Evaluation of aortic coarctation after surgical repair: role of magnetic resonance imaging and Doppler ultrasound.

OBJECTIVE--To compare the usefulness of magnetic resonance imaging (MRI) and Doppler ultrasound with that of cross sectional echocardiography and oscillometric blood pressure measurement for the evaluation of aortic coarctation after surgical repair. DESIGN--Prospective study. Aortic diameters measured by cross sectional echocardiography, MRI, and angiography (selected cases) and functional data determined by physical examination, oscillometric blood pressure measurement, and continuous wave Doppler. SETTING--Tertiary referral centre. PATIENTS--40 patients aged 2-28 years (mean 10.6 years) who had had surgical correction of aortic coarctation (mean follow up 5.7 years). RESULTS--In all patients MRI gave diameter measurements of the aortic arch and the thoracic aorta whereas in half of them cross sectional echocardiographic measurement of the isthmic region failed. The correlation coefficient for aortic diameters measured by MRI and angiography was 0.97 and that between MRI and echocardiography was 0.89. Peak velocities in the descending aorta correlated better with residual narrowing of the aortic isthmus or distal aortic arch or both than systolic blood pressure gradients between the upper and lower limbs. A peak velocity of < 2 m/s in the descending aorta during systole excluded important restenosis. Prolongation of anterograde blood flow during diastole always indicated a morphological abnormality--either important restenosis or aneurysmal dilatation. CONCLUSIONS--MRI was better than cross sectional echocardiography for imaging the aortic arch after coarctation repair and measuring its diameter. Peak velocity in the descending aorta correlated better with residual stenosis than did the systolic blood pressure gradient between the upper and lower limbs and this index could be used to indicate a need for MRI.     

Complex flow patterns in the great vessels: a review

The article reviews the applications of magnetic resonance velocity mapping based on phase shifts in the protons to quantify blood flow velocity and blood flow volume. The method can be used to study normal physiology of blood flow in the aorta and its major branches, including forward and backward flow, to measure the aortic valve function in aortic valvular disease, stenosis and regurgitation, as well as pulmonary artery flow velocities in pulmonic insufficiency and regurgitation. Superior vena cava flows, pulmonary vein flows, left-to-right shunts, atrial and ventricular pulmonary conduit flows can also be measured. Two- and three-directional velocity mapping is reviewed and can be used to study three- or four-D flows in the aorta and the major arteries in great detail.     

NMR of laser-polarized xenon in human blood

By means of optical pumping with laser light it is possible to enhance the nuclear spin polarization of gaseous xenon by four to five orders of magnitude. The enhanced polarization has allowed advances in nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI), including polarization transfer to molecules and imaging of lungs and other void spaces. A critical issue for such applications is the delivery of xenon to the sample while maintaining the polarization. Described herein is an efficient method for the introduction of laser-polarized xenon into systems of biological and medical interest for the purpose of obtaining highly enhanced NMR/MRI signals. Using this method, we have made the first observation of the time-resolved process of xenon penetrating the red blood cells in fresh human blood—the xenon residence time constant in the red blood cells was measured to be 20.4 ± 2 ms. The potential of certain biologically compatible solvents for delivery of laser-polarized xenon to tissues for NMR/MRI is discussed in light of their respective relaxation and partitioning properties.     

Complications following the ross procedure: cardiac MRI findings

Aortic valve replacement with a pulmonary autograft (ie, Ross procedure) is a technique used in selected cases for the treatment of aortic valve disease. Aware of reports describing chronic complications after the Ross procedure such as aortic insufficiency, right ventricular outlet obstruction, aortic autograft dilatation, and pulmonary allograft stenosis, cardiac magnetic resonance imaging (MRI) was performed in individuals who had a previous Ross procedure (range 2 to 10 years earlier) to determine if these complications could be visualized by MRI. This case study presents the MRI findings of 5 patients (mean age: 42.0+/-7.8 years). In each patient, complications of the Ross procedure were observed. These results suggest that cardiac MRI has the potential to become a clinically important technique for evaluating post-Ross procedure patients.     

