Breath-hold Interval Research Articles

Magnetic resonance imaging of the time course of hyperpolarized 129Xe gas exchange in the human lungs and heart

PurposeTo perform magnetic resonance imaging (MRI), human lung imaging, and quantification of the gas-transfer dynamics of hyperpolarized xenon-129 (HPX) from the alveoli into the blood plasma.Materials and methodsHPX MRI with iterative decomposition of water and fat with echo asymmetry and least-square estimation (IDEAL) approach were used with multi-interleaved spiral k-space sampling to obtain HPX gas and dissolved phase images. IDEAL time-series images were then obtained from ten subjects including six normal subjects and four patients with pulmonary emphysema to test the feasibility of the proposed technique for capturing xenon-129 gas-transfer dynamics (XGTD). The dynamics of xenon gas diffusion over the entire lung was also investigated by measuring the signal intensity variations between three regions of interest, including the left and right lungs and the heart using Welch’s t test.ResultsThe technique enabled the acquisition of HPX gas and dissolved phase compartment images in a single breath-hold interval of 8 s. The y-intersect of the XGTD curves were also found to be statistically lower in the patients with lung emphysema than in the healthy group (p < 0.05).ConclusionThis time-series IDEAL technique enables the visualization and quantification of inhaled xenon from the alveoli to the left ventricle with a clinical gradient strength magnet during a single breath-hold, in healthy and diseased lungs.Key Points• The proposed hyperpolarized xenon-129 gas and dissolved magnetic resonance imaging technique can provide regional and temporal measurements of xenon-129 gas-transfer dynamics.• Quantitative measurement of xenon-129 gas-transfer dynamics from the alveolar to the heart was demonstrated in normal subjects and pulmonary emphysema.• Comparison of gas-transfer dynamics in normal subjects and pulmonary emphysema showed that the proposed technique appears sensitive to changes affecting the alveoli, pulmonary interstitium, and capillaries.

Comparison of Dose Delivery Between Original Arc and Split Short Arcs Volumetric Modulated Arc Therapy

Delivery time for volumetric modulated arc therapy (VMAT) for treatment of tumors that can move with respiration is usually more than 2-3 minutes, longer than is possible for a single breath-hold. Original arc VMAT delivery was divided into split short arcs VMAT (SSVMAT) delivery, in order to facilitate breath-holding. This study aimed to evaluate dose delivery of SSVMAT compared to standard arc VMAT. Dose accuracies of five SSVMAT plans (3 liver, 2 lung) were evaluated. Breath-hold interval times were designed to be 10 s, 15 s, 20 s, 30 s, and 40 s. Original VMAT plans were divided into a SSVMAT plan for each of these interval times. Interruption after irradiation during each interval time was repeated for a whole VMAT delivery. Deliveries were performed with a beam modulator. A two-dimensional ionization chamber array system (2D array) was used for dose measurement. Measurement sampling time of the 2D array was set to 50 ms, and a sensitivity correction that depended on gantry angle was applied. The dose difference on the central coronal plane between SSVMAT delivery and the original VMAT delivery was analyzed. The dose at the isocenter was also compared using the center chamber of the 2D array. Pass rate was calculated from the dose difference with a criterion of 1% for a region that delivered a dose higher than 10% of the maximum dose. Mean differences in doses at the isocenter between VMAT and SSVMAT were not significant (0.5 ± 0.5% for 10 s interval, 0.2 ± 0.3% for 15 s interval, 0.2 ± 0.2% for 20 s interval, 0.0 ± 0.1% for 30 s interval, and 0.0 ± 0.1% for 40 s interval, p > 0.05). Pass rates based on dose difference were 85 ± 17% for 10 s interval, 99.9 ± 0.2% for 15 s interval, 100 ± 0% for 20 s interval, 100 ± 0% for 30 s interval, and 100 ± 0% for 40 s interval. SSVMAT with the breath-hold interval of 10 s had a significantly reduced pass rate (p = 0.017). In the present study, a practical irradiation method that can be used to divide VMAT delivery into feasible breath-hold intervals was developed. Analysis of dose verification revealed that SSVMAT deliveries with intervals of 15 s or longer provided accurate doses.

