardiac cine applications using multishot EPI-SSFP was comparable to that of single-echo SSFP in terms of blood-myocardium contrast and contrast-to-noise ratio (CNR). The PAGE method considerably reduced flow artifacts due to both the inherent ghost suppression and the concomitant reduction in phase-encode blip size. The increased TR of multishot EPI-SSFP led to a reduced specific absorption rate (SAR) for a fixed RF flip angle, and allowed the use of a larger flip angle without increasing the SAR above the FDA-approved limits.

Single breath-hold multi-slab and cine cardiac-synchronized gadolinium-enhanced three-dimensional angiography

The rest period of the coronary arteries has been shown to be on the order of 120–160 msec. Restriction of the acquisition window in breath-hold cardiac-synchronized gadolinium-enhanced imaging to this duration limits the amount of sampled k-space data and hence the information when compared with conventional gadolinium-enhanced imaging. Two techniques for gadolinium-enhanced cardiac-synchronized angiography were implemented that acquire additional data during the unused portions of the cardiac cycle. Data acquisition is synchronized with the heart cycle and is restricted to a short period of each heart cycle. In a single breath-hold, a multi-slab acquisition ( n = 5) allowed ECG-synchronized imaging of the entire heart or a CINE acquisition ( n = 5) provided multiple stacks of images at different phases in the cardiac cycle over a smaller area. Preliminary results acquired in healthy volunteers and patients with aortic disease indicate that additional information can be acquired without an increase in breath-hold duration or a reduction in image quality.

Kinematic MR imaging of the knee.

This is an overview of the "cine magnetic resonance (MR) imaging" system and rapid (ultra-fast) MR imaging of the knee for evaluation of injury of the cruciate ligament including its function during flexion and extension. Cine MR imaging using a gating system and a cine acquisition delineates alterations of the signal and shape of the cruciate ligaments and menisci. Rapid (ultra-fast) MR images with a single acquisition time of half second or less using a mobile knee brace and a flexible surface coil has enabled rapid acquisition of moving knee motion in multi-image frames. Visualization of the moving normal and torn anterior cruciate ligaments indicates that kinematic MR imaging of the moving knee is advantageous in evaluating the continuity and tension in the cruciate ligaments.

Segmented K-space cine breath-hold cardiovascular MR imaging: Part 1. Principles and technique.

Several well-established MR techniques are routinely used for evaluation of the heart and great vessels. Tl-weighted spin-echo images gated to the cardiac cycle provide black-blood images of the heart and vessels. Spin-echo images provide good anatomic detail, but imaging times are relatively long (approximately 5–7 min, depending on the heart rate). In addition, the images are static: only a single cardiac phase is typically acquired during this interval to avoid excessively long imaging times. Cine image acquisition often provides essential information about the cardiac chambers and flowing blood—information complementatary to the anatomic information provided on T1-weighted spin-echo images. A cine sequence of the heart consists of multiple static images that are rapidly displayed in a continuous loop. Most often, gradient-recalled echo pulse sequences are used to provide bright-blood cine images of the heart and vessels. Standard gradient-recalled echo sequences require 3–5 min to produce a cine acquisition of one to four image slices using either retrospective on prospective cardiac gating [1]. Segmented K-space cardiac sequences were described by Atkinson and Edelman [2] and allow 12–18 phases of the cardiac cycle (referred to later in this article as movie frames of a cine sequence) to be acquired in a single breath-hold using prospective cardiac gating. Segmented K-space acquisitions have been used extensively in research protocols—for example, in conjunction with MR tagging techniques [3]—although they have been less frequently used in clinical studies [4]. Commercial implementations of the pulse sequence are becoming more widely available. This essay reviews segmented K-space acquisition and illustrates different modes of application of this method for rapidly obtaining cardiac cine sequences.

Functional MRI of human brain activation combining high spatial and temporal resolution by a CINE FLASH technique.

Functional mapping of human brain activation has been accomplished at high spatial and temporal resolution (voxel size 4.9 microliter, temporal increment 100 ms). The approach was based on oxygenation-sensitive long-echo time FLASH MRI sequences synchronized to multiply repeated cycles of visual stimulation in a CINE acquisition mode. This high temporal resolution revealed that stimulus-related signal intensity changes in human visual cortex display an initial latency followed by increases extending over several seconds. Furthermore, the temporal characteristics of the complete CINE MRI signal time course depended on the absolute and relative durations of activation and control periods and, for example, caused an apparent absence of a poststimulation "under-shoot" phenomenon. Complementing hyperoxygenation due to rapid hemodynamic adjustments, these results suggest signal intensity modulation by enhanced oxygen consumption and concomitant deoxygenation during prolonged and/or repetitive stimulation.