Augmentation of oxygen transport by various hemoglobins as determined by pulsed field gradient NMR

Diffusion of oxyhemoglobin has been shown to augment the oxygen transport inside the red blood cells. Measurement of hemoglobin diffusion coefficients by pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) technique can be used for estimating this augmentation effect. Self-diffusion coefficients of polymerized and unpolymerized bovine hemoglobin (Hb) and several other proteins were measured using this technique. The Hb diffusion coefficient was used to determine the effective permeability of oxygen and augmentation of oxygen transport through samples of Hb solutions due to diffusion of oxyhemoglobin. The values compared well with our previous diffusion cell measurements of effective diffusivity and augmentation. Our NMR studies show that even at low concentrations the augmentation of oxygen transport due to diffusion can be significant. The PFG NMR technique can thus provide an accurate and easy method for measuring augmentation of oxygen transport, especially in dilute samples of Hb. The results on polyhemoglobin and high-molecular-weight hemoglobin are of both basic interest and practical value in assessing the promise and performance of hemoglobin-based blood substitutes.     

Cross sectional profiles of systolic flow velocities in left ventricular outflow tract of normal subjects.

BACKGROUND--The idea that blood passes through the left ventricular outflow tract with a flat velocity profile has recently been questioned. OBJECTIVE--To construct flow velocity profiles by magnetic resonance imaging over the whole cross sectional subaortic flow area in normal subjects. SUBJECTS--Nine people without heart disease aged 25 to 56. DESIGN--Cardiac gated cine magnetic resonance images were produced with a 1.0 T magnet perpendicular to the longitudinal axis of the left ventricular outflow tract 0.5 to 1.0 cm below the aortic annulus in mid-systole. Velocity was encoded every 30-40 ms throughout systole in the direction of flow perpendicular to the image plane. MAIN OUTCOME MEASURES--Systolic velocity-time curves reconstructed in nine different regions (area of each circle 0.2 cm2) of the subaortic flow area. The systolic peak velocity and the mean flow rate were taken as indices of regional flow. RESULTS--The spatial inhomogeneity of the peak velocity, calculated as the percentage ratio of the range of the regional measurements to their mean, averaged 18.2% (5.0%), and the inhomogeneity of the mean flow rate was 19.2% (3.5%). There were significant trends (P < 0.05) across the regional measurements towards highest peak velocities and mean systolic flow rate in the anteromedial sector of the subaortic flow area. The peak systolic velocity in the centre of the flow area averaged 98 (8) cm/s while the coincident spatial average was 94 (5) cm (P = 0.013). CONCLUSIONS--The distribution of systolic velocities across the left ventricular outflow tract is skewed towards fastest flow in the anteromedial sector of the flow area. The peak velocities measured in the centre of the flow area slightly overestimate the coincident spatial average velocities.     

Costs in follow-up of endovascularly repaired abdominal aortic aneurysms. Magnetic resonance imaging with MR angiography versus EUROSTAR protocols.

AIM: Endovascular repair of abdominal aortic aneurysms (AAA) necessitates a long-term follow-up. These patients are often old and renal insufficiency is not unusual. Cost-effectiveness needs to be addressed in evaluating methods of follow-up. The aim of this study was to compare costs of 5 years follow-up with magnetic resonance imaging with contrast enhanced three-dimensional magnetic resonance angiography (MRI/MRA) with follow-up using CT with DSA, or CTA. We also assessed the impact of contrast media induced (CMI) nephropathy on follow-up costs. METHODS: We have implemented Swedish costs of CT with DSA, and CTA on the reported follow-up examinations from the EUROSTAR progress report 2000. The costs of follow-up with CT with DSA, or CTA were compared to a follow-up protocol with MRI/MRA. A cost analysis including a risk analysis of CMI nephropathy was made between MRI/MRA and CT with DSA, or CTA. RESULTS: Excluding the risk of CMI nephropathy, the 5 years follow-up cost in Euro ( ) with MRI/MRA ( 5715) is substantially higher than CT with DSA ( 3 095) or CTA ( 3573). The cost analysis favours MRI/MRA if the risk of CMI nephropathy from CT with DSA, or CTA is more than 5%. CONCLUSION: MRI/MRA can be cost-effective for follow-up of endovascularly repaired AAA depending on the risk of CMI nephropathy for CT with DSA, and CTA. MRI/MRA should be the method of choice for patients with pre-existing renal insufficiency.     

