Myocardial viability: rapid assessment with delayed contrast-enhanced MR imaging with three-dimensional inversion-recovery prepared pulse sequence

Contrast-enhanced magnetic resonance (MR) imaging allows detection of nonviable myocardium. The authors compared a one-breath-hold three-dimensional inversion-recovery gradient-echo MR sequence with a multiple-breath-hold two-dimensional inversion-recovery gradient-echo MR sequence for the detection of nonviable myocardium. On the basis of a quantitative and qualitative approach, total myocardial area and contrast material-enhanced area, as well as the presence and spatial extent of hyperenhancement, were analyzed separately for each MR image obtained with each sequence in 10 patients with chronic ischemic heart disease. Findings for total myocardial area and contrast-enhanced area agreed well between the two sequences. A high level of agreement was also found for the presence of hyperenhancement (kappa = 0.84), while agreement was poor for the transmural extent of hyperenhancement (kappa = 0.32), which was attributed to the blurred appearance of the three-dimensional MR images. Findings with the one-breath-hold three-dimensional MR sequence allow assessment of nonviable myocardium with good agreement with those with the multiple-breath-hold two-dimensional MR sequence.     

Suppression of cerebrospinal fluid and blood flow artifacts in FLAIR MR imaging with a single-slab three-dimensional pulse sequence: initial experience

The authors compared high-signal-intensity flow-related artifacts present with a conventional two-dimensional (2D) fluid-attenuated inversion recovery (FLAIR) sequence with those seen with a single-slab, three-dimensional (3D) FLAIR sequence. Four readers graded the subarachnoid space and intraventricular artifacts, the pulsation artifacts, and the conspicuity of cranial nerves in the posterior fossa. For all comparisons, differences between 2D and 3D images were highly statistically significant, with 3D imaging being superior in all cases.     

Detection of hepatic metastases: analysis of pulse sequence performance in MR imaging

Forty-three patients with liver metastases were imaged using 14 different pulse sequences (average, 7.5 sequences per patient) to allow direct comparison of their performance. "T2-weighted" spin-echo (SE) images, "T1-weighted" inversion recovery (IR) images, and "T1-weighted" SE images were obtained using a wide range of timing parameters. Pulse sequence performance was quantitated by measuring liver signal-to-noise (S/N) ratios and cancer-liver signal difference-to-noise (SD/N) ratios. Data were standardized to reflect a constant imaging time of 9 minutes for all pulse sequences. The SE 2,000/120 (TR [repetition time]/TE [echo time]) sequence resulted in the greatest SD/N ratio of the T2-weighted SE sequences but also yielded the low S/N ratios, poor anatomic resolution, and motion artifacts common to all T2-weighted SE images. IR sequence images were also sensitive to motion artifacts because of the use of a long TR (1,500 msec). Short TR/TE T1-weighted SE sequences (SE 260/18) had the greatest SD/N ratio (P less than .05), S/N ratio, and anatomic resolution. Furthermore, extensive signal averaging appears to be a powerful solution to all types of motion artifacts in the abdomen.     

Fast fluid-attenuated inversion-recovery imaging: first experience with a 3D version in epilepsy

We developed a 3D version of fast fluid-attenuated inversion-recovery imaging (FLAIR) which provides images with a slice thickness of 1.5 mm. We present our initial experience with 3D fast FLAIR in patients with epilepsy. We compared 3D fast FLAIR (slice thickness 1.5 mm), 2D fast FLAIR (slice thickness 5 mm) and a 3D spoiled GRASS (IRSPGR) sequence (slice thickness 1.5 mm) in 10 patients with lesional epilepsy (head injury 1, hippocampal sclerosis 2, low-grade glioma 2, dysembryoplastic neuroepithelial tumour 2, polymicrogyria 1, perinatal infarct 1 and presumed thrombosed aneurysm 1). Both 2D and 3D fast FLAIR sequences yielded higher conspicuity for lesions than the T1-weighted IRSPGR sequence, except in the patient with polymicrogyria. The extent of the lesion, in particular that of low-grade tumours, was best assessed on 3D fast FLAIR images. 3D fast FLAIR may be a useful additional tool especially for imaging low-grade tumours. Received: 22 October 1997 Accepted: 16 December 1997     

