Steady-state Free Precession MR Angiography Research Articles

19 Feasibility of native high-resolution 3D SSFP MR angiography for assessment of the thoracic aorta in pregnant subjects with familial aortopathies

<h3>Introduction</h3> Native magnetic resonance angiography (MRA) is recommended to assess the thoracic aorta during pregnancy, avoiding the risks of ionising radiation and contrast agent administration. This guidance is however, based only on consensus opinion supported by limited case reports (level of evidence C). <h3>Aim</h3> To evaluate the feasibility of performing native 3D steady-state free-precession (SSFP) MRA in pregnant subjects with inherited aortopathy to guide timing and mode of delivery. <h3>Methods</h3> Prospective patients (n = 15) with known thoracic aortic disease underwent native 3D-SSFP MRA at 1.5T (Avanto, Siemens) with high isotropic spatial resolution (1.3×1.3×1.3mm³) using a modified ECG-triggered sequence orientated in a sagittal-oblique plane, aligned along the aortic arch, with a respiratory navigator at the diaphragmatic level (slice thickness 2.00mm; TR/TE: 274/1.5ms). Subjects were imaged during “free breathing” adopting a “left uterine displacement” position, with a wedge under the right buttock, offloading the gravid uterus from the inferior vena cava. Aortic dimensions were measured at 7 levels by two independent blinded observers after an assessment of image quality (score 0–3: 0=poor, 3=excellent). <h3>Results</h3> Native 3D-MRA was successfully acquired in all subjects during the mid-trimester (20.6 ± 4.9wk). Subject characteristics and pregnancy outcomes are available in Table 1. Image quality was deemed excellent in 87% after a mean acquisition time of 3.1 ± 1.5min. Figure 1 provides a typical example of a 3D-MRA image. There was a high level of agreement for aortic measurements, with low intra- and inter-observer variability (ICC ranges; 0.95–0.99 and 0.92–0.96, respectively). All pregnancies reached term (≥37/40) with a mean gestation at delivery of 38.0 ± 0.5wk. Imaging surveillance in combination with satisfactory haemodynamic status permitted vaginal delivery in 60%. <h3>Conclusion</h3> Native SSFP MRA provides a robust and safe method to accurately measure the thoracic aorta in pregnant subjects with aortopathy, helping to inform decisions regarding the timing and mode of delivery.

Unenhanced MR Angiography of Renal Arteries: 51 Patients

The purpose of this research was to assess the feasibility and performance of an unenhanced 3D balanced steady-state free precession (SSFP) sequence, compared with contrast-enhanced MR angiography (CEMRA), which is the reference standard to detect and quantify renal artery stenoses (RAS). Fifty-one patients were included in this prospective study. Balanced SSFP sequence (Native) and CEMRA were performed using a 1.5-T magnet. Signal quality and stenosis grade were assessed per segment for renal arteries and for ostia of celiac trunk and superior mesenteric artery (SMA). We compared signal quality of Native and CEMRA. Sensitivity, specificity, negative predictive value (NPV), and accuracy were also calculated. Evaluation involved 114 renal arteries, 51 celiac trunks, and 51 SMAs. By use of CEMRA, 20 significant stenoses were found for renal arteries, 10 stenoses and three occlusions for celiac trunk, and three stenoses for SMA. At artery-by-artery analysis, sensitivity, specificity, accuracy, and NPV of the balanced SSFP sequence in detecting stenosis were respectively 85%, 96%, 94%, and 96% for renal arteries; 100%, 97%, 98%, and 100% for celiac trunk; and 100%, 100%, 100%, and 100% for SMA. No significant difference of signal quality was found for the entire examination and for the different segments evaluated except for hilar and intrarenal branches, which showed better signal quality on balanced SSFP sequence. The NPV results in our study suggest that unenhanced balanced SSFP MR angiography can be the first-choice imaging method to exclude RAS in patients at high risk of nephrogenic systemic fibrosis. However, when stenosis is found, other imaging modalities are necessary for better estimation.