The Role of Imaging of Flow Patterns by 4D Flow MRI in Aortic Stenosis

Aortic valve stenosis (AS) is the most prevalent valvular heart disease in developed countries and is associated with the development of severe secondary complications such as aortic dilatation and aneurysm. Emerging evidence suggests that the modified hemodynamic environment associated with AS can cause altered flow patterns in the ascending aorta associated with aortic wall remodeling and development of aortopathy. Recent advances in magnetic resonance imaging (MRI) allow for the comprehensive visualization and quantification of in vivo aortic flow pattern dynamics. In particular, the technique of 4-dimensional flow MRI offers the opportunity to derive advanced hemodynamic measures such as vorticity and helicity, wall shear stress, flow displacement, pressure gradients, viscous energy loss, and turbulent kinetic energy. This review introduces 4-dimensional flow MRI for blood flow visualization and quantification of hemodynamic metrics in the setting of aortic valve disease, with a focus on AS and associated secondary aortopathy.     

Diagnosis of thrombus and blood flow in aortic aneurysm by use of tagging cine magnetic resonance imaging

In order to diagnose thrombus and to evaluate blood flow in aortic diseases, we investigated the usefulness of tagging cine magnetic resonance imaging (MRI) in patients with aortic aneurysm and aortic dissection. Six abdominal aortic aneurysms, two aortic arch aneurysms and three aortic dissections were examined with use of tagging cine MRI. Linear tagging bands were 3 or 5 mm width and established to the long and short axial images of the aortic lesions. Tagging bands were confirmed as the low-intensity signal bands in all patients. The parts of tagging bands of the intraaortic thrombus didn't move, whereas the parts of tagging bands of the intraaortic blood flow moved and faded as time passed. Intraaortic thrombi were diagnosed in eight patients (6 abdominal aortic aneurysms, 1 aortic arch aneurysm, and 1 aortic dissection) in accordance with the stain of the parts of tagging bands. In patients with aortic dissection, the parts of tagging bands in the false lumen moved slowly, whereas the parts of tagging bands in the true lumen moved fast. Tagging cine MRI has been shown to be useful in the diagnosis of thrombus and blood flow in aortic diseases.Presented at the 36th Annual World Congress of the International College of Angiology, in New York City, New York, July 2–9, 1994     

Assessment of aortic regurgitation severity by magnetic resonance imaging of the thoracic aorta

A new method of assessing the severity of aortic regurgitationseverity by magnetic resonance imaging has been developed. Twogroups were studied: 20 controls (age=58 ± 19 years)without valvular aortic disease, and 24 patients (age=62 ±13 years) with chronic aortic insufficiency evaluated by magneticresonance and aortic root cineangiography within 1 week of eachother. A magnetic resonance sequence (TR=35 mslTE=12 mslflipangle=20°/magnet=1.5 T) was acquired in a plane containingthe thoracic aorta. A transverse saturation band 30 mm widewas positioned 30–40 mm above the aortic valve. Aorticinsufficiency was graded, the importance of end-diastolic retrogrademovement in the saturation band in the descending aorta wasnoted. Magnetic resonance was also compared to Doppler echocardiographyin 20 patients. In the controls, we found that retrograde blood flow was absent(18/20) or mild (2/20). In contrast, the presence of markedretrograde movement in a saturation band across the thoracicaorta was always associated with severe aortic regurgitation(angiographic grade III or IV). This rapid method (imaging time less than 20 min) can be appliedin most patients with aortic regurgitation and is likely tobe helpful when echocardiography is not possible or gives inconclusiveresults.     

Assessment of valvular regurgitation using cine magnetic resonance imaging coupled with phase compensation technique: comparison with Doppler color flow mapping.

To elucidate whether or not a newly developed technique in cinematic-displayed (cine) magnetic resonance imaging (MRI) can improve the semiquantitative evaluation of valvular regurgitant flow, 20 patients with valvular lesions were studied. Three pulse sequences of cine MRI, ie, standard, short echo time (TE), and rephasing scans, were compared with reference obtained by Doppler color flow mapping. Short TE technique and rephasing scan technique improved image quality remarkably as compared with standard technique. Each of the three cine MRI techniques showed good correlation with the Doppler method (p < 0.001). However, short TE and rephasing scan techniques gave a faithful estimation of the extent as compared with the Doppler method, whereas standard technique overestimated the regurgitation. Thus, cine magnetic resonance imaging with phase compensation technique can be utilized for the semiquantitative assessment of valvular regurgitation in a manner similar to that of Doppler color flow mapping.     