Diffusion tensor imaging in hydrocephalus: initial experience

PURPOSE AND BACKGROUND: Diffusion tensor imaging (DTI) is an MR imaging-based technique that provides an in vivo tool for visualization of white matter tracts. In this preliminary study, we used this technique to investigate the diffusion characteristics of white matter tracts in patients with hydrocephalus before and after surgery and compared them with age-matched volunteers. MATERIALS AND METHODS: Seven patients with different types of acute hydrocephalus (defined by acute clinical signs of increased intracranial pressure and imaging evidence of enlarged ventricles) underwent MR imaging including a DTI protocol before and after surgery for shunt placement/revision or ventriculostomy. Eight age-matched healthy subjects served as a control group. The DTI was acquired in a clinical setting that included 6 gradient directions with a b value of 1000 s/mm(2). RESULTS: Before surgery, in fiber systems lateral to the ventricles (corona radiata), the diffusion parallel to the fibers was increased (+10%) and the diffusion perpendicular to the fibers was decreased (-25%) in all patients, resulting in an overall increase in the fractional diffusion anisotropy (FA, +28%). Following surgery, the FA values approached those of control values in all except 1 patient. In the corpus callosum, the presurgery FA values in patients with hydrocephalus (HCP) were lower than those of control values, and no significant changes were seen following surgery. CONCLUSIONS: DTI can distinguish the compression characteristics of white matter before and after surgery in patients with HCP. At the acute stage of the disease, DTI characteristics point to white matter compression as a possible cause of the observed changes.     

Dual-source CT cardiac imaging: initial experience

The relation of heart rate and image quality in the depiction of coronary arteries, heart valves and myocardium was assessed on a dual-source computed tomography system (DSCT). Coronary CT angiography was performed on a DSCT (Somatom Definition, Siemens) with high concentration contrast media (Iopromide, Ultravist 370, Schering) in 24 patients with heart rates between 44 and 92 beats per minute. Images were reconstructed over the whole cardiac cycle in 10% steps. Two readers independently assessed the image quality with regard to the diagnostic evaluation of right and left coronary artery, heart valves and left ventricular myocardium for the assessment of vessel wall changes, coronary stenoses, valve morphology and function and ventricular function on a three point grading scale. The image quality ratings at the optimal reconstruction interval were 1.24±0.42 for the right and 1.09±0.27 for the left coronary artery. A reconstruction of diagnostic systolic and diastolic images is possible for a wide range of heart rates, allowing also a functional evaluation of valves and myocardium. Dual-source CT offers very robust diagnostic image quality in a wide range of heart rates. The high temporal resolution now also makes a functional evaluation of the heart valves and myocardium possible.     

Use of fluid-attenuated inversion-recovery pulse sequences for imaging the spinal cord.

Fourteen patients with disease of the spinal cord were imaged with fluid-attenuated inversion-recovery (FLAIR) sequences in which the inversion time was chosen to substantially reduce or null the signal from CSF. Lesions were seen with greater conspicuity than with conventional contrast-enhanced and -unenhanced T1- and T2-weighted sequences in 11 cases.     

Diffusion-weighted imaging of the spine with a non-carr-purcell-meiboom-gill single-shot fast spin-echo sequence: initial experience

BACKGROUND AND PURPOSE: To prospectively evaluate the signal-to-noise ratio (SNR) improvement in diffusion-weighted imaging (DWI) of the spine with the use of a newly developed non-Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo (SS-FSE) sequence and its effect on apparent diffusion coefficient (ADC) measurements. MATERIALS AND METHODS: Twenty-four patients were enrolled after written informed consent. DWI of the spine was obtained with an echo-planar imaging (EPI)-based sequence followed by a non-CPMG SS-FSE technique. SNR and ADC values were measured over a lesion-free vertebral corpus. A quality score was assigned for each set of images to assess the image quality. When a spinal lesion was present, contrast-to-noise ratio (CNR) and ADC were also measured. Student t tests were used for statistical analysis. RESULTS: Mean SNR values were 5.83 +/- 2.2 and 11.68 +/- 2.87 for EPI and non-CPMG SS-FSE DWI, respectively. SNR values measured in DWI using parallel imaging were found to be significantly higher (P < .01). Mean ADCs of the spine were 0.53 +/- 0.15 and 0.35 +/- 0.15 x 10(-3) mm(2)/s for EPI and non-CPMG SS-FSE DWI, respectively. Quality scores were found to be higher for the non-CPMG SS-FSE DWI technique (P < .05). Overall lesion CNR was found to be higher in DWI with non-CPMG SS-FSE. CONCLUSION: The non-CPMG SS-FSE technique provides a significant improvement to current EPI-based DWI of the spine. A study including a larger number of patients is required to determine the use of this DWI sequence as a supplementary tool to conventional MR imaging for increasing diagnostic confidence in spinal pathologic conditions.     

