Magnetic resonance imaging of pulmonary parenchymal disease using a modified breath-hold 3D gradient-echo technique: initial observations

The Application and Value of 3T Magnetic Resonance Imaging in the Display of Pulmonary Nodules

Objective

The aim of this study was to evaluate the sensitivity and accuracy of multi-sequence 3T magnetic resonance imaging (MRI) in the detection of different types of pulmonary nodules.

Methods

A total of 68 patients with pulmonary nodules identified using computed tomography (CT) subsequently underwent MRI. Using CT images with a slice thickness of 1 mm as the gold standard, the sensitivity of three MRI sequences in detecting different types of pulmonary nodules was calculated, and the image quality was also evaluated. Nodule types included solid nodules, ground glass nodules (GGN), and part-solid nodules (PSN). Statistical analyses of data were conducted using the software SPSS 21.0. The intra-class correlation coefficient was calculated in order to compare the consistency of nodule size in both MRI and CT.

Results

CT detected 188 pulmonary nodules in 68 patients, including 87 solid nodules and 101 sub-solid nodules, the latter comprising 46 PSNs and 55 GGNs. The average nodule diameter was approximately 7.7 mm. The sensitivity of MRI in detecting nodules ≥ 6 mm in diameter and those of > 8 mm in diameter was 92% and 100%, respectively, and the sequence with the highest detection rate was T2-BLADE. In relation to solid nodules, the sequence with the highest detection rate was T1 Star-VIBE, while the T2-BLADE sequence demonstrated the highest detection rate of sub-solid nodules. The image quality of the T1 Star-VIBE sequence was better than that of both the T2-HASTE and the T2-BLADE sequences. The consistency of CT and MRI sequences for nodule size was high with a consistency coefficient of 0.94–0.98.

Conclusion

The detection rate of MRI for nodules with a diameter of > 8 mm was 100%. The T2-BLADE sequence had the highest detection sensitivity. The sequence with the best image quality was the T1 Star-VIBE.

Contrast-enhanced body magnetic resonance angiography: how we do it

This review introduces the basic principles of contrast-enhanced magnetic resonance (MR) angiography and details four contrast-enhanced MR angiography sequences for body imaging with extracellular gadolinium-based contrast agents in pediatric patients. Specifically, this review covers (1) respiratory-navigated, cardiac-gated MR angiography; (2) time-resolved MR angiography; (3) conventional MR angiography; and (4) modified spoiled gradient echo variants. We present and discuss indications, technical considerations, sequence optimization, advantages and disadvantages, along with practical tips and illustrative case examples for each sequence.

Thoracic MRI evaluation of sarcoidosis in children

BACKGROUND

Childhood sarcoidosis is a very rare granulomatous disorder with an unknown etiology. Stage 1 disease is the most common whereas stages 2, 3, and 0 are rare in children.

OBJECTIVE

To evaluate thoracic findings of pediatric pulmonary sarcoidosis on MRI and to compare them with CT findings.

METHODS

Between August 2010 and May 2015, seven consecutive pediatric patients (four male, three female; age range: 8-18 years, mean age: 13.5 ± 3.01 years) who were diagnosed with sarcoidosis were enrolled in our study prospectively. Inclusion criterion was patients with stages 1-4 sarcoidosis who underwent contrast enhanced chest CT for initial diagnosis or follow-up evaluation of thoracic findings and exclusion criteria were patients with stage 0 disease with extra-pulmonary manifestations (n = 4).

RESULTS

Two patients who recovered from stage 2 to stage 0 were interpreted as normal. Five patients had abnormal findings on chest CT, including hilar/mediastinal lymphadenopathy (n = 5, 71%), nodules larger than 3 mm (n = 4, 57%), ground glass opacity (n = 4, 57%), thickening of the pleura/fissure (n = 3, 42%), interlobular septal thickening (n = 2, 28%), atelectasis (n = 1, 14%), consolidation (n = 1, 14%), bronchiectasis (n = 1, 14%), intraparenchymal and subpleural cysts (n = 1,14%), fibrotic bands (n = 1, 14%), and enlarged pulmonary artery (n = 1, 14%). Findings that were detected on CT but not observed by lung MRI were nodules <3 mm (n = 4, 57%), mild bronchiectasis and mild ground glass opacity (n = 1, 14%), and subpleural and intraparenchymal cysts (n = 1, 14%). The sensitivity and specificity of MRI were 85.2% and 100%, respectively. There was no statistically significant difference between lung MRI and CT in detecting the thoracic findings in stages 1, 2, and 4 sarcoidosis (P = 0.1336, 95%Cl).

CONCLUSION

Contrast-enhanced lung MRI with fast imaging sequences is a highly sensitive imaging modality and comparable with CT in evaluating both lung and cardiac abnormalities in pediatric sarcoidosis. Given there is no associated ionizing radiation, chest MRI is a promising imaging modality in this pediatric patient population. Pediatr Pulmonol. 2017;52:494-499. © 2016 Wiley Periodicals, Inc.

Proton Magnetic Resonance Imaging for Initial Assessment of Isolated Mycobacterium avium Complex Pneumonia

RATIONALE

Computed tomographic (CT) radiography is the reference standard for imaging Mycobacterium avium complex (MAC) lung infection. Magnetic resonance imaging (MRI) has been shown to be comparable to CT for characterizing other pulmonary inflammatory conditions, but has not been rigorously tested for imaging MAC pneumonia.