Improved ejection fraction and flow velocity estimates with use of view sharing and uniform repetition time excitation with fast cardiac techniques.

To improve the accuracy of ventricular volume estimates and effective temporal resolution in fast cardiac acquisitions. Data sets at intermediate temporal phases were generated by means of sharing of views from two temporally adjacent data sets. A simulated model was used, and studies with patients and volunteers were conducted. View sharing was implemented in both fast gradient-echo and fast phase-contrast cine acquisitions; breath holding was used when possible. Uniform repetition time (TR) radio-frequency (RF) excitation allowed a better assessment of the end-diastolic ventricular volume. In addition, view sharing provided a better estimate of end-systolic ventricular volume in cases in which rapid changes in volume occurred at or about the temporal boundary of the source images. View sharing also provided a much smoother representation of dynamic cardiac motion when viewed in a cine loop. View sharing and uniform TR RF excitation improve the accuracy of end-systolic and end-diastolic ventricular volume measurements by improving the effective temporal resolution.

Simultaneous temporal resolution of cardiac and respiratory motion in MR imaging.

To evaluate a magnetic resonance (MR) imaging method that allows for simultaneous resolution of both the cardiac and respiratory cycles. Conventional and phase-contrast cine sequences were modified to provide additional resolution of the respiratory cycle. Data were collected in 11 healthy volunteers during MR imaging of the heart and portal vein. The imaging time was increased over that of a conventional cine acquisition by a factor equal to the number of frames in the respiratory cycle. Data were compared with those from comparable sequences in which only one motion cycle was resolved. In the heart, motion due to cardiac dynamics was separated from respiration-induced excursions. The extent of motion could be measured, and artifacts were minimized. Changes in flow rate as a function of both motion cycles were resolved and quantified in both the portal vein and superior vena cava. This method allows for simultaneous resolution of cardiac and respiratory motion cycles and helps provide a more physiologic view of the effects of cardiac and respiratory variations.

974-44 Cine Magnetization Transfer MRI: Relationship of Post MI Signal Enhancement to Regional Wall Thickening

Magnetization transfer contrast (MTC) highlights acutely infarcted regions within the left ventricle by preferentially reducing the signal intensity in normal myocardium. Since signal intensity within blood is reduced to a lesser extent. MTC also improves myocardial-blood contrast. The purpose of this study was to compare the extent of MTC signal enhancement to that of impaired regional wall thickening in patients after acute anterior MI. Six patients were imaged on a 1.5 T scanner using a 10 phase Cine acquisition in the 4chamber and 2-chamber long axis orientation, an average of 6 + 2 days post MI. The gradient recalled echo sequence (TE = 10 msec) was modified to employ a gaussian off-resonance 11500 Hz) MT pulse applied for 8.19 msec immediately prior to each of the 128 phase views. As a control, each MTC Cine was followed by an identical image sequence without the MTC pulse. Patients were imaged in a prone position over an elliptical surface coil with data acquisition synchronized to the ECG R-wave. Percent end systolic wall thickening IWT) was measured in the center of the region of MT enhancement (E). in adjacent unenhanced segments (A). and in remote normal (N) regions of the left ventricle. (N) (A) (E) ANOVA Wt(%) 416 ± 84 17.2 ± 10 * 12.9 ± 9 * p < 0.0001 * p < 0.005 versus remote normal by Scheffe sub-testing Signal intensity within normal myocardium was reduced by an average of 25.1 ± 6.6% after application of the MTC pulse, enhanced regions 6.8 ± 7.0% while blood was only reduced by 5.4 ± 3.2%. Therefore, combined functional-MTC imaging identifies a myocardial region with impaired wall thickening but normal MT contrast which may represent stunned myocardium.

Cardiac MR Imaging

Magnetic resonance (MR) imaging is becoming an important tool in diagnosing cardiovascular disease. Many technical advances have contributed to the improved capability of MR imaging in this arena. In this article, we review the technical concepts and recent advances for a variety of cardiovascular applications, including evaluation of congenital heart and great vessel disease, global cardiac function using cine acquisitions and automated ventricular volume segmentation, valvular heart disease, myocardial wall motion detection with magnetization tagging, two-dimensional and three-dimensional coronary artery imaging, and myocardial perfusion. Sequence diagrams are shown and important technical issues are discussed. Example images are shown to demonstrate the current status of research and future potential. Most results shown here are high-resolution scans acquired with new gradient coil systems, including coronary artery imaging using an in-plane resolution of 350 microns x 600 microns. This review serves as an introduction to the discussion of various clinical applications of cardiovascular MR imaging provided in this issue.

