FLAIR imaging for multiple sclerosis: a comparative MR study at 1.5 and 3.0 Tesla

The purpose of this study was (1) to identify the optimal TE for FLAIR-imaging at 3.0 T assessing three different echo times qualitatively and quantitatively and (2) to evaluate the diagnostic efficacy of high-field 3.0-T FLAIR imaging in comparison to conventional 1.5-T MRI in patients with multiple sclerosis (MS). Twenty-two patients with clinically definite MS underwent axial FLAIR imaging at 1.5 and 3.0 T. In 15 of these patients further FLAIR images with a TE of 100, 120 and 140 ms were acquired at 3.0 T. Imaging protocols were modified for 3.0 T using the increased SNR to acquire more and thinner slices while maintaining a comparable scan time. FLAIR images of either different TEs or different field strengths were ranked for each patient qualitatively by two observers. Signal intensity measurements were obtained in the gray and white matter, CSF and representative white matter lesions (WML). At 3.0 T, a TE of 100 and 120 ms proved superior in all qualitative categories when compared to 140 ms. In the quantitative assessment CNR of WML was highest for 120 ms (CNR: 19.8), intermediate for 100 ms (17.2) and lowest for 140 ms (15.3) (P<0.003). For lesion conspicuity and overall image quality, 3.0 T was judged superior to 1.5 T, whereas no difference was found for gray-white differentiation and image noise. With regard to artifacts, 3.0 T was inferior to 1.5 T. The CNR for WML was slightly lower at 3.0 T, but the difference was not significant (22.6 vs. 28.0, P=ns). However, significantly more WML were detected at 3.0 T than at 1.5 T (483 vs. 341, P<0.0001). The optimal echo time for FLAIR imaging at 3.0 T is 120 ms due to the significantly higher CNR of WML. By trading the higher SNR at 3.0 T for better spatial resolution, nearly the same CNR level could be maintained, increasing lesion detectability at 3.0 T compared to 1.5 T. Thus, high-field MRI may further strengthen the role of MRI as the most sensitive paraclinical test for the early diagnosis of MS.     

Whole-body magnetic resonance angiography at 3.0 Tesla

The quality of magnetic resonance (MR) angiography could be substantially improved over the past several years based on the introduction and application of parallel imaging, new sequence techniques, such as, e.g., centric k-space trajectories, dedicated contrast agents, and clinical high-field scanners. All of these techniques have played an important role to improve image resolution or decrease acquisition time for the dedicated examination of a single vascular territory. However, whole-body MR angiography may be the application with the potential to profit most from these technical advances. The present review article describes the technical innovations with a focus on parallel imaging at high field strength and the impact on whole-body MR angiography. The clinical value of advanced whole-body MR angiography techniques is illustrated by characteristic cases.     

3.0 Tesla vs 1.5 Tesla breast magnetic resonance imaging in newly diagnosed breast cancer patients

AIM:To compare 3.0 Tesla(T) vs 1.5T magnetic resonance(MR) imaging systems in newly diagnosed breast cancer patients.METHODS:Upon Institutional Review Board approval,a Health Insurance Portability and Accountability Actcompliant retrospective review of 147 consecutive 3.0T MR examinations and 98 consecutive 1.5T MR examinations in patients with newly diagnosed breast cancer between 7/2009 and 5/2010 was performed.Eleven patients who underwent neoadjuvant chemotherapy in the 3.0T group were excluded.Mammographically occult suspicious lesions(BIRADS Code 4 and 5) additional to the index cancer in the ipsilateral and contralateral breast were identified.Lesion characteristics and pathologic diagnoses were recorded,and results achieved with both systems compared.Statistical significance was analyzed using Fisher’s exact test.RESULTS:In the 3.0T group,206 suspicious lesions were identified in 55%(75/136) of patients and 96%(198/206) of these lesions were biopsied.In the 1.5T group,98 suspicious lesions were identified in 53%(52/98) of patients and 90%(88/98) of these lesions were biopsied.Biopsy results yielded additional malignancies in 24% of patients in the 3.0T group vs 14% of patients in the 1.5T group(33/136 vs 14/98,P = 0.07).Average size and histology of the additional cancers was comparable.Of patients who had a suspicious MR imaging study,additional cancers were found in 44% of patients in the 3.0T group vs 27% in the 1.5T group(33/75 vs 14/52,P = 0.06),yielding a higher positive predictive value(PPV) for biopsies performed with the 3.0T system.CONCLUSION:3.0T MR imaging detected more additional malignancies in patients with newly diagnosed breast cancer and yielded a higher PPV for biopsies performed with the 3.0T system.     

