Acquisition Single-shot Turbo Spin-echo Research Articles

A Systematic Review of Diffusion-Weighted Magnetic Resonance Imaging in the Assessment of Postoperative Cholesteatoma

A systematic review to determine whether the diffusion-weighted (DW) magnetic resonance imaging scan can reliably detect residual or recurrent cholesteatoma after mastoid surgery. A systematic review. Databases including EMBASE, MEDLINE, CINAHL, Web of Science, and Cochrane Review were searched for studies published without language restriction from the start of the databases. Additional studies were identified from cited references. Initial search identified 402 publications, of which 16 studies met the inclusion criteria for the systematic review. The DW imaging (DWI) scan was used to detect residual or recurrent cholesteatoma and subsequent second-look surgery was performed to correlate the findings. Studies were assessed for their selection of patients for radiologic investigations, imaging parameters, and subsequent surgery. Outcome measures included sensitivity, specificity, positive and negative predictive values of the DWI, and the incidence and size of residual or recurrent cholesteatoma. Two different modalities of DWI sequences have been described. Eight studies with 225 patients analyzed echo-planar imaging (EPI) and 8 studies with 207 patients described the "non-EPI" scanning techniques. Non-EPI parameters are more reliable in identifying residual or recurrent cholesteatoma with sensitivity, specificity, and positive and negative predictive values of 91%, 96%, 97%, and 85%, respectively. The available evidence suggests that non-EPI such as half-Fourier acquisition single-shot turbo spin echo sequences are more reliable in identifying residual or recurrent cholesteatoma. This is a promising radiologic investigation; however, we think further studies are required with more patients and long-term results to establish its place as an alternative to a second-stage surgery after canal wall up surgery.

MR sialography of iatrogenic sialocele: comparison with conventional sialography

The objective of this study was to compare the conventional sialography with MR sialography in a series of patients with iatrogenic sialocele (sialocyst). 50 salivary glands in 39 patients with suspected inflammatory disease of the salivary gland underwent conventional sialography and MR sialography. Out of these 39 patients, 6 patients (age range: 16-35 years; 4 males and 2 females; mean age: 23.8 years) had sialoceles and formed our study group. MR sialography findings were compared with conventional sialography findings regarding demonstration of ductal anatomy, the cyst and its communication with the ductal system. MR sialography demonstrated the site of communication of the sialocyst with the ductal system in all six patients. MR provided additional information over conventional sialography in five cases. In four cases, the ductal system proximal to the cyst was not opacified on digital sialography but was well visualized in all cases by MR sialography. Constructive interference in steady-state (CISS) sequence demonstrated the intraglandular ducts and communication of cysts with ducts better than half-fourier acquisition single-shot turbo-spin echo (HASTE) images. Our preliminary results suggest that MR sialography is a robust, non-invasive method for demonstrating the ductal system up to second-order branches, the site of ductal injury and the focal cystic lesion. MR provided at least the same information as conventional sialography in the evaluation of site of communication but provided additional information about the sialocyst and upstream ductal system in five cases. Being a non-invasive modality, we recommend MR sialography as the investigation of choice in the evaluation of an iatrogenic sialocyst.

HASTE diffusion-weighted mri: reliability for detection of cholesteatoma

To assess the detection efficiency of Half-Fourier acquisition single-shot turbo spin-echo (HASTE) diffusion-weighted magnetic resonance imaging (MRI) for cholesteatoma. A total of 21 patients with suspected primary (n=16) or recurrent cholesteatoma (n=5) underwent MRI in a 1.5 Tesla scanner using an adapted protocol for cholesteatoma detection that included a coronal HASTE diffusion-weighted MRI sequence. The cholesteatoma diagnosis was based on evidence of a hyperintense lesion at b-1000 on diffusion-weighted images. The imaging findings were correlated with findings from surgery or clinical evaluations in all patients. HASTE diffusion-weighted MRI successfully detected 11 primary and 5 recurrent lesions out of 17 cholesteatomas (sensitivity, 94.1%). One primary cholesteatoma with a diameter of 4-5 mm was missed. MRI of patients without cholesteatoma were correctly interpreted as negative for cholesteatoma (specificity, 100%). The positive and negative predictive values for the HASTE diffusion-weighted MRI in detecting cholesteatoma were 100% and 80%, respectively. HASTE diffusion-weighted MRI offers great promise for cholesteatoma screening. The addition of this sequence to the posterior fossa MRI protocol may preclude unnecessary cholesteatoma surgery.