The Dosimetric Effect of Tumor Size and Position in Prone Radiation Therapy of Breast Using a Novel Stereotactic Breast Irradiation Device

ionization chamber array system (2D array) was used for dose measurement. Measurement sampling time of the 2D array was set to 50 ms, and a sensitivity correction that depended on gantry angle was applied. The dose difference on the central coronal plane between SSVMAT delivery and the original VMAT delivery was analyzed. The dose at the isocenter was also compared using the center chamber of the 2D array. Pass rate was calculated from the dose difference with a criterion of 1% for a region that delivered a dose higher than 10% of the maximum dose. Results: Mean differences in doses at the isocenter between VMAT and SSVMAT were not significant (0.5 0.5% for 10 s interval, 0.2 0.3% for 15 s interval, 0.2 0.2% for 20 s interval, 0.0 0.1% for 30 s interval, and 0.0 0.1% for 40 s interval, p > 0.05). Pass rates based on dose difference were 85 17% for 10 s interval, 99.9 0.2% for 15 s interval, 100 0% for 20 s interval, 100 0% for 30 s interval, and 100 0% for 40 s interval. SSVMAT with the breath-hold interval of 10 s had a significantly reduced pass rate (p Z 0.017). Conclusions: In the present study, a practical irradiation method that can be used to divide VMAT delivery into feasible breath-hold intervals was developed. Analysis of dose verification revealed that SSVMAT deliveries with intervals of 15 s or longer provided accurate doses. Author Disclosure: K. Noto: None. S. Ueda: None. T. Takanaka: None. A. Takemura: None.

1141 Can every other heart-beat acquisition be better for the same breath-hold interval in MR tagging sequences?

1141 Can every other heart-beat acquisition be better for the same breath-hold interval in MR tagging sequences?

Imaging of lung ventilation and respiratory dynamics in a single ventilation cycle using hyperpolarized He‐3 MRI

To image respiratory dynamics and three-dimensional (3D) ventilation during inhalation, breath-hold, and exhalation for evaluation of obstructive lung disease using a single dose of hyperpolarized (HP) He-3 during MRI. A single 2D-3D projections inside Z encoding (PRIZE)-2D acquisition was performed that consisted of a rapid 2D radial acquisition phase during inhalation of the HP He-3, a 3D acquisition phase during a breath-hold interval, and finally the same 2D radial acquisition during a forced exhalation maneuver followed by tidal breathing. The 3D PRIZE acquisition was comprised of radial sampling in the coronal plane and Fourier encoding in the patient's anterior-posterior direction. Nine patients with mild/moderate to severe asthma were studied (two individuals were studied twice) using this technique. Breath-hold and dynamic imaging results showed physiological abnormalities and were compared with results from standard spirometry, body plethysmography, and computed tomography (CT). Dynamic images depicted regions of differential gas clearance and trapping observed during and after forced exhalation that were corroborated as regions of air trapping on CT imaging. The 2D-3D PRIZE-2D acquisition allowed for 3D depiction of ventilation during a breath-hold, as well as detection of gas trapping. Imaging results were confirmed with spirometry, body plethysmography, and CT.

3D fluoroscopy with real‐time 3D non‐cartesian phased‐array contrast‐enhanced MRA

For optimized CE-MRA of the chest and abdomen, the scan time and breath-hold must be coordinated with the arrival of contrast. A 3D fluoroscopy system is demonstrated that performs real-time 3D projection reconstruction acquisition, reconstruction, and visualization using only the standard scanner hardware and operator console workstation. Unlike 2D fluorotriggering techniques, no specification of a monitoring slab or careful placement of the imaging volume is required. 3DPR data are acquired continuously throughout the examination using an eight-channel receiver and 1 s interleaved subframes. The data are reconstructed using 1 s segments for real-time monitoring with 0.8-cm isotropic spatial resolution over the entire torso, allowing full-volume axial, coronal, and sagittal MIPs to be displayed simultaneously with minimal latency. The system later uses the same scan data to generate high-spatial-resolution time-resolved sequences of the breath-hold interval. The 3D fluoroscopy system was validated on phantoms and human volunteers.

Sensitivity encoded cardiac MRI.