Evolution of VX2 carcinoma in rabbit tibia: magnetic resonance imaging with pathologic correlation

OBJECTIVE: To evaluate the evolution of a metastatic bone tumor model with MRI-pathology correlation. MATERIALS AND METHODS: VX2 carcinoma was implanted into the tibiae of 20 rabbits. The rabbits were divided into four groups of five (Groups I-IV). MRI was repeated at 1-week interval up to the fourth week, including sagittal T1-weighted image (T1WI), T2-weighted image (T2WI), gadolinium-enhanced fat-suppressed T1WI (GdT1WI), and diffusion-weighted image (DWI). Each group was sacrificed after the imaging, then histological examination for the tibiae with an implanted tumor was performed and MRI-pathologic correlation was done. RESULTS: On MRI-pathology correlation, the corresponding findings were as follows; low SI on T1WI, T2WI-tumor cells, fibrosis (1 week); central low SI on T1WI, T2WI, GdT1WI -tumor cells with fibrosis and necrosis; peripheral high SI on T2WI, DWI, GdT1WI-edema, fibrosis (2 weeks); heterogeneous SI with central low SI on T2WI, DWI-tumor cell nests with extensive necrosis, fibrosis; high SI on T2WI along periosteum-periosteal reaction; high SI around low SI and in bone marrow on T2WI, DWI, GdT1WI-edema, fibrosis; low SI on T1WI in surrounding bone marrow-tumor extension (3-4 weeks). CONCLUSION: The evolution of VX2 carcinoma model was well depicted on MR imaging. Necrosis and extent of tumor were best depicted on enhanced, fat-suppressed T1-weighted images. Heterogeneity of the tumor, peripheral edema, and fibrosis were represented well on T2-weighted images. Diffusion-weighted imaging could have a role in depicting necrosis in the evaluation of bone tumor.     

Time-resolved echo-shared parallel MRA of the lung: observer preference study of image quality in comparison with non-echo-shared sequences

The aim of this study was to evaluate the image quality of time-resolved echo-shared parallel MRA of the lung. The pulmonary vasculature of nine patients (seven females, two males; median age: 44 years) with pulmonary disease was examined using a time-resolved MRA sequence combining echo sharing with parallel imaging (time-resolved echo-shared angiography technique, or TREAT). The sharpness of the vessel borders, conspicuousness of peripheral lung vessels, artifact level, and overall image quality of TREAT was assessed independently by four readers in a side-by-side comparison with non-echo-shared time-resolved parallel MRA data (pMRA) previously acquired in the same patients. Furthermore, the SNR of pulmonary arteries (PA) and veins (PV) achieved with both pulse sequences was compared. The mean voxel size of TREAT MRA was decreased by 24% compared with the non-echo-shared MRA. Regarding the sharpness of the vessel borders, conspicuousness of peripheral lung vessels, and overall image quality the TREAT sequence was rated superior in 75–76% of all cases. If the TREAT images were preferred over the pMRA images, the advantage was rated as major in 61-71% of all cases. The level of artifacts was not increased with the TREAT sequence. The mean interobserver agreement for all categories ranged between fair (artifact level) and good (overall image quality). The maximum SNR of TREAT did not differ from non-echo-shared parallel MRA (PA: TREAT: 273±45; pMRA: 280±71; PV: TREAT: 273±33; pMRA: 258±62). TREAT achieves a higher spatial resolution than non-echo-shared parallel MRA which is also perceived as an improved image quality.     