Measurement of portal blood flow with magnetic resonance imaging

A new method for measuring portal blood flow using magnetic resonance imaging has been developed. Flow velocities are calculated from distances that are directly visualized using a new pulse sequence. In a phantom study, the measured flow rates showed a close correlation (r = 0.9996) with actual flow rates in the range 4.7 cm/sec to 22.8 cm/sec. In a study using volunteers, portal blood flow was quickly measured (about 18 seconds) using electrocardiographic gating. These measurements were compared with those obtained by Doppler ultrasound, with which they showed a close correlation in flow velocity (r = 0.968) and flow volume (r = 0.936). This method allows reasonably accurate quantitative analysis of portal blood flow in patients in whom the Doppler method can not be used because of obesity or intestinal gas.     

Assessment of magnetic resonance velocity mapping of global ventricular function during dobutamine infusion in coronary artery disease.

BACKGROUND--Magnetic resonance imaging (MRI) is a versatile technique for examination of the cardiovascular system but only recently has assessment of myocardial ischaemia in coronary artery disease (CAD) become possible, for example by demonstrating abnormalities of regional ventricular contraction during stress. Global ventricular function during stress was assessed by MRI of aortic flow, which has not been previously attempted. DESIGN--Variables measured by MRI reflecting the effect of ischaemia on global ventricular function during dobutamine stress were correlated with thallium-201 myocardial perfusion tomography. PATIENTS--10 normal controls and 25 patients with CAD. SETTING--Tertiary cardiac referral centre. METHODS--Novel MRI sequences and analysis systems were used to measure the following variables during staged dobutamine infusion to 20 micrograms/kg/min: stroke volume, cardiac output, cardiac power output, peak flow, peak flow acceleration, aortic back flow, and flow wave velocity. Heart rate, blood pressure, double product, and maximum tolerated dobutamine dose were also measured. Multiple regression analysis was used to compare changes during stress with 201TI tomography. RESULTS--All parameters except for stroke volume and diastolic blood pressure increased in the controls. In the patients with CAD a significant relation was shown between the extent of reversible ischaemia and the change in peak flow acceleration (P < 0.00001), peak flow (P = 0.002), cardiac power output (P = 0.036), maximum dobutamine dose (P = 0.039), and systolic blood pressure (P = 0.04). Peak flow acceleration accounted for 58.4% of the variation in reversible ischaemia, and after allowing for this, only cardiac power output remained independently predictive adding a further 4.2% to the model (adjusted r2 = 0.626). A decrease in peak flow acceleration with an increase in dobutamine infusion indicated moderate or severe ischaemia (chi 2 = 10.2, P = 0.017). CONCLUSION--MRI may be used to assess variables of aortic flow during stress, which includes acceleration with high temporal resolution. Peak flow acceleration was the most sensitive indicator of the effect of ischaemia on global ventricular function.     

Diagnosis of thrombus and blood flow in aortic aneurysm using tagging cine magnetic resonance imaging

In order to diagnose thrombus and to evaluate blood flow in aortic diseases, we investigated the usefulness of tagging cine magnetic resonance imaging (MRI) in patients with aortic aneurysm and aortic dissection. Six abdominal aortic aneurysms (AAA), two aortic arch aneurysms, and three aortic dissections were examined using tagging cine MRI. Linear tagging bands were 3 or 5 mm wide and established to the long and short axial images of the aortic lesions. Tagging bands were confirmed as the low-intensity signal bands in all patients. The parts of tagging bands of the intraaortic thrombus did not move, whereas the parts of tagging bands of the intraaortic blood flow moved and faded as time passed. Intraaortic thrombi were diagnosed in eight patients (six AAA, one aortic arch aneurysm, and one aortic dissection) in accordance with the stain of the parts of tagging bands. In patients with aortic dissection, the parts of tagging bands in the false lumen moved slowly, whereas the parts of tagging bands in the true lumen moved quickly. Tagging cine MRI has been shown to be useful in the diagnosis of thrombus and blood flow in aortic diseases.Presented at the 36th Annual World Congress, International College of Angiology, New York, New York, 1994.     