Non-enhanced ECG-gated respiratory-triggered 3-D steady-state free-precession MR angiography with slab-selective inversion: initial experience in visualisation of renal arteries in free-breathing children without renal artery abnormality

ECG-gated non-enhanced balanced steady-state free precession (bSSFP) MR angiography requires neither breath-holding nor administration of contrast material. To investigate the image quality of free-breathing ECG-gated non-enhanced bSSFP MR angiography of renal arteries in children. Fourteen boys and seven girls (mean age, 9.7 years; range, 7 weeks-17 years) with no history of renovascular disease were included. MRI was performed at 1.5 T. Subjective image quality of axial and coronal maximum-intensity-projection reconstructions of four segments (I, aorta and renal artery ostium; II, main renal artery; III, segmental branches; IV, intrarenal vessels) was evaluated using a 4-point scale (4 = excellent, 3 = good, 2 = acceptable, 1 = non-diagnostic). Image quality was excellent for segments I (mean ± SD, 3.9 ± 0.3) and II (4.0 ± 0.1), good for segment III (3.4 ± 0.9) and acceptable for segment IV (2.3 ± 1.1 ). Mean image quality did not differ between sedated and non-sedated children. bSSFP MR angiography enables visualisation of renal arteries in children.

A study of arteries of foot by flow sensitive dephasing prepared balanced steady-state free precession MR angiography in diabetes

Objective To investigate balanced steady-state free precession with flow-sensitive dephasing magnetization preparation (FSD-bSSFP) in the assessment of arteries of foot in diabetic patients.Methods The lower-extremity peripheral arteries of 43 diabetic patients were evaluated by FSD-bSSFP no contrast MRA and contrast-enhanced MRA (CE-MRA)in. Two experienced observers assessed the image quality, degree of venous contaminated and visibility of pedal artery branches by FSD-bSSFP and CE-MRA respectively in consensus. The signal intensity( SI), signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the source images of both groups were measured and Wilcoxon and t tests were performed. Results The image score of FSD-bSSFP group was 2.7 ± 1.1 and CE-MRA was 2.6 ± 0.8, there was no statistical difference ( Z = 0. 134, P ＞ 0. 05 ). The image score of demonstration of the pedal artery branches and degree of venous contamination on FSD-bSSFP were 3.2 ± 0. 9 and 1.8 ± 0. 4 respectively which were superior to that of CE-MRA (2.5 ± 0.9 and 2.1 ± 0.8 respectively). Significant statistical difference existed between the two groups in demonstration of pedal artery branches ( Z = 5.246, P ＜ 0.05 ) and degree of venous contamination (Z =2.541 ,P ＜0.05). SNR of FSD-bSSFP was 148.6 ±26.7, CNR was 88.3 ± 19.0. SNR of CE-MRA was 148.5 ± 45.6, CNR was 121.0 ± 41.0. No statistical difference existed between SNR between two methods (t = 0.013, P ＞ 0.05 ). But CNR of CE-MRA was superior to that of FSD-bSSFP and significant statistical difference existed between these two methods ( t = 5.113, P ＜ 0.01 ). Conclusion FSD-bSSFP without contrast could be used in the evaluation of foot arteries in patients of renal dysfunction and diabetes. Key words: Magnetic resonance angiography; Diabetic foot; Balance steady-state free precession

Nonenhanced ECG-gated time-resolved 4D steady-state free precession (SSFP) MR angiography (MRA) of cerebral arteries: Comparison at 1.5T and 3T

To compare image quality of nonenhanced time-resolved 4D steady-state free precession MR angiography (4D SSFP MRA) of cerebral arteries at 1.5T and 3T. 12 healthy subjects (mean age 29.4±6.9 years) were studied at both 1.5T and 3T. Two different positions of the acquisition slab were evaluated; in one acquisition the imaging slab included the carotid siphon ("S(low)"), in the other acquisition the imaging slab was placed superior to the carotid siphon ("S(high)"). Subjective image quality of cerebral arteries was assessed independently by two readers on a 4-point scale. Relative Signal-to-Noise-Ratio (SNR) was determined for the M1 segment of the middle cerebral artery. Subjective image quality of the anterior cerebral artery (segments A1, A2) was significantly higher at 1.5T as compared to 3T, while 3T provided significantly higher image quality for segment P3 of the posterior cerebral artery. For the middle cerebral artery (segments M1-M3), image quality was significantly higher at 1.5T than at 3T when the carotid siphon was included in the acquisition slab ("S(low)"), while no significant difference was found between 1.5T and 3T with "S(high)". Relative SNR was significantly higher at 1.5T (23.1±5.1) as compared to 3T (12.1±7.8) for "S(low)" and significantly higher at 3T (29.8±5.9) than at 1.5T (24.2±3.6) for "S(high)". Our results indicate that 4D SSFP MRA should preferably be performed at 1.5T with inclusion of the carotid siphon in the acquisition slab, which might be required for the assessment of intracranial collateral flow.