OBJECTIVES

To determine the feasibility of pulmonary MRI for imaging MAC pneumonia and to assess the degree of agreement between MRI and CT for assessing the anatomic features and lobar extent of MAC lung infections.

METHODS

Twenty-five subjects with culture-confirmed MAC pneumonia and no identified coinfecting organisms were evaluated by thoracic MRI and then by chest CT imaging performed up to 1 week later. After deidentification, first the MRI and then the CT scans were scored 2 weeks apart by two chest radiologists working independently of one another. Discrepancies were resolved by a third chest radiologist. The scans were scored for bronchiectasis, consolidation or atelectasis, abscess or sacculation, nodules, and mucus plugging using a three-point lobar scale (absent, <50% of lobe, and >50% of lobe). Agreement analyses and ordinary least products regressions were performed.

MEASUREMENTS AND MAIN RESULTS

A fixed bias was found between total CT and MRI scores, with CT scoring higher on average (median difference: 4 on a scale of 48; interquartile range: 3, 6). Fixed biases were found for bronchiectasis and consolidation or atelectasis subscale scores. Both fixed and proportional biases were found between CT and MRI mucus plugging scores. No bias was found between CT and MRI nodule scores. There was nearly perfect lobar percent agreement for more conspicuous findings such as consolidation or atelectasis and abscess or sacculation.

CONCLUSIONS

In this exploratory study of 25 adult patients with culture-proven MAC lung infection, we found moderate agreement between MRI and CT for assessing the anatomic features and lobar extent of disease. Given the feasibility of chest MRI for this condition, future work is warranted to assess the clinical impact of MRI compared with CT in assessing progression of untreated MAC infection and response to treatment over time.

Diagnosing Lung Nodules on Oncologic MR/PET Imaging: Comparison of Fast T1-Weighted Sequences and Influence of Image Acquisition in Inspiration and Expiration Breath-Hold

Objective

First, to investigate the diagnostic performance of fast T1-weighted sequences for lung nodule evaluation in oncologic magnetic resonance (MR)/positron emission tomography (PET). Second, to evaluate the influence of image acquisition in inspiration and expiration breath-hold on diagnostic performance.

Materials and Methods

The study was approved by the local Institutional Review Board. PET/CT and MR/PET of 44 cancer patients were evaluated by 2 readers. PET/CT included lung computed tomography (CT) scans in inspiration and expiration (CTin, CTex). MR/PET included Dixon sequence for attenuation correction and fast T1-weighted volumetric interpolated breath-hold examination (VIBE) sequences (volume interpolated breath-hold examination acquired in inspiration [VIBEin], volume interpolated breath-hold examination acquired in expiration [VIBEex]). Diagnostic performance was analyzed for lesion-, lobe-, and size-dependence. Diagnostic confidence was evaluated (4-point Likert-scale; 1 = high). Jackknife alternative free-response receiver-operating characteristic (JAFROC) analysis was performed.

Results

Seventy-six pulmonary lesions were evaluated. Lesion-based detection rates were: CTex, 77.6%; VIBEin, 53.3%; VIBEex, 51.3%; and Dixon, 22.4%. Lobe-based detection rates were: CTex, 89.6%; VIBEin, 58.3%; VIBEex, 60.4%; and Dixon, 31.3%. In contrast to CT, inspiration versus expiration did not alter diagnostic performance in VIBE sequences. Diagnostic confidence was best for VIBEin and CTex and decreased in VIBEex and Dixon (1.2 ± 0.6; 1.2 ± 0.7; 1.5 ± 0.9; 1.7 ± 1.1, respectively). The JAFROC figure-of-merit of Dixon was significantly lower. All patients with malignant lesions were identified by CTex, VIBEin, and VIBEex, while 3 patients were false-negative in Dixon.

Conclusion

Fast T1-weighted VIBE sequences allow for identification of patients with malignant pulmonary lesions. The Dixon sequence is not recommended for lung nodule evaluation in oncologic MR/PET patients. In contrast to CT, inspiration versus expiratory breath-hold in VIBE sequences was less crucial for lung nodule evaluation but was important for diagnostic confidence.

(1)H-MR imaging of the lungs at 3.0 T

BACKGROUND

One disadvantage of magnetic resonance imaging (MRI) is the inability to adequately image the lungs. Recent advances in hyperpolarized gas technology [e.g., helium-3 ((3)He) and xenon-129 ((129)Xe)] have changed this. However, the required technology is expensive and often needing extra physics or engineering staff. Hence there is considerable interest in developing (1)H (proton)-based MRI approaches that can be readily implemented on standard clinical systems. Thus, the purpose of this work was to compare a newly developed free breathing proton-based MR lung imaging method to that of a standard gadolinium (Gd) based perfusion approach.

METHODS

Healthy volunteers [10] were scanned using a 3-T MRI with 8 parallel receivers, and a cardiac gated fast spin echo (FSE) sequence. Acquisition was cardiac triggered, with different time delays incremented to cover the entire cardiac cycle. Image k-space was filled rectilinearly. But to reduce motion artefacts k-space was retrospectively sorted using the minimal variance algorithm (MVA), based on physiologic data recorded from both the respiratory bellows and electrocardiogram (ECG). Resorted and reconstructed FSE images were compared to contrast enhanced lung images, obtained following intravenous injection of Gd-DTPA-BMA.