Value of color Doppler estimation of regurgitant volume in patients with chronic aortic insufficiency

We studied 16 patients with chronic aortic insufficiency to compare a method for measuring regurgitant volume with color Doppler flow mapping to stroke count ratio determined by radionuclide ventriculography and to ventricular volumes assessed by two-dimensional echocardiography. A real-time color flow map of the left ventricular was obtained from an apical two- and five-chamber view and the maximal mosaic pattern of diastolic turbulent flow was planimetered as a reflection of the maximal regurgitant volume using biplane Simpson's rule. The maximal Doppler regurgitant volume evaluated by color Doppler flow mapping correlated with the stroke count ratio measured by scintigraphy (r = 0.86, SEE = 11 cc). There were significant relationships between maximal regurgitant volume measured by color Doppler and echocardiographic left ventricular end-diastolic volume (r = 0.88), left ventricular end-systolic volume (r = 0.77), and left ventricular mass (r = 0.71). Patients with larger regurgitant volumes tended to have a larger left ventricular end-diastolic volume-to-mass ratio (r = 0.56). Thus maximal aortic regurgitant volume can be estimated noninvasively with color Doppler flow mapping. The measurement appears to relate to left ventricular morphologic changes occurring in this condition and it may prove to be useful in assessing patients with chronic aortic insufficiency and in determining their long-term management.     

Doppler and echocardiographic characteristics of patients having an Austin Flint murmur

BACKGROUND. The purpose of this study was to investigate the genesis of the Austin Flint murmur using Doppler and echocardiographic imaging. METHODS AND RESULTS. A total of 51 patients having significant aortic insufficiency and an anatomically normal mitral valve were evaluated. They were divided into two groups; 30 patients had an audible Austin Flint murmur (AFM+) and 21 did not (AFM-). All patients had a complete M-mode, two-dimensional, and Doppler echocardiographic examination to characterize left ventricular size and function, motion of the mitral valve, transmitral flow velocities, direction of the aortic insufficiency jet, and severity of aortic insufficiency. There was no significant difference in severity of aortic insufficiency between groups. There was, however, a significant difference in direction of the insufficiency jet. In the AFM+ group compared with the AFM- group, for the parasternal long-axis view 24 (80%) versus eight (38%) had their insufficiency jet directed at the mitral valve, for the apical five-chamber view the values were 25 (83%) versus five (24%), and for the apical long-axis view the values were 27 (90%) versus five (24%); for all comparisons p less than 0.01. There was also a greater frequency of localized anterior mitral leaflet distortion by two-dimensional echocardiography (AFM+:23 [77%] versus AFM-:five [24%]; p less than 0.001) and a greater frequency of Doppler striations overlying the aortic insufficiency jet (AFM+:25 [83%] versus AFM-:seven [33%]; p less than 0.001). Regarding transmitral flow velocities, there was no significant difference in filling patterns or absolute velocities during early or late diastole between groups. There was no gradient by Doppler analysis or by hemodynamics (n = 26) across the mitral valve in either group. There also was no difference in the frequency of preclosure of the mitral valve (AFM+:two versus AFM-:three). Systolic function was similar in both groups, but the left ventricular end-diastolic dimension was significantly greater in the AFM+ group (6.8 +/- 0.8 cm) than in the AFM- group (6.2 +/- 0.7 cm, p = 0.008). CONCLUSIONS. The results of this study suggest that the primary factor responsible for the Austin Flint murmur is the presence of an aortic insufficiency jet directed at the anterior mitral leaflet. This, combined with the biphasic pattern of transmitral flow, distorts the shape of the anterior mitral leaflet as it opens and closes during diastole, making it shudder. The leaflet's shuddering sets up vibrations and shock waves that distort the aortic insufficiency jet, causing the observed Doppler striations and probably the sound of the murmur. There is no evidence from this study to support prior theories that have proposed functional mitral stenosis or diastolic mitral regurgitation as the source of the murmur.     