Fluid Attenuated Inversion Recovery (FLAIR) Imaging of the Normal Brain: Comparisons between Under the Conditions of 3.0 Tesla and 1.5 Tesla

Objective

The aim of this study was to evaluate the differences in normal brain MRI findings between under 3.0 Tesla (T) and 1.5T MRI conditions with the use of the fluid attenuated inversion recovery (FLAIR) sequences.

Materials and Methods

Eleven normal adults underwent imaging with the use of the FLAIR sequences on both 1.5T and 3.0T scanners. Two neuroradiologists compared the signal intensity (SI) of the centrum semiovale (CS), pulvinar thalami (PT) and normal iron deposit structures (IDSs) on the 3.0T and 1.5T FLAIR images, and they evaluated three MRI findings qualitatively: high SI of CS; low SI of PT; low SI of IDS. We also evaluated signal-to-noise ratios (SNRs) for the CS, PT, red nucleus and cerebellar dentate nucleus on the FLAIR images.

Results

Based on qualitative analyses, the 3.0T FLAIR images showed all three MRI findings for all cases. Low SI for the PT in seven cases (64%), high SI of the CS in one case (9%) and low SI of the cerebellar dentate nucleus in one case (9%) were visualized only on 3.0T FLAIR images. The mean SNRs of the PT, red nucleus and dentate nucleus in patients where 3.0T FLAIR imaging was performed were significantly lower as compared with the SNRs on 1.5T FLAIR images. The SNR of the CS was not significantly different between under the two magnetic field strengths (p > 0.05).

Conclusion

We have demonstrated that normal, high and low SIs of the CS, PT and IDS on 3.0T FLAIR images were depicted more frequently and more prominently as compared with those on 1.5T FLAIR images in normal adult brains.     

Basilar artery atherosclerotic plaques distribution in symptomatic patients: A 3.0 T high-resolution MRI study

Purpose

To investigate basilar artery atherosclerotic plaque distribution characteristics in symptomatic patients using 3.0 T high-resolution MRI.

Materials and methods

Thirty-eight patients with recent ischemic strokes or transient ischemic attacks were included. Conventional angiographic luminal imaging of these patients showed at least 30% basilar artery stenosis. Patients then underwent basilar artery high-resolution MRI examinations (T2WI, T1WI and post-contrast enhanced T1WI in short axial and long axial views). The narrowest lumen plaque distribution was evaluated by cross-section division into four equal arcs (right, ventral, left and dorsal arcs) on the short axial T2-weighted images. The percent plaque fraction was calculated as arc plaque area/luminal area × 100, with each compared by analysis.

Results

The basilar artery lumens and walls were clearly shown in all 38 patients. The median plaque area sizes were 2.73 mm² (range: 1.04–5.29 mm²) on the ventral wall, 0.59 mm² (range: 0–1.50 mm²) on the left wall, 0.87 mm² (range: 0–2.68 mm²) on the dorsal wall, and 0.36 mm² (range: 0–1.80 mm²) on the right wall. The mean plaque fraction percentages were 21.6% (range: 7.9–34.0%) on the ventral wall, 4.6% (range: 0–10.0%) on the left wall, 6.3% (range: 0–16.3%) on the dorsal wall, and 2.6% (range: 0–12.9%) on the right wall. On the ventral wall, the plaque fraction percentage was significantly greater than the remaining three arcs (P = .000).

Conclusions

Basilar artery atherosclerotic plaques were mainly distributed at the ventral site of the artery. High-resolution MR examination may provide helpful information to minimize endovascular therapy risk complications in basilar artery atherosclerotic disease.     