RESULTS

Biphasic variation in FSE lung signal intensity was observed across the cardiac cycle with a maximal signal change following rapid cardiac ejection (between S and T waves), and following rapid isovolumetric relaxation. A difference image between systolic and diastolic states in the cardiac cycle resulted in images with improved lung contrast to noise ratio (CNR). FSE image intensity was uniform over lung parenchyma while Gd-based enhancement of spoiled gradient recalled echo (SPGR) images showed gravitational dependence.

CONCLUSIONS

Here we show how 1H-MR images of lung can be obtained during free breathing. The image contrast obtained during this approach is likely the result of flow and oxygen modulation during the cardiac cycle. This free breathing method provides lung images comparable to those obtained using Gd-enhancement. Besides having the advantage of free breathing, this approach doesn't require any Gd-contrast or suffer from methodological problems associated with perfusion (e.g., poor bolus timing). However, as gravitational differences typically observed in lung perfusion are not visible with this method it is not providing exclusive microvascular perfusion information.

Fetal MRI: A Technical Update with Educational Aspirations

Fetal magnetic resonance imaging (MRI) examinations have become well-established procedures at many institutions and can serve as useful adjuncts to ultrasound (US) exams when diagnostic doubts remain after US. Due to fetal motion, however, fetal MRI exams are challenging and require the MR scanner to be used in a somewhat different mode than that employed for more routine clinical studies. Herein we review the techniques most commonly used, and those that are available, for fetal MRI with an emphasis on the physics of the techniques and how to deploy them to improve success rates for fetal MRI exams. By far the most common technique employed is single-shot T2-weighted imaging due to its excellent tissue contrast and relative immunity to fetal motion. Despite the significant challenges involved, however, many of the other techniques commonly employed in conventional neuro- and body MRI such as T1 and T2*-weighted imaging, diffusion and perfusion weighted imaging, as well as spectroscopic methods remain of interest for fetal MR applications. An effort to understand the strengths and limitations of these basic methods within the context of fetal MRI is made in order to optimize their use and facilitate implementation of technical improvements for the further development of fetal MR imaging, both in acquisition and post-processing strategies.

Bias atlases for segmentation-based PET attenuation correction using PET-CT and MR

This study was to obtain voxel-wise PET accuracy and precision using tissue-segmentation for attenuation correction. We applied multiple thresholds to the CTs of 23 patients to classify tissues. For six of the 23 patients, MR images were also acquired. The MR fat/in-phase ratio images were used for fat segmentation. Segmented tissue classes were used to create attenuation maps, which were used for attenuation correction in PET reconstruction. PET bias images were then computed using the PET reconstructed with the original CT as the reference. We registered the CTs for all the patients and transformed the corresponding bias images accordingly. We then obtained the mean and standard deviation bias atlas using all the registered bias images. Our CT-based study shows that four-class segmentation (air, lungs, fat, other tissues), which is available on most PET-MR scanners, yields 15.1%, 4.1%, 6.6%, and 12.9% RMSE bias in lungs, fat, non-fat soft-tissues, and bones, respectively. An accurate fat identification is achievable using fat/in-phase MR images. Furthermore, we have found that three-class segmentation (air, lungs, other tissues) yields less than 5% standard deviation of bias within the heart, liver, and kidneys. This implies that three-class segmentation can be sufficient to achieve small variation of bias for imaging these three organs. Finally, we have found that inter- and intra-patient lung density variations contribute almost equally to the overall standard deviation of bias within the lungs.

3 Tesla proton MRI for the diagnosis of pneumonia/lung infiltrates in neutropenic patients with acute myeloid leukemia: initial results in comparison to HRCT

PURPOSE

To evaluate the diagnostic accuracy of 3 Tesla proton MRI for the assessment of pneumonia/lung infiltrates in neutropenic patients with acute myeloid leukemia.

MATERIAL AND METHODS

In a prospective study, 3 Tesla MRI was performed in 19 febrile neutropenic patients (5 women, 14 men; mean age 61 years ± 14.2; range 23-77 years). All patients underwent high-resolution CT less than 24h prior to MRI. The MRI protocol (Magnetom Tim Trio, Siemens) included a T2-weighted HASTE sequence (TE/TR: 49 ms/∞, slice thickness 6mm) and a high-resolution 3D VIBE sequence with an ultra-short TE<1 ms (TE/TR 0.8/2.9 ms, slice thickness 2mm). The VIBE sequence was examined before and after intravenous injection of 0.1 mmol/kg gadoterate meglumine (Dotarem, Guerbet). The presence of pulmonary abnormalities, their location within the lung, and lesion type (nodules, consolidations, glass opacity areas) were analyzed by one reader and compared to the findings of HRCT, which was evaluated by a second independent radiologist who served as the reference standard. The findings were compared per lobe in each patient and rated as true positive (TP) findings if all three characteristics (presence, location, and lesion type) listed above were concordant to HRCT.

RESULTS

Pulmonary abnormalities were characterized by 3 Tesla MRI with a sensitivity of 82.3% and a specificity of 78.6%, resulting in an overall accuracy of 88% (NPV/PPV 66.7%/89.5%). In 51 lobes (19 of 19 patients), pulmonary abnormalities visualized by MR were judged to be concordant in their location and in the lesion type identified by both readers. In 22 lobes (11 of 19 patients), no abnormalities were present on either MR or HRCT (true negative). In 6 lobes (5 of 19 patients), ground glass opacity areas were detected on MRI but were not visible on HRCT (false positives). In 11 lobes (7 of 19 patients), MRI failed to detect ground glass opacity areas identified by HRCT. However, since the abnormalities were disseminated in these patients, accurate treatment decisions were possible in every case based on MRI. In one case MRI showed a central area of cavitation, which was not visualized by HRCT.