Zero-field remote detection of NMR with a microfabricated atomic magnetometer

We demonstrate remote detection of nuclear magnetic resonance (NMR) with a microchip sensor consisting of a microfluidic channel and a microfabricated vapor cell (the heart of an atomic magnetometer). Detection occurs at zero magnetic field, which allows operation of the magnetometer in the spin-exchange relaxation-free (SERF) regime and increases the proximity of sensor and sample by eliminating the need for a solenoid to create a leading field. We achieve pulsed NMR linewidths of 26 Hz, limited, we believe, by the residence time and flow dispersion in the encoding region. In a fully optimized system, we estimate that for 1 s of integration, 7 x 10(13) protons in a volume of 1 mm(3), prepolarized in a 10-kG field, can be detected with a signal-to-noise ratio of approximately 3. This level of sensitivity is competitive with that demonstrated by microcoils in 100-kG magnetic fields, without requiring superconducting magnets.     

核磁共振成像研究正常人主动脉瓣上血流速度分布的临床初探

目的:应用核磁共振成像(MRI)对国内正常人升主动脉内特定横截面上的血流速度分布进行研究,以探讨其普遍规律。方法:13例健康志愿者,均为窦性心律。应用1.5T核磁共振仪在升主动脉内、距主动脉瓣环0.5、1.0和2.0个瓣环直径处,垂直于升主动脉的层面进行成像扫描和血流参数的测量。应用血流分析软件对测得的数据进行后处理,并读取每个研究对象的核磁共振扫描图像,最后作出相应各个时相血流速度的三维图形。结果:在所有13个测试者中,在心脏收缩射血时,均有很强的信号缺失,主要分布于升主动脉外侧弯曲部分。阶段对比测量显示1.0D层面是研究升主动脉内血流速度分布的理想层面。自收缩射血的加速期至舒张早期,前向最大速度血流的偏斜呈现出从后-右-前的"右手螺旋"现象。在收缩射血的加速期和峰期,绝大部分研究对象未出现返流。结论:本研究初步探索应用MRI研究国内正常人升主动脉内特定横截面上的血流速度分布。为使这项技术成为一种安全、无创的评价人体主动脉瓣上血流速度分布的工具提供依据。     

Evaluation of pulmonary blood supply by nuclear magnetic resonance imaging in patients with pulmonary atresia

Nuclear magnetic resonance (NMR) imaging defines the blood pool without the need for contrast medium. Consequently, it may be useful for defining the pulmonary circulation in patients with pulmonary atresia, in whom opacification of these vessels can be problematic. Ten patients with pulmonary atresia were evaluated by gated NMR imaging. The morphology of the right ventricular outflow tract, the size and the course of the central pulmonary vessels and the source of the collateral supply to the lung were assessed. Central pulmonary arteries were identified and measured in 9 of the 10 patients. One patient had no detectable central pulmonary arteries. Angiography confirmed the NMR findings in all but two patients, in whom NMR scanning visualized a main pulmonary artery that was not seen on angiography. Collateral arteries arising from the aorta or the arch vessels, as well as intracardiac malformations and aortic arch anomalies, were identified in all 10 patients. In six patients with palliative surgery, NMR imaging correctly demonstrated all patent shunts. Nuclear magnetic resonance imaging appears to be an effective noninvasive technique for evaluating patients with pulmonary atresia. However, tomographic thickness and spatial resolution are still limiting factors for this technique in infants.     

Random phase detection in multidimensional NMR

Despite advances in resolution accompanying the development of high-field superconducting magnets, biomolecular applications of NMR require multiple dimensions in order to resolve individual resonances, and the achievable resolution is typically limited by practical constraints on measuring time. In addition to the need for measuring long evolution times to obtain high resolution, the need to distinguish the sign of the frequency constrains the ability to shorten measuring times. Sign discrimination is typically accomplished by sampling the signal with two different receiver phases or by selecting a reference frequency outside the range of frequencies spanned by the signal and then sampling at a higher rate. In the parametrically sampled (indirect) time dimensions of multidimensional NMR experiments, either method imposes an additional factor of 2 sampling burden for each dimension. We demonstrate that by using a single detector phase at each time sample point, but randomly altering the phase for different points, the sign ambiguity that attends fixed single-phase detection is resolved. Random phase detection enables a reduction in experiment time by a factor of 2 for each indirect dimension, amounting to a factor of 8 for a four-dimensional experiment, albeit at the cost of introducing sampling artifacts. Alternatively, for fixed measuring time, random phase detection can be used to double resolution in each indirect dimension. Random phase detection is complementary to nonuniform sampling methods, and their combination offers the potential for additional benefits. In addition to applications in biomolecular NMR, random phase detection could be useful in magnetic resonance imaging and other signal processing contexts.