In-plane vascular imaging: pulse sequence design and strategy

Magnetic resonance (MR) angiography is a noninvasive method of obtaining images without contrast agents. Recent developments in sequence design have allowed images of moving spins to be obtained without a loss of signal by rephasing the spins with three or four gradient pulses to compensate for constant velocity or acceleration, respectively. At longer echo times (TE), this approach allowed for low readout gradients and high signal-to-noise ratios. Angiograms with a resolution of 300 micron were obtained. With additional sequences that allow some dephasing but minimal signal loss, separate images of arteries and veins were obtained. Phase information was used to estimate flow velocity. Application of the rephasing scheme to gradient-echo sequences allowed for ungated, fast MR angiograms. Acceleration correction was important for long TE sequences, but velocity-corrected, gradient-echo sequences with a very short TE were comparable to velocity- and acceleration-corrected, gradient-echo sequences with slightly longer TEs. With ungated three-dimensional, gradient-echo sequences, susceptibility artifacts were minimized and excellent contrast-to-noise ratios were obtained.     

The fluid-attenuated inversion-recovery pulse sequence in assessment of central nervous system involvement in myotonic dystrophy

We compared the fluid-attenuated inversion recovery (FLAIR) sequence with conventional spin-echo (SE) imaging for detection of involvement of the central nervous system in five patients with myotonic dystrophy (MD). The diagnosis was made based on clinical features and DNA analysis. All patients showed abnormal high-intensity lesions in the white matter on T2-weighted images, although these were more clearly visible using FLAIR. Received: 3 January 1997 Accepted: 18 June 1997     

Endorectal surface coil MR imaging of prostatic carcinoma with the inversion-recovery sequence

The value of inversion-recovery (IR) sequences in the diagnosis and staging of prostatic carcinoma with magnetic resonance (MR) imaging was studied. Twenty-six patients with carcinoma of the prostate were imaged at 1.5 T with an endorectal surface coil and with a variety of IR sequences and a set of spin-echo (SE) sequences for comparison. Ex vivo prostate specimens were imaged again at the same field strength. The two images were correlated with histologic sections. Cancer was identified with MR imaging in 96% of patients. Of the tumors more than 4 mm in diameter, 87% were identified on T2-weighted SE images, whereas only 26% were identified on IR images. However, IR images may be more useful in local staging of carcinoma. Gross capsular infiltration was present in only two patients; however, it was detectable (and excluded in five other patients) by means of IR images. It was not detectable on SE images. The high quality of images obtained with the endorectal coil was confirmed. The authors conclude that addition of the IR sequence to MR imaging with the endorectal coil may improve the usefulness of this examination.     

Three-tesla imaging of the knee: initial experience

Purpose To assess 3-T imaging of the knee.Materials and methods We reviewed 357 3-T magnetic resonance images of the knee obtained using a dedicated knee coil. From 58 patients who had arthroscopy we determined the sensitivity and specificity for anterior cruciate ligament (ACL) tear and medial and lateral meniscal tear.Results A chemical shift artifact showed prominently at 3 T even after improvements had been made by increasing the bandwidth. For complete ACL tear the sensitivity was 100% (95% confidence interval, CI, 75.30–100.00), and the specificity was 97.9% (95% CI 87.7–99.9). For the medial meniscus the sensitivity was 100.00% (95% CI 90.0–100.00), and the specificity was 83.3%(95% CI 66.6–95.3). For the lateral meniscus the sensitivity was 66.7% (95% CI 38.4–88.2), and the specificity was 97.6% (95% CI 87.1–99.9).Conclusions In general 3-T imaging allows a favorable display of anatomy and pathology. The lateral meniscus was assessed to be weaker than the other anatomic structures. Three-tesla imaging allows increased signal-to-noise ratio, increased resolution, and faster scanning times.     

Inversion-recovery-prepared dixon bSSFP: initial clinical experience with a novel pulse sequence for renal MRA within a breathhold

Purpose:

To evaluate the capability of a new breathhold non–contrast‐enhanced MRA method (Non‐contrast Outer Radial Inner Square k‐space Scheme, NORISKS) to visualize renal arteries by comparing the method with a routine clinical but significantly longer non–contrast‐enhanced (non‐CE) MRA technique.

Materials and Methods:

Eighteen subjects referred for abdominal MRI were examined with NORISKS and a routine non–contrast‐enhanced MRA technique. Two versions of NORISKS were evaluated: with and without ECG gating. The images were then scored independently and in blinded manner by two radiologists on 5‐point scales for visualization of the proximal and distal renal arteries and quality of fat suppression.