CONCLUSION

Infectious nodules and consolidations can be detected in neutropenic patients with acute myeloid leukemia with a sufficient diagnostic accuracy by 3 Tesla MRI. Detection of ground glass opacity areas is the main limitation of 3-Tesla MRI when compared to HRCT.

Whole-body MRI: comprehensive evaluation on a 48-channel 3T MRI system in less than 40 minutes. Preliminary results

OBJECTIVE: To evaluate a comprehensive MRI protocol that investigates for cancer, vascular disease, and degenerative/inflammatory disease from the head to the pelvis in less than 40 minutes on a new generation 48-channel 3T system. MATERIALS AND METHODS: All MR studies were performed on a 48-channel 3T MR scanner. A 20-channel head/neck coil, two 18-channel body arrays, and a 32-channel spine array were employed. A total of 4 healthy individuals were studied. The designed protocol included a combination of single-shot T2-weighted sequences, T1-weighted 3D gradient-echo pre- and post-gadolinium. All images were retrospectively evaluated by two radiologists independently for overall image quality. RESULTS: The image quality for cancer was rated as excellent in the liver, pancreas, kidneys, lungs, pelvic organs, and brain, and rated as fair in the colon and breast. For vascular diseases ratings were excellent in the aorta, major branch vessel origins, inferior vena cava, portal and hepatic veins, rated as good in pulmonary arteries, and as poor in the coronary arteries. For degenerative/inflammatory diseases ratings were excellent in the brain, liver and pancreas. The inter-observer agreement was excellent. CONCLUSION: A comprehensive and time efficient screening for important categories of disease processes may be achieved with high quality imaging in a new generation 48-channel 3T system.

Lung morphology assessment with balanced steady-state free precession MR imaging compared with CT

PURPOSE

To evaluate the utility of 1.5-T noncontrast magnetic resonance (MR) imaging of the lung parenchyma and to compare it with computed tomography (CT) in the assessment of interstitial lung disease and other morphologic lung abnormalities.

MATERIALS AND METHODS

Institutional review board approval was obtained for retrospective image analysis. A total of 236 patients who underwent MR imaging and CT as part of their assessment for suspected pulmonary hypertension were included in this study. Lung MR imaging was performed with a 1.5-T system as a stack of axial two-dimensional balanced steady-state free precession (bSSFP) acquisitions. Two radiologists independently evaluated CT and MR images for various morphologic abnormalities, such as pulmonary fibrosis, pleural and mediastinal disease, solid lesions, bronchial disease, and emphysema. Κ statistics were used to measure interobserver agreement.

RESULTS

Sensitivity and specificity of MR imaging in the identification of pulmonary fibrosis (n = 46) were 89% (95% confidence interval: 77%, 96%) and 91% (95% confidence interval: 76%, 98%), respectively, when compared with CT. In comparison to CT, MR imaging depicted 75% of ground-glass opacities. Nine of the 12 noncalcified nodules were identified on MR images. Lung nodules (75%, κ = 0.71) and effusions (100%, κ = 0.89) were also well visualized on MR images. MR imaging was however less effective in depicting emphysema (16%, κ = 0.60) and minor fibrosis (67%, κ = 0.79).

CONCLUSION

This study shows bSSFP MR imaging is inferior to CT in imaging parenchymal lung disease; however, this study does demonstrate for the first time a potential role for the bSSFP sequence as an alternative radiation-free noncontrast imaging modality for use in patients with pulmonary fibrosis.

Lung morphology assessment using MRI: a robust ultra-short TR/TE 2D steady state free precession sequence used in cystic fibrosis patients

To evaluate feasibility and diagnostic quality of ultra-short TR/TE two-dimensional (2D) steady state free precession (SSFP) MRI for cystic fibrosis (CF) patients. We performed lung MRI at 1.5 Tesla in 20 CF-patients (6-17 years, 12 males). Axial, coronal, and sagittal sections were acquired in inspiration and expiration with maximum breath-hold time 10 s. MR and CT images were scored using a modified Brody scoring system to assess bronchiectasis, mucous plugging, atelectasis/consolidations, and air trapping. All images were scored by two experienced observers. A complete MR investigation took maximally 15 min. Maximal breath-holds were only 10 s and well tolerated. MRI identified major bronchiectasis, mucous plugging and atelectasis. End-expiratory scans showed patches of parenchyma with reduced signal intensity that may corresponded to areas of trapped air on expiratory CT scans. This MRI protocol based on ultra-short TR/TE 2D SSFP is quick and well tolerated and provides highly relevant imaging features as seen on CT in CF patients. Most importantly, the SNR of the expiratory scans enables to visualize air trapping. The preliminary results of this study suggest MRI as a noteworthy additional imaging tool for routine monitoring of CF patients.