HASTE MRI in the assessment of children with hydrocephalus

Background Recent reports and our clinical experience have shown the usefulness of rapid-acquisition MRI in evaluating children with hydrocephalus. An axial HASTE (i.e. Half-Fourier Acquisition Single-shot Turbo Spin Echo Magnetic Resonance Imaging) MRI study acquires clinically useful images in seconds without exposing children to the risks of ionizing radiation or sedation. The current report reviews the Seattle Children’s Hospital experience with rapid acquisition MRI in shunted children with attention to ventricular size, overall image quality, motion artifact, and catheter visualization. Materials and methods All HASTE MRIs obtained at Seattle Children’s Hospital over two-years were reviewed by two evaluators on scales of overall image quality, catheter visualization, motion artifact, and ventricular size. Relationships among these factors were sought. Results Overall image quality was rated very good or excellent in 94% of the studies reviewed, while only one study was graded as poor. Significant motion artifact was noted in 7% while 77% had little or no motion artifact. Catheter visualization was rated as good or excellent in 57% of studies reviewed, poor in 36%, and misleading in 7%. Small ventricular size showed a significant correlation with poor catheter visualization (Pearson correlation coefficient = .575; p<.00001). Ventricular enlargement concerning for shunt malfunction on HASTE imaging correlated with operative findings of shunt malfunction in 100% of cases taken to the OR based on HASTE imaging. Conclusions Our study adds further support to the emerging evidence that HASTE MRI is an adequate substitute for CT scanning allowing for reduced utilization of CT imaging and resultant exposure to ionizing radiation. Visualization of catheter position remains suboptimal with HASTE MRI, particularly when ventricles are small; however, shunt malfunction can be adequately determined based on ventricular size alone in the majority of cases.

Examining the Relationship between the Lung-to-Head Ratio Measured on Ultrasound and Lung Volumetry by Magnetic Resonance in Fetuses with Isolated Congenital Diaphragmatic Hernia

Purpose: In fetuses with isolated congenital diaphragmatic hernia (CDH), lung development can be measured by the lung-to-head ratio (LHR) using ultrasound as well as by lung volumetry determined by fetal magnetic resonance imaging (MRI). We aimed to investigate their relationship as well as to analyze the factors that may have an impact on it. Material and Methods: In 153 consecutive fetuses with isolated CDH, both the LHR and total fetal lung volume (TFLV) were measured. The observed LHR was calculated by dividing the lung area by the head circumference. On MRI, planimetric measurements of ipsilateral, contralateral and TFLV were performed on T₂-HASTE (half-Fourier acquisition single-shot turbo spin echo) sequences in transverse as well as coronal or sagittal planes. All values were expressed as a ratio of what was observed over what is expected in a gestational age-matched normal fetus. Secondary analyses were performed for right- versus left-sided hernia and for measurements made prior to 25 weeks’ gestation. A multivariate linear regression approach was used to determine the influence of the independent variables such as observed/expected (O/E) LHR, gestational age, liver position and CDH side on the dependent variables O/E TFLV and O/E contralateral FLV, and to determine the optimal formulas for calculation of the O/E TFLV as well as contralateral FLV. Results: In total, 200 pairs of measurements were obtained between 20 and 37 weeks’ gestation (median 26+6). There was a significant association between the O/E contralateral FLV and O/E LHR (R² = 0.44; p < 0.001) as well as between the O/E TFLV and the O/E LHR (R² = 0.37; p < 0.001). After adding the independent variables that were first shown to be significant on univariate analysis, the multiple regression analysis demonstrated that gestational age (p = 0.017) and side of the defect (p < 0.001) were predictive of O/E LHR (p < 0.001) and strongly improved the estimation of O/E TFLV (R² = 0.43 instead of 0.37 when using O/E LHR only). In terms of estimating O/E contralateral FLV, only the O/E LHR was a significant (p < 0.001) independent predictor (R² = 0.44). These correlations also applied when considering only left-sided CDH cases. For measurements done prior to the third trimester, the O/E LHR (p = 0.034), gestational age (p = 0.035) as well as liver herniation (p = 0.029) were significantly correlated to the O/E TFLV (R² = 0.33). In terms of predicting the O/E contralateral FLV (R² = 0.25), only O/E LHR (p = 0.008) and gestational age (p = 0.037) were useful predictors. Conclusion: Measurement of the O/E LHR on ultrasound allows a good estimation of the O/E contralateral FLV as well as TFLV as measured by MRI. Whereas the additional parameters such as gestational age, liver position and side of the defect did not improve the estimation of the contralateral FLV, they did so for estimating the TFLV.