Comparison of image quality in magnetic resonance imaging of the knee at 1.5 and 3.0 Tesla using 32-channel receiver coils

We examined to what degree the visualization of anatomic structures in the human knee is improved using 3.0-T magnetic resonance imaging (MRI) and many element RF receive coils as compared to 1.5 T. We imaged 20 knees at 1.5 and 3.0 T using T2-weighted STIR, T2-weighted gradient echo, T1-weighted spin-echo, true-FISP and T2-weighted fast spin echo techniques in conjunction with 32-element RF coil arrays. The 3.0-T examination was considerably faster than its 1.5-T counterpart. A superior subjective visibility at 3.0 T vs 1.5 T was found in 27 of 50 evaluated structures (meniscus, ligaments) with the exception of true-FISP techniques. The 3.0-T examination provided a better visibility (evaluated by blinded consensus-reading by two radiologists) of small structures such as the ligamentum transversum genu. Also, cartilage was better delineated at 3.0 T. A 23% increased average signal-to-noise ratio as assessed using a temporal filter was observed at 3.0 T as compared to 1.5 T. At 3.0 T, imaging of the human knee is faster and results in a subjective visibility of anatomic structures that is superior to and competitive with 1.5 T.     

A case of scapulothoracic dissociation with brachial plexus injury: magnetic resonance imaging findings

Scapulothoracic dissociation is defined as violent lateral or rotational displacement of the shoulder girdle from its thoracic attachments with severe neurovascular injury. We describe the radiographic and associated magnetic resonance (MR) imaging findings of a case of scapulothoracic dissociation with brachial plexus injury in a 17-year-old man, and include a review of the relevant literature.     

The magnetic resonance imaging appearance at 1.5 Tesla of cartilaginous tumors involving the epiphysis

Three cases of lytic, calcified epiphyseal lesions with plain film and computed tomography features suggestive of chondroblastoma were imaged by magnetic resonance imaging. Histopathologic correlation was obtained in each case. Two cases of chondroblastoma showed low signal intensity on both short (TR600/TE20ms) and long (TR2500/TE80ms) spin echo (SE) images. The third case, a clear cell chondrosarcoma, demonstrated increased signal intensity on moderately T2 weighted (TR2500/TE40ms) images. These findings suggest that magnetic resonance imaging may be helpful in distinguishing these lesions.     

Fat suppression gradient-echo magnetic resonance imaging of experimental articular cartilage lesions: comparison between phase-contrast method at 0.23T and chemical shift selective method at 1.5T

PURPOSE: To evaluate the diagnostic performance of a newly developed single-scan phase-contrast water-fat imaging technique for fat suppression at 0.23T open magnet, compared to the conventional chemical shift selective fat suppression method at 1.5T, in the detection of experimental articular cartilage lesions. MATERIALS AND METHODS: Sixty regions of 20 knee joint specimens of pigs with artificially created articular cartilage lesions were examined with 0.23T and 1.5T MR scanners. Sagittal fat-suppressed three-dimensional gradient-echo (3D GRE) images, obtained with the phase-contrast method at 0.23T, and fat-suppressed three-dimensional spoiled gradient recalled echo (3D SPGR) images, obtained with a chemical shift selective method at 1.5T, were evaluated. Diagnostic performance was analyzed. The conspicuity of the lesions, the amount of artifacts, and the uniformity of fat suppression were evaluated. The contrast-to-noise (CNR) values of cartilage-to-bone marrow, and cartilage-to-infrapatellar fat were calculated. RESULTS: At 0.23T, sensitivity and specificity were 80% and 95% for partial cartilage lesions (grade 2), and 91% and 100% for full-thickness lesions (grade 3). At 1.5T, sensitivity and specificity were 85% and 95% for grade 2 lesions, and 96% and 97% for grade 3 lesions. No significant difference was detected in the conspicuity of lesions. The uniformity of fat suppression was more constant with 3D SPGR images compared to 3D GRE images. More susceptibility artifacts, derived from the procedure of creating lesions, were detected at 1.5T. The cartilage-to-fat CNRs were significantly higher with high-field images. CONCLUSION: Phase-contrast method for fat suppression at 0.23T is a useful technique in detecting articular cartilage lesions.     