Nonenhanced ECG-gated time-resolved 4D Steady-state free precession (SSFP) MR angiography (MRA) for assessment of cerebral collateral flow: comparison with digital subtraction angiography (DSA)

To evaluate a nonenhanced time-resolved 4D SSFP MRA for dynamic visualization of intracranial collateral blood flow. 22 patients (59.0 ± 11.8 years) with steno-occlusive disease of brain-supplying arteries were included in this study. 4D SSFP MRA of the intracranial arteries was acquired with 15 temporal phases and a temporal resolution of 115 ms using 1.5 T MR. Cerebral DSA served as the reference standard and was available in all patients. Nonenhanced 4D SSFP MRA allowed for detailed dynamic visualization of blood flow in the circle of Willis and its branches in 21 of 22 (95.5%) patients. Collateral flow was excluded with both 4D SSFP MRA and DSA in 4 patients. In 17 patients, DSA detected anterior collateral flow (n = 8), posterior collateral flow via the right (n = 8) and left (n = 7) posterior communicating artery as well as patent EC-IC bypasses (n = 8). 29 of 31 collateral flow pathways were visualized by 4D SSFP MRA. As compared to DSA, 4D SSFP MRA showed a high sensitivity (92.3%), specificity (100%), positive predictive value (100%) and negative predictive value (95.2%) for visualization of intracranial collateral flow. 4D SSFP MRA is a promising non-invasive imaging technique for dynamic visualization of intracranial collateral flow.

Balanced SSFP transient imaging using variable flip angles for a predefined signal profile

Variable flip angles are used in steady-state free precession (SSFP) acquisitions (e.g., time-of-flight) but to a lesser extent than in spin echo acquisitions. In balanced steady-state free precession, imaging is often assumed to occur during the steady state, which has been well described in the literature. However, in many cases, imaging occurs during the transient stage, and the use of variable flip angles can improve signal and thus image quality. Here, we present the calculation of flip angles in transient balanced steady-state free precession to generate a predefined signal profile. The signal profile was iteratively optimized to maximize the integral of the signal versus time curve. The key contribution of this work is the formulation of the flip angle as a deterministic function of the preceding and desired magnetization. Catalyzation schemes, e.g., Kaiser-windowed ramp, can be combined with variable flip angles balanced steady-state free precession to reduce signal oscillations. A uniform signal profile was used as an example to demonstrate the variable flip angle algorithm. Accuracy of the algorithm and Bloch simulations were verified with MRI phantom acquisitions. Renal angiograms were acquired using an inflow-based balanced steady-state free precession MR angiography technique; improved small-vessel depiction was observed in volunteer examinations.

Nonenhanced Free-Breathing ECG-Gated Steady-State Free Precession 3D MR Angiography of the Renal Arteries: Comparison Between 1.5 T and 3 T

The purpose of our study was to compare the image quality of free-breathing ECG-gated nonenhanced steady-state free precession (SSFP) MR angiography of renal arteries at 1.5 T and 3 T. Twenty volunteers (11 men, nine women; mean age, 23.2 +/- 2.3 years) without a history of renovascular disease participated in the study. Nonenhanced SSFP MR angiography was performed on all subjects at both 1.5 T and 3 T with a maximum interval of 2 weeks between the imaging sessions. The subjective image quality of axial and coronal maximum-intensity-projection reconstructions of four segments (1, abdominal aorta and ostium of renal artery; 2, main renal artery; 3, segmental branches outside renal parenchyma; 4, segmental branches inside renal parenchyma) was evaluated independently by two radiologists using a 4-point scale (4, excellent; 1, nondiagnostic). Relative signal-to-noise ratio, contrast-to-noise ratio, and maximum visible vessel length of the right and left renal arteries also were determined. No significant difference in image quality at 1.5 T and 3 T was found for segments 1 and 2. The mean image quality for segments 3 and 4 was significantly greater at 3 T (3.88 +/- 0.32, 3.17 +/- 0.70) than at 1.5 T (3.32 +/- 0.73, 2.09 +/- 0.81) (p < 0.001). At 3 T, the maximal vessel length of the right (9.85 +/- 0.82 cm) and left (8.3 +/- 0.79 cm) renal arteries was significantly greater than at 1.5 T (8.94 +/- 1.38 cm and 7.58 +/- 1.18 cm, respectively). Performing nonenhanced SSFP MR angiography at 3 T significantly improves visualization of peripheral renal arterial segments in healthy subjects as compared to 1.5 T.