Magnetic resonance imaging of intramuscular metastases

The aim of the present study was to analyse magnetic resonance findings of intramuscular metastases (IM) in a relatively large series. From January 2000 to January 2010, 28 patients (207 metastases) were retrospectively identified in the radiological database of the Martin-Luther-University. Several different scanning protocols were used depending on the localisation of IM. In 12 patients diffusion-weighted (DW) images were obtained with a multi-shot SE-EPI sequence. Apparent diffusion coefficient (ADC) maps were also calculated. Furthermore, fusion images were manually generated between the DW and half-Fourier acquisition single-shot turbo spin echo (HASTE) images. On T2-weighted images,97% of the recognised IM were hyperintense in comparison to unaffected musculature, and 3% were mixed iso- to hyperintense. On T1-weighted images most IM (91%) were homogeneously isointense in comparison to muscle tissue, whereas 4% were hypointense, and 5% lightly hyperintense. ADC maps were calculated for 91 metastases ranging from 0.99 to 4.00mm(2)s(-1) (mean value 1.99 ± 0.66). ADC values of low (<1.5) signal intensity (SI) were identified in 26%, moderate SI (from 1.5 to 3.0) in 68%, and high SI (>3.0) in 6%. Of the IM that were investigated with contrast medium, 88.5% showed marked enhancement. It was homogeneous in 88% and heterogenous in 6%. Rim enhancement with central low attenuation was seen in 6%. There was no difference in enhancement characteristics with respect to ADC values or fusion patterns. Peritumoral enhancement was identified in 2.4%. Magnetic resonance features of muscle metastases are relatively typical and consist of round or oval intramuscular masses with well-defined margins, marked enhancement, low or moderate ADC values, and moderate to high signal intensity on fusion images.

Feasibility of 3-T MRI for the evaluation of Crohn disease in children

Crohn disease (CD) is a chronic inflammatory bowel disease that can affect any part of the gastrointestinal tract from the oral cavity to the anal canal. It occurs in all ages and is a significant cause for morbidity in children. Interest in MRI evaluation of CD has increased because of the concern regarding cumulative radiation dose from contrast fluoroscopic studies and CT. Several reports have demonstrated MRI to be a useful technique for CD. Most of these studies were performed at 1.5-T field strength. Imaging at a higher field strength, with a greater signal-to-noise ratio, has the potential of reducing scan times and increasing the resolution. However, there is a concurrent increase in artefacts, and these can be pronounced with abdominal imaging at 3 T. To determine the feasibility of 3-T MRI for CD in children and to assess the value of different sequences and the effect of artefacts that could potentially limit the role of bowel MR imaging at higher field strengths. A retrospective study of 46 children with biopsy-proven CD (ages 8-19 years, 53% boys) was performed. Sixty-eight consecutive MRI studies were performed on a 3-T scanner between 2005 and 2007; 42 of the abdomen (62%) and 26 of the pelvis/perineum (38%). Sorbitol was administered for the abdominal studies; orally for 36/42 (86%) studies and via a naso-jejunal (NJ) tube for 6/42 (14%) studies. For the abdomen, T2-W half-fourier acquisition single-shot turbo spin-echo (T2-W HASTE), true steady-state free precession (true FISP), pre-contrast and contrast-enhanced (CE) T1-volume interpolated gradient-echo (T1-W VIBE) and CE T1-W fast low-angle shot (T1-W FLASH) sequences were performed. For the perianal and pelvic assessment, fat-saturated T2-W turbo spin-echo (TSE), pre-contrast and CE T1-W FLASH or VIBE sequences were performed. The sequences were scored for diagnostic quality by two paediatric radiologists for visualisation of the bowel wall, whether normal or pathological and the visualization of extra intestinal manifestations. The effects of distension, susceptibility artefact and motion were assessed. Six (14%) abdominal MRI studies were normal. Thirty-six (86%) were abnormal with good correlation with endoscopic findings. The pelvic and perianal MRI studies were all abnormal (26/26, 100%) with good correlation with proctoscopy and examination under anaesthesia. All the sequences had high average scores (greater than or close to 3), except true FISP with a score of 2.4. The score was greatest in those who had NJ administration of sorbitol; however, satisfactory distension was also possible with oral administration of contrast. True FISP was the sequence most affected by a combination of suboptimal distension and artefact from colonic contents. With adequate distension, true FISP image quality improved remarkably. The overall score of this sequence was satisfactory in the absence of susceptibility and movement artefact. With appropriate attention to technique, with optimal distension and control of movement, high-quality, 3-T assessment of the abdomen, pelvis and perineum is possible. All sequences used at 1.5 T can be used at 3 T, however true FISP was the most prone to artefact.