Imaging speed is a key factor in most cardiovascular applications of magnetic resonance imaging. Recently, simultaneous signal acquisition with multiple coils has received increasing attention as a means of enhancing scan speed in MRI. Based on this approach, the sensitivity encoding technique SENSE enables substantial scan time reduction by exploiting the inherent spatial encoding effect of receiver coil sensitivity. This work studies the benefit of sensitivity encoding for cardiovascular MRI. SENSE is applied to accelerate common breath-hold imaging as well as real-time imaging by factors up to 3.2. In the breath-hold mode with ECG triggering, this speed benefit has been used both for reducing the breath-hold interval and for improving spatial resolution. In cardiac real-time imaging without triggering and breath control, the SENSE approach has enabled significantly enhanced temporal resolution, ranging down to 13 ms (77 frames/s). Cardiac real-time SENSE is demonstrated in several modes, including real-time imaging of three parallel slices at a rate of 25 triple frames per second.

MR imaging of the small bowel with a true-FISP sequence after enteroclysis with water solution.

To evaluate a novel MR enteroclysis technique for small-bowel imaging. Twenty-one patients with suspected small-bowel disease underwent both MR and conventional enteroclysis. MR enteroclysis was performed by injecting an iso-osmotic water solution through a nasojejunal catheter with a flow rate of 80 to 150 mL/min. A maximum of 2 L of water solution was administered. A dynamic heavily T2-weighted single-shot turbo spin-echo sequence was applied in coronal orientation to monitor the bowel filling and adequate distention. Twelve 4-mm-thick slices were acquired by using a true fast imaging with steady-state precession (true-FISP) sequence during an 18-second breath-hold interval. Small-bowel distention, wall conspicuity, homogeneity of opacification, and the presence of artifacts were subjectively evaluated by two reviewers using five-point scales. Chemical shift artifacts were low and ghost artifacts were absent. Susceptibility artifacts were more prominent in the ileum; motion artifacts were low in the jejunum, ileum, and ileocecal area. Homogeneity of opacification was very good in the jejunum, good to very good in the ileum, and good in the ileocecal area. Distention was very good to excellent in the jejunum and ileum and very good in the ileocecal area. Wall conspicuity was very good to excellent in the jejunum and ileum. MR enteroclysis with the true-FISP sequence produced high-quality images of the small bowel. Further clinical studies are required to determine the clinical efficacy of the new technique compared with conventional enteroclysis.

Magnetic Resonance Angiography

Magnetic Resonance Angiography

3D MRI of the colon: methods and initial results

"Exoscopic" and endoscopic identification of colorectal pathologies via MRI. 5 patients (36-88 years), two normal and three with different colorectal pathologies (diverticular disease, polyps and carcinoma of the colon), were examined by MRI after colonoscopy. Subsequent to filling of the colon with a gadolinium-water mixture under MRI-monitoring, 3D-data sets of the colon were acquired in prone and supine positions over a 28 sec breath hold interval. Subsequently multiplanar T1-weighted 2D-sequences were acquired before and following i. v. administration of Gd-DTPA (0.1 mmol/kg BW). All imaging was performed in the coronal orientation. The 3D-data were interactively analysed based on various displays: maximum intensity projection (MIP), surface shadowed display (SSD), multiplanar reconstruction (MPR), virtual colonoscopy (VC). All of the colorectal pathologies could be interactively diagnosed by MPR. On MIP images some pathologies were missed. VC presented the morphology of colon haustra as well as of all endoluminally growing lesions in a manner similar to endoscopy. The colon masses showed uptake of contrast media and could thus be differentiated from air or faeces. The potential of CMRI in colorectal diagnosis warrants further investigation in a larger series of patients.

RARE spiral T2‐weighted imaging

Spiral imaging has a number of advantages for fast imaging, including an efficient use of gradient hardware. However, inhomogeneity -induced blurring is proportional to the data acquisition duration. In this paper, we combine spiral data acquisition with a RARE echo train. This allows a long data acquisition interval per excitation, while limiting the effects of inhomogeneity. Long spiral k-space trajectories are partitioned into smaller, annular ring trajectories. Each of these annular rings is acquired during echoes of a RARE echo train. The RARE refocusing RF pulses periodically refocus off-resonant spins while building a long data acquisition. We describe both T2-weighted single excitation and interleaved RARE spiral sequences. A typical sequence acquires a complete data set in three excitations (32 cm FOV, 192 x 192 matrix). At a TR = 2000 ms, we can average two acquisitions in an easy breath-hold interval. A multifrequency reconstruction algorithm minimizes the effects of any off-resonant spins. Though this algorithm needs a field map, we demonstrate how signal averaging can provide the necessary phase data while increasing SNR. The field map creation causes no scan time penalty and essentially no loss in SNR efficiency. Multiple slice, 14-s breath-hold scans acquired on a conventional gradient system demonstrate the performance.