Pulmonary Infections – Pneumonia

The different appearances of pneumonia such as ill-defined nodules, ground-glass opacities, and consolidations can be easily detected and differentiated with MRI. Since very small nodules and calcifications are extremely challenging due to rather thick slices and loss of signal, MRI is highly recommended as a follow-up tool, to avoid repetitive investigations using ionizing radiation. With the sensitivity of T2-weighted sequences and the potential of contrast-enhanced T1-weighted sequences important differential diagnostic considerations can be provided. Additionally, developing complications, such as pericardial or pleural effusions, empyema or lung abscess, are easily recognized. Current and future studies are to demonstrate that MRI is well suited as a monitoring and follow-up tool during and after therapy and compares favorably with CT or other imaging methods regarding sensitivity and specificity.

When should abdominal magnetic resonance imaging be used?

When assessing the use of an imaging study, historically 2 criteria were used, diagnostic accuracy and cost of the study. However, as the awareness of risk for radiation-induced cancer in the general population increases as a direct result of more computed tomography (CT) studies being performed, reevaluation of the approach to imaging studies is necessary. The new imaging paradigm considers patient safety as an important aspect of assessing the role of an imaging modality. The primary goals of the new imaging paradigm should be diagnostic accuracy and patient safety, with the secondary goal being more affordable cost of study. In formulating a plan for when to use body magnetic resonance imaging (MRI), one has to consider all of these criteria and should also consider the question of when CT has unmatched diagnostic accuracy. The advantages of the spatial resolution of CT are mainly realized when there is great contrast between what is being looked for and background tissue; examples include small lung nodules and renal calculi. The greater intrinsic soft tissue contrast resolution and greater sensitivity for the presence or absence of intravenous contrast are appreciated in MRI studies, circumstances in which lesions occur within an organ without altering its exterior contour. This is well-shown for liver lesions. Adding patient safety into the equation, MRI should be indicated in exams in which there is no greater difference in diagnostic accuracy between CT and MRI, in patients with greater concern for radiation safety such as pediatric patients, and in cases of multiple or serial exams.

3.0-T MRI evaluation of patients with chronic liver diseases: initial observations

PURPOSE

To describe the use of 3.0-T magnetic resonance imaging (MRI) for the evaluation of chronic liver diseases.

MATERIALS AND METHODS

Two groups of patients who had chronic liver diseases and underwent 3.0-T MRI for evaluation of the liver were included in the study. The first group of patients included 66 consecutive patients (33 male, 33 female; mean age+/-standard deviation, 56+/-11). The second group of patients included 30 consecutive patients (18 males, 12 females; mean age+/-standard deviation, 53+/-10) in whom Variable-Rate Selective Excitation (VERSE) pulses and improved adjustments procedure were used during the acquisitions. Imaging findings of chronic liver diseases, predetermined artifacts and image quality of all individual sequences in the first group and predetermined artifacts and image quality of T2-weighted sequences in the second group were reviewed retrospectively and independently by two reviewers. chi-Square tests were used to compare the findings between two groups of patients and individual sequences. Kappa statistics were used to determine the extent of agreement between the reviewers.

RESULTS

Fifteen dysplastic nodules in 6 of 66 (9%) patients and 12 hepatocellular carcinomas in 11 of 66 (17%) patients were detected. Excluding motion artifacts, three-dimensional (3D) T1-weighted gradient-echo (GE) sequence was the least affected sequence by the artifacts. Image quality of T1-weighted 3D-GE sequences was excellent in 43 of 66 (65%) patients. In-phase and out-of-phase T1-weighted spoiled GE (SGE) images were fair in 62 of 66 (94%) and 61 of 66 (92%) patients, respectively. The image quality of short tau inversion recovery (STIR) and half-Fourier rapid acquisition with relaxation enhancement (RARE) sequences were fair in 31 of 66 (47%) and 53 of 66 (80%) patients. STIR and half-Fourier RARE sequences in the second group demonstrated significantly better image quality (P=.03 and P<.0001).

CONCLUSION

3.0-T MRI allows the acquisition of very high quality postgadolinium 3D-GE sequence, which permitted the detection and characterization of lesions in the setting of chronic liver diseases. The use of VERSE pulses and improved adjustments procedure improved the image quality of T2-weighted sequences. In-phase/out-of-phase SGE sequences are at present of fair quality.

Dynamic contrast enhancement patterns of solitary pulmonary nodules on 3D gradient-recalled echo MRI

OBJECTIVE

The purpose of this study was to determine whether contrast enhancement features on 3D volumetric gradient-recalled echoMR images allow differentiation of benign from malignant solitary pulmonary nodules.

MATERIALS AND METHODS

Forty patients with solitary pulmonary nodules (range of greatest diameter, 7-40 mm) detected on CT underwent unenhanced MRI and contrast-enhanced MRI performed in 10 consecutive dynamic 3D volumetric gradient-recalled echo sequences every 30 seconds. Contrast enhancement patterns (homogeneous, heterogeneous, rim, peripheral, and central) of the lesions were visually evaluated, and time-intensity curves of the lesions were drawn.

RESULTS

Twenty patients had benign lesions (nine, tuberculoma; one, aspergilloma; nine, round atelectasis; one, postinflammatory nodule). The other 20 patients had malignant lesions (18, primary lung cancer; two, metastasis). At visual analysis, all 20 malignant lesions displayed peripheral enhancement with progressive heterogeneous fill-in on the late images. All nine tuberculomas and the aspergilloma had rim enhancement, and all nine round atelectasis lesions and the postinflammatory nodule had early intense homogeneous enhancement. Regarding the time-intensity curves, all malignant lesions except one lung cancer lesion had early peak enhancement with rapid washout. All benign lesions displayed early increasing enhancement with an early plateau in the second minute after contrast administration (nine tuberculomas and one aspergilloma) or a late plateau in the fourth minute (nine round atelectasis lesions and one postinflammatory nodule).