Image quality and diagnostic accuracy of unenhanced SSFP MR angiography compared with conventional contrast-enhanced MR angiography for the assessment of thoracic aortic diseases

ObjectivesThe purpose of this study was to determine the image quality and diagnostic accuracy of three-dimensional (3D) unenhanced steady state free precession (SSFP) magnetic resonance angiography (MRA) for the evaluation of thoracic aortic diseases.MethodsFifty consecutive patients with known or suspected thoracic aortic disease underwent free-breathing ECG-gated unenhanced SSFP MRA with non-selective radiofrequency excitation and contrast-enhanced (CE) MRA of the thorax at 1.5 T. Two readers independently evaluated the two datasets for image quality in the aortic root, ascending aorta, aortic arch, descending aorta, and origins of supra-aortic arteries, and for abnormal findings. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were determined for both datasets. Sensitivity, specificity, and diagnostic accuracy of unenhanced SSFP MRA for the diagnosis of aortic abnormalities were determined.ResultsAbnormal aortic findings, including aneurysm (n = 47), coarctation (n = 14), dissection (n = 12), aortic graft (n = 6), intramural hematoma (n = 11), mural thrombus in the aortic arch (n = 1), and penetrating aortic ulcer (n = 9), were confidently detected on both datasets. Sensitivity, specificity, and diagnostic accuracy of SSFP MRA for the detection of aortic disease were 100% with CE-MRA serving as a reference standard. Image quality of the aortic root was significantly higher on SSFP MRA (P < 0.001) with no significant difference for other aortic segments (P > 0.05). SNR and CNR values were higher for all segments on SSFP MRA (P < 0.01).ConclusionOur results suggest that free-breathing navigator-gated 3D SSFP MRA with non-selective radiofrequency excitation is a promising technique that provides high image quality and diagnostic accuracy for the assessment of thoracic aortic disease without the need for intravenous contrast material.

Visualization of external carotid artery and its branches: Non–contrast‐enhanced MR angiography using balanced steady‐state free‐precession sequence and a time‐spatial labeling inversion pulse

To evaluate visibility of the external carotid artery (ECA) and its branches using three-dimensional (3D) balanced steady-state free-precession (SSFP) MR angiography with a time-spatial labeling inversion pulse (Time-SLIP), and to provide an optimal value of the inversion time (TI). Peripheral-pulse-wave-gated 3D balanced SSFP images were obtained in 20 healthy volunteers. Images with a Time-SLIP using four different TIs (600, 900, 1200, and 1500 ms) and without a Time-SLIP, referred to as sequence A to E, were acquired for each subject and compared for visibility scores of ECA system and relative signal intensity (SI) of ECA. Average Friedman rank for overall visibility was 1.63, 3.01, 3.59, 3.58, and 3.20 for sequence A to E, respectively. Sequence C and D yielded significantly higher visibility than sequence A, B, and E. The mean relative SI value was 0.97, 0.87, 0.81, 0.76, and 0.67 for sequence A to E, respectively. Balanced SSFP MR angiography with a Time-SLIP is superior to that without a Time-SLIP, showing excellent visualization of ECA system in approximately 3 min in average with sufficient background suppression including veins and salivary ducts. A TI of 1200 ms was considered to be optimal for this purpose.

Non–contrast‐enhanced MR angiography of the thoracic aorta using cardiac and navigator‐gated magnetization‐prepared three‐dimensional steady‐state free precession

To assess the usefulness of non-contrast-enhanced MR angiography using cardiac and navigator-gated magnetization-prepared three-dimensional (3D) steady-state free precession (SSFP) imaging for the diagnosis of diseases of the thoracic aorta. Twenty-two patients with diseases of the thoracic aorta were examined using a 1.5 Tesla unit. Non-contrast-enhanced MR angiography was done using parasagittal 3D SSFP combined with cardiac-gating and k-space weighted navigator-gating techniques, using T2-prepared and fat-suppression pulses. Imaging quality and the diagnostic capability of this technique were compared with the imaging quality of 2D SSFP or contrast-enhanced 3D MR angiography and with final diagnoses. Non-contrast-enhanced 3D MR angiography provided signal-to-noise and contrast-to-noise ratios of the thoracic aorta comparable to non-contrast-enhanced 2D or contrast-enhanced 3D MR angiography (P > 0.17). This imaging technique gave accurate diagnoses in 19 of the 22 patients. Non-contrast-enhanced MR angiography using cardiac and navigator-gated magnetization-prepared 3D SSFP technique was useful for the diagnosis of diseases of the thoracic aorta.