The role of magnetic resonance imaging and ultrasound in patients with adnexal masses

AIMS: To evaluate the accuracy of ultrasonography (US) and magnetic resonance imaging (MRI) in characterizing adnexal masses, and to determine which patients may benefit from MRI. METHODS: We prospectively studied 72 women (mean age 53 years, range 19 to 86 years) with clinically suspected adnexal masses. A single experienced sonographer performed transabdominal and transvaginal greyscale spectral and colour Doppler examinations. MRI was carried out on a 1.5T system using T1, T2 and fat-suppressed T1-weighted sequences before and after intravenous injection of gadolinium. The adnexal masses were categorized as benign or malignant without knowledge of clinical details, according to the imaging features which were compared with the surgical and pathological findings. RESULTS: For characterizing lesions as malignant, the sensitivity, specificity and accuracy of MRI were 96.6%, 83.7% and 88.9%, respectively, and of US were 100%, 39.5% and 63.9%, respectively. MRI was more specific (p<0.05) than US. Both MRI and US correctly diagnosed 17 (24%) cases with benign and 28 (39%) cases with malignant masses. MRI correctly diagnosed 19 (26%) cases with benign lesion(s), which on US were thought to be malignant. The age, menopausal status and CA-125 levels in these women made benign disease likely, but US features were suggestive of malignancy (large masses and solid-cystic lesions with nodules). CONCLUSION: MRI is more specific and accurate than US and Doppler assessment for characterizing adnexal masses. Women who clinically have a relatively low risk of malignancy but who have complex sonographic features may benefit from MRI.     

Cardiac magnetic resonance parallel imaging at 3.0 Tesla: technical feasibility and advantages

PURPOSE: To quantify changes in signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), specific absorption rate (SAR), RF power deposition, and imaging time in cardiac magnetic resonance imaging with and without the application of parallel imaging at 1.5 T and 3.0 T. MATERIALS AND METHODS: Phantom and volunteer data were acquired at 1.5 T and 3.0 T with and without parallel imaging. RESULTS: Doubling field strength increased phantom SNR by a factor of 1.83. In volunteer data, SNR and CNR values increased by factors of 1.86 and 1.35, respectively. Parallel imaging (reduction factor = 2) decreased phantom SNR by a factor of 1.84 and 2.07 when compared to the full acquisition at 1.5 T and 3.0 T, respectively. In volunteers, SNR and CNR decreased by factors of 2.65 and 2.05 at 1.5 T and 1.99 and 1.75 at 3.0 T, respectively. Doubling the field strength produces a nine-fold increase in SAR (0.0751 to 0.674 W/kg). Parallel imaging reduced the total RF power deposition by a factor of two at both field strengths. CONCLUSIONS: Parallel imaging decreases total scan time at the expense of SNR and CNR. These losses are compensated at higher field strengths. Parallel imaging is effective at reducing total power deposition by reducing total scan time.     

Magnetic resonance imaging of the hip with a pelvic phased-array surface coil: a technical note

Objective. The aim of this study was to assess the capability of high-resolution images obtained with a commercially available pelvic phased-array surface coil to demonstrate normal hip anatomy. Design. We retrospectively analyzed the oblique coronal magnetic resonance (MR) images of hips of 36 consecutive patients acquired on a 1.5-T clinical imager using a pelvic phased-array coil as a receiver, a 16–20 cm field of view, and 5 mm slice thickness. Patients. Thirty-six patients were studied, age 15–81 years. There were 20 males and 16 females. Results and conclusions. The articular cartilage, cortex, superior labrum, and iliofemoral ligament were well visualized on proton density weighted fat saturation (PDF) images. The femoral and obturator vessels, obturator nerve, and various muscles were easily seen on T1-weighted images. High-resolution imaging of the hip is achievable in a reasonable amount of time using newer phased-array surface coils and may play an increasing role in the future evaluation of hip disorders.     