CONCLUSION

Rim contrast enhancement is highly valuable in the diagnosis of tuberculoma. Time-intensity curve types can be taken into consideration for noninvasive differentiation of lung cancer, tuberculoma, and round atelectasis.

Lung MRI at 1.5 and 3 Tesla

OBJECTIVES

To compare the image quality and lesion contrast of lung MRI using 5 different pulse sequences at 1.5 T and 3 T.

MATERIALS AND METHODS

Lung MRI was performed at 1.5 T and 3 T using 5 pulse sequences which have been previously proposed for lung MRI: 3D volumetric interpolated breath-hold examination (VIBE), true fast imaging with steady-state precession (TrueFISP), half-Fourier single-shot turbo spin-echo (HASTE), short tau inversion recovery (STIR), T2-weighted turbo spin-echo (TSE). In addition to 4 healthy volunteers, 5 porcine lungs were examined in a dedicated chest phantom. Lung pathology (nodules and infiltrates) was simulated in the phantom by intrapulmonary and intrabronchial injections of agarose. CT was performed in the phantom for correlation. Image quality of the sequences was ranked in a side-by-side comparison by 3 blinded radiologists regarding the delineation of pulmonary and mediastinal anatomy, conspicuity of pulmonary nodules and infiltrates, and presence of artifacts. The contrast of nodules and infiltrates (CNODULES and CINFILTRATES) defined by the ratio of the signal intensities of the lesion and adjacent normal lung parenchyma was determined.

RESULTS

There were no relevant differences regarding the preference for the individual sequences between both field strengths. TSE was the preferred sequence for the visualization of the mediastinum at both field strengths. For the visualization of lung parenchyma the observers preferred TrueFISP in volunteers and TSE in the phantom studies. At both field strengths VIBE achieved the best rating for the depiction of nodules, whereas HASTE was rated best for the delineation of infiltrates. TrueFISP had the fewest artifacts in volunteers, whereas STIR showed the fewest artifacts in the phantom. For all but the TrueFISP sequence the lesion contrast increased from 1.5 T to 3 T. At both field strengths VIBE showed the highest CNODULES (6.6 and 7.1) and HASTE the highest CINFILTRATES (6.1 and 6.3).

CONCLUSION

The imaging characteristics of different pulse sequences used for lung MRI do not substantially differ between 1.5 T and 3 T. A higher lesion contrast can be expected at 3 T.

MRI of the lung: Value of different turbo spin-echo, single-shot turbo spin-echo, and 3D gradient-echo pulse sequences for the detection of pulmonary metastases

PURPOSE

To compare the value of different MRI sequences of the lung for the detection of pulmonary metastases.

MATERIALS AND METHODS

A total of 28 patients with 225 pulmonary metastases confirmed at multidetector-row computed tomography (MDCT) underwent MRI of the lung, including breathhold T2-weighted single-shot turbo spin-echo (half-Fourier single-shot turbo spin-echo [HASTE] and inversion recovery [IR]-HASTE) and conventional turbo spin-echo (TSE and short-tau inversion recovery [STIR]) sequences, a respiratory- and pulse-triggered black-blood STIR sequence (triggered STIR), and breathhold pre- and postcontrast volumetric interpolated 3D gradient-echo (VIBE) sequences. MR images were reviewed by three independent observers and results were correlated with MDCT, which served as standard of reference. Lesion-to-lung contrast-to-noise ratios (CNRs) and image artifacts were also assessed.

RESULTS

CNRs were highest on TSE images (P < 0.001). Mean sensitivities for lesion detection with triggered STIR, TSE, and STIR were 72.0%, 69.0%, and 63.4%, respectively. With HASTE, IR-HASTE, and pre- and postcontrast VIBE, significantly lower sensitivities were obtained (P < 0.05), although artifacts due to physiological motion were less distinct with these sequences compared to TSE and STIR (P < 0.05).

CONCLUSION

Conventional TSE sequences are more sensitive in depicting pulmonary metastases than single-shot TSE or 3D gradient-echo sequences. Respiratory and pulse triggering can improve lesion detection, but increases acquisition time substantially.

Emerging techniques: Whole-body screening and staging with MRI

Strategies for screening or tumor staging include various modalities such as plain radiography, computed tomography (CT), MRI, and ultrasound. Technical innovations have created the feasibility to use MRI to image the entire body in a relatively short time-period. Whole-body MRI may play a potentially important role in evaluating for cancer or vascular disease. This article describes the rationale for using MRI to display the entire body, the techniques employed in whole-body MRI, possibilities and limitations, and summarizes first clinical results for screening and staging purposes.

Detection of Pulmonary Nodules Using a 2D HASTE MR Sequence: Comparison with MDCT

OBJECTIVE

The objective of our study was to determine the diagnostic performance of MRI based on a HASTE sequence for the detection of pulmonary nodules in comparison with MDCT.

MATERIALS AND METHODS

Thirty patients with known pulmonary nodules underwent both MRI and CT. CT of the lung served as the standard of reference and was performed on a 4-MDCT scanner using a routine protocol. MRI was performed with axial and coronal HASTE sequences using a high-performance 1.5-T MR scanner. Image data were analyzed in three steps after completion of all data acquisition. Step 1 was the analysis of all the CT image data. Step 2 was the analysis of all the MR image data while blinded to the results of the CT findings. Step 3 closed with a simultaneous review of all corresponding CT and MRI data, including a one-to-one correlation of the size and location of all the nodules that were detected.