Steady‐state free precession MRA of the renal arteries: Breath‐hold and navigator‐gated techniques vs. CE‐MRA

To explore the use of breath-hold and navigator-gated noncontrast Steady State Free Precession (SSFP) MR angiography (MRA) protocols for the evaluation of renal artery stenosis (RAS). Twenty patients referred to rule out RAS were imaged using two breath-hold and one navigator-gated SSFP MRA sequences. All patients underwent contrast-enhanced MRA (CE-MRA). Two radiologists evaluated all sequences both qualitatively (blur, artifacts, reader confidence) and quantitatively (maximum stenosis). Using CE-MRA as truth, a receiver operating characteristics (ROC) curve was generated and a statistical analysis of navigator-gated SSFP (Nav SSFP) was performed. Seven patients had >50% renal artery stenosis by CE-MRA. Nav SSFP performed significantly better than either breath-hold SSFP technique in terms of blur, artifacts, and reader confidence. Using a 50% threshold for stenosis, sensitivity for detecting RAS was 100%, with a specificity of 85% and a negative predictive value of 100%. The average mean stenosis difference between Nav SSFP and CE-MRA was 9 +/- 9%. Nav SSFP outperformed breath-hold SSFP in measures of image quality and reader confidence. Sensitivity and negative predictive value for detecting RAS with Nav SSFP was perfect, with an acceptable specificity of 85%. This suggests further study is warranted to evaluate Nav SSFP as a noncontrast screening technique for renal artery stenosis.

Gadolinium-based MR Contrast Agents and Nephrogenic Systemic Fibrosis

Phillip H. Kuo, MD, PhD Emanuel Kanal, MD Ali K. Abu-Alfa, MD Shawn E. Cowper, MD Nephrogenic systemic fibrosis (NSF), described in 2000 (1), is an emerging systemic disorder characterized by widespread tissue fibrosis. Originally known as nephrogenic fibrosing dermopathy because of its dominant cutaneous findings, the nomenclature was revised in recent years to reflect an increased understanding of its systemic effects (1,2). While the precise cause of NSF remains a mystery, it is known to occur only in patients with renal disease– generally in those requiring dialysis. NSF may develop rapidly and can sometimes result in patients becoming confined to a wheelchair within a few weeks. More commonly, the skin thickening is insidious and can be confused clinically with peripheral edema. Pathophysiologically, NSF results in increased tissue deposition of collagen, commonly resulting in thickening and hardening of the skin of the extremities and often culminating in immobility and contractures of the joints. In some patients, there is clinical involvement of other tissues (lung, skeletal muscle, heart, diaphragm, esophagus, etc), although the patient may not be clinically symptomatic (3). While NSF sometimes stabilizes, it rarely spontaneously remits. No consistently effective therapy exists, although rapid correction in renal function (by medical or surgical means) generally results in a cessation of progression and often in a reversal of symptoms (4). With renal dysfunction at the core of this condition, the possibility that renally excreted endogenous or exogenous substances may be triggering NSF has been of great interest. Since NSF appears not to have existed prior to 1997, suspicion that a recently introduced agent might be the culprit has been rampant, but investigation by several authors and by the Centers for Disease Control and Prevention has so far failed to identify a single causative medication (3). Of great interest, the author of a recent article (5) has suggested that administration of intravenous contrast material for magnetic resonance (MR) imaging (ie, gadolinium chelates) has been associated with a small cluster of patients with NSF in Austria (five of nine imaged patients). A Web-based medical advisory originating in Denmark claims that, since January 2002, approximately 400 patients with severely impaired renal function were administered gadolinium-based MR contrast material; 20 patients (5%) subsequently were diagnosed with NSF (6). Other unpublished U.S. experience (S.E.C., October 2006) suggests an approximate incidence of 3% for the development of NSF in the setting of severe renal failure and administration of intravenous contrast material for MR imaging. An international NSF registry at Yale University (New Haven, Conn) maintains records on over 215 patients with NSF worldwide. A survey now underway has revealed that more than 95% of all NSF patients surveyed (currently approximately 100) have been exposed to a gadolinium chelate within 2–3 months prior to disease onset. The majority of the patients were being maintained with dialysis. However, a number of patients with impaired renal function have been reported to the registry, the severity of whose disease has been difficult to determine retrospectively. To the best of our knowledge, the overwhelming majority of known NSF cases at this point ( 90%) represent patients who had previously received gadodiamide (Omniscan; GE Healthcare, Princeton, NJ) (7). Nevertheless, there have been reports of NSF cases associated with other agents. As of October 26, 2006, there have been a total of 57 cases of NSF associated with prior gadolinium-based MR contrast agent administration reported to the U.S. Food and Drug Administration (FDA) Published online before print 10.1148/radiol.2423061640