Association of carotid atherosclerotic plaque features with acute ischemic stroke: A magnetic resonance imaging study

Background and purpose

It remains unclear whether direct vessel wall imaging can identify carotid high-risk lesions in symptomatic subjects and whether carotid plaque characteristics are more effective indicators for cerebral infarct severity than stenosis. This study sought to determine the associations of carotid plaque characteristics by MR imaging with stenosis and acute cerebral infarct (ACI) sizes on diffusion weighted imaging (DWI).

Materials and methods

One hundred and fourteen symptomatic patients underwent carotid and brain MRI. ACI volume was determined from symptomatic internal carotid artery territory on DWI images. Ipsilateral carotid plaque morphological and compositional characteristics, and stenosis were also determined. The relationships between carotid plaque characteristics, stenosis and ACIs size were then evaluated.

Results

In carotid arteries with 30–49% stenosis, 86.7% and 26.7% were found to have lipid-rich necrotic core (LRNC) and intraplaque hemorrhage, respectively. Furthermore, 45.8% of carotid arteries with 0–29% stenosis developed LRNCs. Carotid morphological measurements, such as % wall volume, and the LRNC size were significantly associated with ipsilateral ACIs volume before and after adjustment for significant demographic factors (age and LDL) or stenosis in patients with carotid plaque (all p < 0.05).

Conclusions

A substantial number of high-risk plaques characterized by vessel wall imaging exist in carotid arteries with lower grade stenosis. In addition, carotid plaque characteristics, particularly the % wall volume and LRNC size, are independently associated with cerebral infarction as measured by DWI lesions. Our findings indicate that characterizing atherosclerotic plaque by MR vessel wall imaging might be useful for stratification of plaque risk and infarction severity.     

MR imaging of patients with localisation-related seizures: initial experience at 3.0T and relevance to the NICE guidelines

The purpose of this study is to describe our initial experience of imaging adults with localisation-related epilepsy using MR imaging at 3.0T. We discuss the findings in the context of the recently released NICE guidelines that provide detailed advice on imaging people with epilepsy in the UK. 120 consecutive people over the age of 16 years with localisation-related epilepsy were referred for clinical MR examinations from a regional neuroscience centre in England. None of the people had had MR examinations prior to the present study. High resolution MR imaging was performed taking advantage of the high field strength and high performance gradients of the system. Two experienced neuroradiologists reported on the examinations independently and the presence and type of pathology was recorded. There was complete agreement between the two reporters in all 120 cases. The overall frequency of abnormalities shown by MR was 31/120 (26%) and the commonest abnormality shown was mesial temporal sclerosis found in 10/120 (8%). Tumours were shown in 4/120, all of which appeared low grade as judged by imaging criteria. Epilepsy is the commonest neurological condition and demands a significant resource in order to provide good care for sufferers. Recent guidelines published in the UK have suggested that the majority of people with epilepsy should receive brain MR as part of their routine assessment. Our work shows that using the most sophisticated MR imaging in a highly selected population there is a modest pick-up rate of brain abnormalities. If a widespread epilepsy-imaging programme is started the detection rate is likely to be much lower. Although MR is acknowledged to be a reliable way of detecting pathology in people with epilepsy there is a dearth of information studying the health economics of imaging epilepsy in relation to patient management and outcomes.     