RESULTS

Compared with the sensitivity of CT, the sensitivity values for the HASTE MR sequence were as follows: 73% for lesions less than 3 mm, 86.3% for lesions between 3 and 5 mm, 95.7% for lesions between 6 and 10 mm, and 100% for lesions larger than 10 mm. The overall sensitivity of the HASTE sequence for the detection of all pulmonary lesions was 85.4%.

CONCLUSION

An MRI examination that consists of a HASTE sequence allows one to detect, exclude, or monitor pulmonary lesions that are 5 mm and bigger. Suspicious lesions smaller than 5 mm still need to be validated using CT.

Dynamic magnetic resonance imaging of solitary pulmonary nodules: utility of kinetic patterns in differential diagnosis

OBJECTIVE

The aim of this study was to evaluate the clinical feasibility of dynamic magnetic resonance (MR) imaging with a 3-dimensional (3D) gradient recalled echo (GRE) volumetric interpolated breath-hold examination (VIBE) sequence to differentiate between benign and malignant solitary pulmonary nodules (SPNs).

METHODS

Dynamic 3D GRE VIBE was performed in 45 patients with SPNs. For each lesion, the morphologic parameters, including the edge configuration, presence of peripheral enhancement (PE), and an internal signal on T2-weighted images, and the kinetic enhancement parameters were evaluated.

RESULTS

All 29 of the malignant SPNs had internal enhancement, whereas 13 (81%) of the benign SPNs did not exhibit internal enhancement. A washout pattern was only observed in the malignant SPNs. The presence of PE was found in 56% of the benign SPNs and in 50% of the malignant SPNs. The lesion size was significantly different between malignant SPNs with PE and those without PE (P <0.01). The positive predictive value for malignancy was 91% (29 of 32 malignant SPNs). The negative predictive value was 100% (13 of 13 benign SPNs).

CONCLUSIONS

A combination of morphologic criteria and kinetic information is useful for differentiating between benign and malignant SPNs. In particular, internal enhancement with PE and positive visual washout is thought be a useful tool.

Fast T1- and T2-weighted pulmonary MR-imaging in patients with bronchial carcinoma

PURPOSE

A prospective study to evaluate the diagnostic potential and limitations of three fast MRI sequences in patients with bronchial carcinoma based on the comparison with spiral CT.

MATERIAL AND METHODS

Three fast chest MRI sequences from 20 patients with central or peripheral bronchial carcinoma were evaluated by two observers for relation of tumour to adjacent structures, lymph node enlargement, additional pulmonary lesions and artefacts. The information from MR-imaging was compared with the results from spiral CT. MRI comprised a T1-3D-GRE breath-hold examination ("VIBE", TR/TE 4.5/1.9 ms, flip-angle 12 degrees , matrix 502 x 512, 2.5 mm coronal slices), a breath-hold, T2-HASTE sequence (TR/TE 2000/43 ms, matrix 192 x 256, 10 mm coronal slices) and a respiration-triggered T2-TSE sequence (TR/TE 3000-6000/120 ms, matrix 270 x 512, 6 mm transverse slices). The FOV was adapted individually (380-480 mm).

RESULTS

The presence of the primary bronchial carcinoma and infiltration of thoracic structures by tumour tissue could be demonstrated by all sequences. VIBE sequence was more suitable for detecting small pulmonary nodules than the other MRI examinations, but compared to CT still 20% of these lesions were missed. Contrary to VIBE and T2-weighted TSE scans, HASTE sequence was limited in imaging mediastinal lymph nodes due to missing relevant findings in 2/20 patients. HASTE images significantly provided the lowest rate of artefacts in imaging lung parenchyma (P < 0.001 in peripheral parenchyma), but spatial resolution was limited in this sequence. Concerning the differentiation between tumour and adjacent atelectasis (n = 8), T2-weighted TSE imaging was superior to CT and VIBE in all cases and to HASTE sequence in 4/8 patients.

CONCLUSION

The combination of VIBE and HASTE sequence allows for an adaequate imaging of thoracic processes in patients with bronchial carcinoma, limited only in visualizing small pulmonary nodules. To obtain more detail resolution and to differentiate tumour tissue from adjacent atelectasis, T2-TSE examination may be added in selected cases.

Whole-body magnetic resonance imaging

Whole-body magnetic resonance imaging is a fast and accurate modality for the detection of disease throughout the entire body. Technical improvements including the availability of different high image quality MR sequences, the remote movement of the imaging table, and the use of specialized surface coils have rendered whole-body screening with MRI a feasible method. In this article we describe underlying techniques and report on first clinical experiences of whole-body magnetic resonance imaging as a staging and screening method. Furthermore, advantages and limitations compared with whole-body imaging based on computed tomography are discussed.