Breath-hold, contrast-enhanced, three-dimensional MR angiography.

Breath-hold gadolinium-enhanced three-dimensional magnetic resonance (MR) angiography was performed with a high-performance gradient MR imaging system in 10 volunteers with no history of vascular abnormalities (breath-hold interval, 28 seconds; repetition time, 4.0 msec; echo time, 1.9 msec; 0.4 mmol gadoterate meglumin per kilogram of body weight). High-resolution three-dimensional time-of-flight angiograms of the aorta, renal arteries, pulmonary arteries, pelvic arteries, and portal venous system were successfully acquired in all cases.

Helical CT: clinical performance and imaging strategies.

For nonelectron beam systems, scan speed and image quality have reached a relative plateau of performance. Helical CT makes rapid coverage of the z axis possible, allowing scanning to occur during the optimal phase of vascular and organ enhancement. With the split breath-hold variable-mode approach, extended helical coverage across multiple anatomic regions is possible. The technique adds flexibility in choice of collimation, milliamperage, and breath-hold interval. It is easily tolerated by patients and reproducible, and the intersegment delays produce less heat loading on the x-ray tube.

Time-resolved MR imaging by automatic data segmentation.

A method for time-resolved imaging that provides a flexible trade-off between imaging time and temporal resolution is presented. It is based on a view order selection technique that automatically segments the acquired raw data into appropriate temporal frames. When used with cardiac monitoring and phase-contrast imaging, data similar to that obtained with a conventional gated phase-contrast sequence are acquired rapidly. For many applications, the temporal resolution can be reduced enough to permit imaging within a breath-hold interval, while still allowing accurate time-averaged flow quantitation. This is a general technique that can be implemented within a variety of pulse sequences and can resolve other motion cycles, including the respiratory cycle.

Hepatobiliary MR imaging: first human experience with MnDPDP.

The first human MR imaging results for the hepatobiliary contrast agent manganese(II)N,N'-dipyridoxylethylenediamine-N,N'-diacetate 5,5'-bis(phosphate) (MnDPDP) are reported. MnDPDP is a paramagnetic contrast agent specific for hepatobiliary imaging. An imaging study was performed to investigate the presence of contrast enhancement or facilitated visualization of normal structures. Twelve healthy subjects receiving MnDPDP at doses of 3, 10, or 15 mumol/kg were imaged after injection for approximately 30 minutes at 1-5-minute intervals. Transaxial abdominal images were obtained at 1.5 T in a single breath-hold interval of 21 seconds with use of a spin-echo pulse sequence (repetition time = 150 msec, echo time = 20 msec). Liver parenchyma enhancement was observed 1 minute after injection and persisted for at least 30 minutes. Clearance into the gallbladder was visualized within 15 minutes. Enhancement was dose-dependent; a dose of 10 mumol/kg produced a 75%-100% signal enhancement of the liver at 10 minutes after injection.

Segmented turboFLASH: method for breath-hold MR imaging of the liver with flexible contrast.

A method called segmented turboFLASH imaging allows high-resolution, multisection, short-inversion-time (TI) inversion-recovery (STIR), T1- or T2-weighted magnetic resonance (MR) studies of the liver to be completed within a breath-hold interval. The method was applied in a phantom and in 19 patients with hepatic lesions. Sequence comparisons were performed among segmented turboFLASH, single-shot turboFLASH, T1-weighted gradient-echo with ultrashort echo time, and T2-weighted spin-echo (SE) techniques. Signal from fat and liver could be nulled with the segmented turboFLASH method, with TIs of 10 and 300 msec, respectively; signal from these tissues could not be eliminated with the single-shot approach. Signal-difference-to-noise ratios and contrast for the best segmented sequences were comparable with those of the best T2-weighted SE and T1-weighted gradient-echo techniques. It is concluded that it is feasible to obtain breath-hold images with arbitrary tissue contrast by means of segmented turboFLASH imaging. The method may prove helpful for the detection and characterization of hepatic lesions and will likely have applications to other anatomic regions such as the chest and pelvis.