Accuracy and reproducibility of quantitative coronary arteriography using 6 and 8 french catheters with cine angiographic acquisition

To determine the suitability of 6 French catheters for quantitative coronary arteriography, the relative accuracy and reproducibility of one type of these catheters was compared to that obtained with standard 8 French catheters in 20 stenoses. Duplicate injections with polyurethane 6 French catheters were obtained using hand and power injection technique with cineangiographic acquisition (four 6 French catheter injections total per stenosis). Measurements of both percent diameter stenosis and absolute dimensions were compared to those obtained with hand injection and cine acquisition using 8 French catheters as a "gold standard." While the reproducibility of dimension determination with the 6 French catheter was generally similar to that obtained with the 8 French catheter (0.27 +/- 0.23 mm for absolute diameter and 8.1 +/- 7.4% for percent diameter stenosis), accuracy was significantly less for the 6 French catheter for measurement of absolute dimensions. Thus, while apparently well suited for serial measurements of the same stenoses, 6 French catheters may not be as accurate in the determination of absolute artery dimensions as 8 French catheters.

Cine MR imaging of valvular heart disease: display and imaging parameters affect the size of the signal void caused by valvular regurgitation.

The effects of display and imaging parameters on the measured size of the signal void representing valvular regurgitation on cine MR imaging were examined. Sixteen patients with valvular regurgitation were studied. Six cine acquisition modes were evaluated in five patients. Echo times (TEs) (8, 12, and 17 msec) and flip angles (30 degrees and 50 degrees) were varied. The variable display parameters were [Z x (blood pool signal intensity - lung signal intensity)] at window width (Z = 0.75, 1.00, 1.25) and (Y x window width + lung signal intensity) at window level (Y = 0.00, 0.25, 0.50). The area of the signal void was significantly (p less than .01) affected by the window level (2.7 +/- 0.8 cm2 at Y = 0.00, 4.4 +/- 1.1 cm2 at Y = 0.25, and 5.6 +/- 1.4 cm2 at Y = 0.50) and window width (3.6 +/- 0.9 cm2 at Z = 0.75 and 4.9 +/- 1.1 cm2 at Z = 1.25). With standardized display parameters, TE influenced the area (3.3 +/- 1.1 cm2 at 8 msec and 7.8 +/- 1.5 cm2 at 12 msec; p less than .01). Variations in the value of TE and display settings cause differences in the measured area of the regurgitant signal void. Quantification of valvular regurgitation by cine MR imaging requires strict standardization of display and imaging parameters.

Moving knee joint: technique for kinematic MR imaging.

A system for magnetic resonance imaging of the knee joint during movement was developed by using a gating system and cine acquisition. The technique was used in 10 subjects: five with no history of knee pain or injury and five with tears of the anterior cruciate ligament. The normal ligaments and menisci appeared as low-intensity structures against intermediate-intensity hyaline cartilage. The ligament tears appeared discontinuous and faint against the background of the to-and-fro moving joint fluid.

In vivo assessment of left ventricular wall and chamber dynamics during transient myocardial ischemia using cine computed tomography

Using a new computed tomographic (CT) scanner design that uses a rapidly moving focused electron beam, 50-ms CT scans were obtained at 2 axial levels simultaneously through the hearts of 6 dogs in order to analyze left ventricular (LV) wall thickness and cross-sectional chamber area after acute occlusion of the left anterior descending coronary artery (LAD). Ten or fifteen 50-ms CT scans (rate of 17 scans/s) through the middle of the left ventricle were performed in 1 second (cine acquisition) during intravenous administration of contrast medium at rest, 60 seconds after acute occlusion of the LAD, and 60 seconds after release of the occlusion. The percent extent of systolic wall thickening of the potentially ischemic anterior segment was 37 ± 15% (± standard deviation) in the control state and −5 ± 6.5% during LAD occlusion (p < 0.01). There was no significant difference in the percent change in LV luminal area from end-diastole to end-systole between the control state (50 ± 19%) compared with LAD occlusion (47 ± 21%). There were no significant differences in the extent of systolic wall thickening or LV luminal area between the control state and 60 seconds after release of occlusion. The alterations in regional myocardial function during acute ischemia are characterized by wall thinning during systole in the jeopardized segment and no significant change in global LV function. These features can be assessed by cine computed tomography during a solitary heart cycle.