Lung MRI at 3.0 T: a comparison of helical CT and high-field MRI in the detection of diffuse lung disease

The purpose of this study was to evaluate the feasibility of high-field magnetic resonance imaging (MRI) of the lung using a T2-weighted fast-spin echo (TSE) sequence. Comparison was made with helical computed tomography CT findings in patients with diffuse pulmonary diseases. Prospective segment-wise analysis of high-field MR imaging findings in 15 patients with diffuse pulmonary diseases was made using helical CT and HRCT as the standard of reference. The MR studies were performed on a 3.0-T whole body system (Intera 3T, Philips Medical Systems) using a T2w TSE sequence with respiratory and cardiac gating (TE 80 ms TR 1,500-2,500 ms; turbo factor 17; 22 slices with 7/2-mm slice thickness and gap; 256x192 matrix). MR artifacts were graded on a three-point scale (low, moderate, high). Lung MR studies were prospectively analyzed segment-by-segment and diagnosed as healthy or pathological; results were compared with helical CT findings. In all 15 patients, MR imaging of the lung was successful. All 15 MR studies were compromised by artifacts; however, the severity of these artifacts was classified as low or moderate in 8/15, respectively, 7/15 cases. A total of 143/285 lung segments showed diffuse lung disease in helical CT. With MRI, 133 of these 143 segments (93%) were judged to be diseased. The ten segments that received false negative MR diagnoses displayed non-acute pulmonary lesions with inherently low proton density (scars, granulomas). MRI at 3.0 T can detect diffuse pulmonary disease with a high sensitivity. Based on this experience, further pulmonary studies with high-field systems appear justified and promising.

Volumetric interpolated contrast-enhanced MRA for the diagnosis of pulmonary embolism in an ex vivo system

PURPOSE

To implement a three-dimensional gradient-recalled echo (GRE) volumetric interpolated breath-hold examination (VIBE) sequence for pulmonary contrast-enhanced MRA (CE-MRA) in an experimental setup.

MATERIALS AND METHODS

Eight porcine lungs were intubated, inflated inside a chest phantom, and examined at 1.5 T during slow perfusion (2-300 mL/minute). Three-dimensional-MRA was performed with and without contrast agent using three-dimensional-GRE (VIBE) with TR/TE = 4.5/1.9 msec, TA = 23 seconds, FOV = 390 mm, FA = 12 degrees /30 degrees, as well as a standard three-dimensional-GRE sequence and T2 fast spin-echo (FSE) sequences. Four of the eight lungs were embolized with autologous blood clots. By consensus readings, two observers evaluated the detectability of peripheral vessels, signal intensity over vessels and lung, and visualization of emboli. Digital subtraction angiograms served as a control to document vessel patency.

RESULTS

Prior to contrast administration, three-dimensional-VIBE/12 degrees yielded the best results for lung parenchyma signal and visualization of small vessels (third-order, P < 0.01); however, no emboli were detected (due to lack of contrast). After administration of contrast agent, three-dimensional-GRE (VIBE) at FA = 30 degrees provided significantly better results (fifth-order branches, documentation of subsegmental occlusions [fourth order], P < 0.01). T2-FSE images documented water uptake into the lungs. Digitally subtracted angiography (DSA) confirmed the patency of seventh-order branches.

CONCLUSION

This ex vivo study confirms the potential advantages of using a dual MR investigation for pulmonary embolism, combining three-dimensional-GRE (VIBE) at FA = 12 degrees to image lung parenchyma and at FA = 30 degrees for CE-MRA..

MR imaging of the chest using a contrast-enhanced breath-hold modified three-dimensional gradient-echo technique: comparison with two-dimensional gradient-echo technique and multidetector CT

OBJECTIVE

The purpose of this study was to assess the feasibility of performing MR imaging of the chest using a fat-suppressed gadolinium-enhanced modified three-dimensional (3D) gradient-echo technique with a volumetric interpolated breath-hold (VIB) sequence compared with using a standard two-dimensional (2D) breath-hold gradient-echo technique. MR images obtained using both techniques were compared with multidetector CT (MDCT) scans.

SUBJECTS AND METHODS

Paired gadolinium-enhanced 2D gradient-echo and 3D gradient-echo VIB images were acquired in 15 consecutive patients with suspected intrathoracic abnormalities. MDCT scans were available for comparison in 12 patients. Two reviewers independently analyzed the MR images obtained using the two techniques for overall quality, the degree of artifacts, and visibility of mediastinal or parenchymal abnormalities. The detectability of lesions on the 3D gradient-echo VIB images and 2D gradient-echo images was compared with the detectability of lesions on CT scans obtained in nine patients.

RESULTS

In all cases, the MR images obtained using the 3D gradient-echo technique with the VIB sequence were rated superior to those obtained using the 2D gradient-echo technique for quality, depiction of mediastinal structures, and clarity of pulmonary vessels and central airways. On the 3D gradient-echo VIB images, the degree of phase artifacts was lower (p < 0.001), but the degree of pixel graininess was higher (p < 0.05). Detectability, confidence and conspicuity levels, and marginal delineation of the pulmonary lesions were rated higher statistically on the 3D gradient-echo VIB images than on the 2D gradient-echo images. Of the 31 solid pulmonary abnormalities depicted on MDCT, 27 (87.1%) were detected on the 3D gradient-echo VIB images, and 21 (67.7%) were seen on the 2D gradient-echo images (p < 0.05). The 3D gradient-echo VIB images showed all 14 mediastinal lesions (100%) seen on MDCT, whereas the 2D gradient-echo images showed 12 (85.7%) of the 14 lesions (p > or = 0.05).

CONCLUSION

The gadolinium-enhanced modified 3D gradient-echo technique with the VIB sequence provides MR images that are superior in quality, have significantly fewer artifacts, and have a higher sensitivity for the detection of intrathoracic lesions compared with images obtained using the standard 2D gradient-echo technique.