Results:

No statistically significant difference was detected between NORISKS and routine clinical non‐CE MRA in all categories except for visualization of the distal renal arteries where ungated NORISKS performed poorer than the routine non‐CE MRA (P < 10^?4).

Conclusion:

We have demonstrated a promising non‐CE MRA method for acquiring renal angiograms within a breathhold without any compromise in spatial resolution or coverage. ECG‐gated NORISKS is able to acquire renal angiograms that are comparable to a routine clinical non‐CE MRA method (Inhance IFIR, GE Healthcare), which requires approximately seven times the scan time of NORISKS. J. Magn. Reson. Imaging 2012;35:875–881. © 2011 Wiley Periodicals, Inc.

     

Superparamagnetic iron oxide-enhanced MR imaging: pulse sequence optimization for detection of liver cancer

The effects of magnetic resonance (MR) pulse sequences and timing parameters on tumor-liver contrast were studied in an animal model of metastatic liver cancer. Six spin-echo (SE), three inversion-recovery (IR), and four gradient-echo (GRE) sequences were evaluated at 0.6 T before and after injection of super-paramagnetic iron oxide. GRE techniques, irrespective of echo time and flip angle, showed the greatest change in signal intensity (enhancement) of the liver after administration of iron oxide. Single-acquisition GRE sequences (16 seconds) matched the contrast-to-noise ratio (C/N) performance of the most effective 6.4-minute SE sequences. Multiexcitation GRE sequences showed tumor-liver C/Ns per unit time that were significantly (P less than .05) higher than those achieved with SE and IR sequences. GRE sequences, which recruit intravoxel dephasing as an additional source of transverse relaxation enhancement (T2*), show a higher C/N per unit time and in this respect seem superior to SE and IR sequences for MR imaging with superparamagnetic iron oxide.     

MR imaging in patients with nipple discharge: initial experience

PURPOSE: To investigate the potential of magnetic resonance (MR) imaging in patients with nipple discharge. MATERIALS AND METHODS: Between February 1992 and December 1998, 23 patients with nipple discharge underwent contrast material-enhanced MR imaging at 1.5 T. Mammographic findings were negative in 22 of 23 patients and revealed asymmetry in one patient. Galactography was attempted in two patients, with negative findings in one patient and no success in the other. Fifteen of 23 patients underwent excisional biopsy-seven of 15 with MR imaging-guided localization, and one of 15 with mammographic localization. Eight of 23 patients were followed up clinically (range, 7-24 months; mean, 20 months). RESULTS: In 11 of the 15 (73%) patients who underwent excisional biopsy, MR imaging findings correlated with histopathologic findings. MR imaging demonstrated four of six benign papillomas and one of two fibroadenomas as circumscribed, enhancing subareolar masses. Findings of one MR imaging examination were negative, and benign tissue was found at excisional biopsy. MR imaging findings were suspicious in six of the seven patients with excisional biopsy findings of malignancy (regional enhancement [n = 2], ductal enhancement [n = 2], peripherally enhancing mass [n = 1], and spiculated mass [n = 1]). In one of the seven patients, a benign-appearing intraductal mass was identified at MR imaging; excisional biopsy revealed a benign papilloma with an adjacent focus of DCIS. CONCLUSION: MR imaging can help identify both benign and malignant causes of nipple discharge. It potentially offers a noninvasive alternative to galactography.     

双源CT冠状动脉成像的初步研究

目的初步探讨无需口服控制心率药物准备的双源CT冠状动脉成像的扫描技术和图像质量。方法对215例临床怀疑冠心病或冠状动脉早期病变患者进行无需口服控制心率药物准备的双源CT冠状动脉成像。扫描步骤包括平扫和增强扫描。用平扫图像行冠状动脉钙化积分，用增强扫描图像行多平面重组（MPR）、最大密度投影（MIP）及容积再现技术（VRT）重组。总结双源CT冠状动脉成像的扫描技术和后处理方法。将图像质量分为3级，按冠状动脉分段标准评价各个节段的图像质量。结果215例患者钙化积分值中位数为82．2（2．3～1827．9）。增强扫描平均心率为（80．6±15．3）（57～139）次／min，尽可能使冠状动脉良好显示的后处理方法有：（1）多个时相筛选法；（2）2个或多个时相补充法；（3）早搏去除法和心律不齐移位法。共评价3026个冠状动脉节段，其中图像质量为1级者占97．5％（2951／3026），2级者占2．0％（62／3026），为3级者占0．5％（13／3026）；图像质量为2级和3级的节段多由于呼吸伪影所致。215例患者共91例冠状动脉各节段均未见斑块或狭窄，共诊断〈50％冠状动脉狭窄节段112个，≥50％冠状动脉狭窄节段213个。结论双源CT冠状动脉成像在无需口服控制心率药物准备的情况下可获得非常好的冠状动脉各节段图像，心率不再是影响图像质量的关键因素，通过单时相或多时相重组可良好显示冠状动脉主干及分支。     