脊柱转移瘤的3．0T氢质子磁共振波谱初步观察与分析

目的：初步探讨3．0T脊柱转移瘤氢质子磁共振波谱（^1H-MRS）特点。方法：前瞻性分析23例经临床证实的脊柱转移瘤的^1H-MILS的变化,同时以25例健康组椎体的^1H-MRS作对照,定量分析感兴趣椎体的脂峰与水峰的比率（LWR）及脂肪百分含量（FF％）,并作两组统计学分析。结果：脊柱转移瘤病变椎体MRS脂峰明显降低,水峰略增高,转移瘤组平均LWR为（0．039±0．025）,平均FF％为（3．66±8．66％）,对照组椎体平均LWR为（0．64±0．20）,平均FF％为（37．91±8．66％）,转移瘤组LWR和FF％明显低于正常对照组（t=14．7,P〈0．01和t=19．1,P〈0．01）。结论：脊柱转移瘤^1H-MRS示LWR及FF％值明显降低,与健康对照组比较具有显著性差异,^1H-MRS可以量化的方式分析病变椎体代谢物的变化。     

Myocardial tagging and strain analysis at 3 Tesla: comparison with 1.5 Tesla imaging

PURPOSE: To determine whether imaging at 3 T could improve and prolong the tag contrast compared to images acquired at 1.5 T in normal volunteers, and whether such improvement would translate into the ability to perform strain measurements in diastole. MATERIALS AND METHODS: Normal volunteers (N = 13) were scanned at 1.5 T (GE Signa CV/i) and 3.0 T (GE VH/i). An ECG-triggered, segmented k-space, spoiled-gradient-echo grid-tagged sequence was used during cine acquisition. Tag contrast was determined by the difference of the mean signal intensity (SI) of the tagline to the mean SI of the myocardium divided by the standard deviation (SD) of the noise (CNR(tag)). Matched short-axis (SA) slices were analyzed. Strain measurements were performed on images using a 2D strain analysis software program (harmonic phase (HARP)). RESULTS: The average CNR(tag) over the cardiac cycle was superior at 3 T compared to 1.5 T for all slices (3 T: 23.4 +/- 12.1, 1.5 T: 9.8 +/- 8.4; P < 0.0001). This difference remained significant at cycle initiation, end-systole, and the end R-R interval (at cycle termination: 3 T = 14.0 +/- 11.0 vs. 1.5 T = 4.4 +/- 3.5; P < 0.01). Strain measures were obtainable only in early systole for 1.5 T images, but were robust throughout the entire R-R interval for 3 T images. CONCLUSION: Imaging at 3 T had a significant benefit for myocardial tag persistence through the cardiac cycle. The improvement allowed strain analysis to be performed into diastole.     

3.0 Tesla magnetic resonance angiography of endovascular aortic stent grafts: phantom measurements in comparison with 1.5 Tesla

RATIONALE AND OBJECTIVES: This study evaluated different stent grafts by 3 T magnetic resonance angiography (MRA) with respect to lumen visibility, susceptibility-induced signal loss, and type of stent artifacts compared with 1.5 T MRA in a phantom model. METHODS: Six different stent-grafts (tube: n = 3, bifurcated: n = 3) were evaluated by 3 T and 1.5 T MRA using a tube phantom. MRA was performed using T1-weighted sequences at both systems with comparable parameters (3T: TR 5.4/TE 2.0/FA 30 degrees, 1.5 T: TR 6.2/TE 2.2/FA 30 degrees). A blind study of the image quality, including artifacts, was performed by 3 radiologists. Furthermore, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) values were calculated. Statistical analysis was performed with Student's t test (P < 0.05). RESULTS: One Elgiloy stent graft showed almost a complete intraluminal signal loss at 1.5 and 3 T. All other models could be evaluated by both systems by MRA, resulting in a favorable lumen visibility (score: 1) for prostheses made of nitinol. Scores for overall image quality and artifacts were the same for both MR systems. SNR and CNR values of the stented part of the vessel phantom increased from 320 +/- 33 to 618 +/- 40 and from 306 +/- 34 to 596 +/- 40 at 3 T when compared with 1.5 T, resulting in a significant signal gain of 93% at the higher field strength. CONCLUSIONS: 3 Tesla MRA of aortic stent grafts in a phantom model demonstrates an increase in SNR and CNR when compared with 1.5 T. However, the magnitude of imaging artifacts as well as coherent intraluminal signal loss within the stent does not increase equally in both MR systems.