Magnetic resonance imaging of renal transplants: initial experience

Magnetic resonance imaging (MRI) was used in 45 renal transplant investigations (38 patients) using a Picker 0.15 T resistive system and a localized surface coil. An attempt was made to define optimal sequences in the evaluation of both normal and pathological transplants. Three sequences were found to be of value; a T1 weighted sequence (IR2180/700/40) to assess corticomedullary differentiation and its loss in acute rejection and acute tubular necrosis, a T2 weighted sequence (SE2000/80) for assessment of renal vessels and disturbances in blood supply, and a STIR (short tau inversion recovery) sequence (IR800/100/40) to define further the distended collecting system in obstruction and the presence of any perirenal collection. Encouraging results have been obtained, particularly in cases of acute rejection. It is suggested that the MRI scan is a useful screening test in cases of clinical doubt and may even obviate biopsy in some cases.     

Magnetic resonance imaging of laser phototherapy: initial experience

Interventional magnetic resonance imaging (MRI) is a newly established field, made possible by improvements in imaging times and the development of nonferromagnetic materials. Interstitial laser therapy (ILT) is a promising new technology in which laser energy is adininistered percutaneously via optical fibers. In this study, MRI was used to image acute experimental lesions induced nv ILT. Nine experimental lesions were induced in the musculature of an adult swine using an argon laser,' with output power of 1–4 watts, and exposure times of 10–40 s. T2-weighted images were obtained immediately after laser energy administration. The animal was then sacrificed and lesions were dissected and examined histologically. On MRI, target like lesions were seen with a high intensity center surrounded by two alternating concentric rings of low and high intensity. Histologically, concentric zones of tissue disruption were present. A center cavity was surrounded by a zone of coagulative necrosis, followed by a zone of vascuolated tissue abutting normal muscle. We conclude that MRI is capable of imaging acute histological changes. Appropriate development of a scale relating MR changes to acute and long-term histologic changes will allow us to optimize 3 D control and monitoring of ILT.     

Reactive carpal synovitis: initial experience with MR imaging

PURPOSE: To retrospectively evaluate the accuracy of various magnetic resonance (MR) imaging findings in the diagnosis of reactive carpal synovitis. MATERIALS AND METHODS: Institutional review board approval was obtained, and the need for informed consent was waived. This study was compliant with the Health Insurance Portability and Accountability Act. Thirty-five consecutive patients (19 male and 16 female patients; age range, 13-57 years) who underwent arthroscopy and MR imaging within 4 weeks of surgery were evaluated by two reviewers for the following potential findings of synovitis: (a) distention of the pisotriquetral recess by fluid, (b) distention of the radial and/or prestyloid recess, (c) synovial enhancement (in patients who received contrast material), (d) amount of dorsal capsule distention, and (e) the location of bone marrow edema, if any. The chi2 and paired t tests were used to assess these findings in patients with and patients without arthroscopically proved synovitis. The sensitivity, specificity, positive and negative predictive values, and accuracy of these findings in the detection of synovitis were calculated. RESULTS: Fluid in the pisotriquetral recess was seen in nine of the 14 patients with synovitis and five of the 21 patients without synovitis (P = .018). Distention of the radial and/or prestyloid recess was observed in six of the 14 patients with synovitis and two of the 21 patients without synovitis (P = .027). Among the 24 patients who received contrast material, synovial enhancement was seen in seven of eight patients with synovitis and three of 16 patients without synovitis (P = .002). The dorsal capsule measured 1-7 mm (mean, 3.07 mm) in the 14 patients with synovitis and 2-7 mm (mean, 3.76 mm) in the 21 patients without synovitis (P = .193). Although bone marrow edema was seen globally in similar frequencies (nine of 14 patients with synovitis, nine of 21 patients without synovitis), pisotriquetral bone marrow edema was seen only in patients with synovitis (two of nine patients). CONCLUSION: Fluid in the pisotriquetral recess, enhancing synovium, and, less commonly, pisotriquetral bone marrow edema are MR imaging findings that may help in the diagnosis of reactive carpal synovitis.