MRI and MR sialography of juvenile recurrent parotitis

Juvenile recurrent parotitis (JRP) is the second most common inflammatory salivary gland disease of childhood, after mumps. Diagnosis of JRP is usually based on clinical history of recurrent unilateral or bilateral parotid swelling and demonstration of sialectasis. Conventional sialography, digital sialography, US, MRI and sialoendoscopy have been used as investigative tools for the diagnosis of JRP. MR sialography is increasingly recognized as a useful supplement to sialography in salivary duct disorders. To describe the MRI and MR sialographic findings in children with JRP. MR Sialography was performed using T2-weighted three-dimensional constructive interference in steady-state (CISS) and half fourier acquisition single-shot turbo spin-echo (HASTE) sequences in 62 children with inflammatory salivary gland disease. Out of these 62 children, 6 had JRP. Axial T1- and T2-W images were also performed. The main parotid duct was normal in all six children with JRP. High signal intensity focal lesions suggestive of sialectasis were seen involving both parotid glands in all six children. CISS sequence demonstrated the intraglandular ducts and sialectasis better than HASTE images. MRI and MR sialography can non-invasively delineate the parenchymal and ductal system abnormalities of the parotid glands in children with JRP. Although MR and MR sialography cannot substitute US, they can accurately depict findings such as sialectasis and signal intensity changes in the parotid gland depending upon the phase of the disease (acute vs. chronic inflammation). The radiologist should be familiar with MR findings of JRP.

Fetal cleft lip with and without cleft palate: Comparison between MR imaging and US for prenatal diagnosis

Objective To describe the magnetic resonance (MR) imaging findings of fetal CL/CP and evaluate its diagnostic value. Methods and materials Twelve fetuses with CL/CP diagnosed by transabdominal US underwent MR imaging within 2 days of US. Half-Fourier acquisition single-shot turbo spin echo (HASTE) sequence on T2-weighted images was performed on sagittal, coronal, and axial planes anatomic to the fetuses during maternal breath holding. US and MR imaging findings were compared with final diagnoses obtained from post-natal physical examination or fetal autopsy. Results Final diagnoses confirmed incomplete midline cleft lip ( n = 1), unilateral cleft lip and palate ( n = 7), bilateral cleft lip and palate ( n = 1), midline cleft lip and palate ( n = 3). US and MR imaging diagnosed all 12 fetuses with cleft lip and the laterality. 5 (45.5%) of 11 cleft palates were identified with US, 2 of 7 fetuses with unilateral cleft palate, 2 of 3 fetuses with midline cleft palate, and one fetus with bilateral cleft palate. On MR imaging, 10 (91%) of 11 cleft palates were correctly detected. One fetus with unilateral cleft palate was not detected. No false-positives occurred. Conclusion MR imaging is valuable for diagnosis of fetal CL/CP. It can demonstrate additional findings and provide more information compared with US.

Magnetic resonance sialography using CISS and HASTE sequences in inflammatory salivary gland diseases: Comparison with digital sialography

Inflammatory conditions are the most common pathology affecting the salivary glands. Magnetic resonance (MR) sialography has emerged as an alternative to conventional sialography for evaluation of inflammatory salivary gland diseases. To prospectively evaluate the role and diagnostic accuracy of MR sialography in the diagnosis of inflammatory salivary gland disease. Thirty-seven glands in 28 patients (19 males and nine females; mean age 31 years, range 3-65 years) presenting with inflammatory salivary gland disorders underwent MR sialography. Conventional sialography was used as the gold standard and was performed in 26 patients (34 glands). Thus, comparative evaluation was done in 26 patients (34 glands). Axial T1-weighted (T1W) and fat-suppressed T2W sequences, a constructive interference in steady state (CISS) sequence in the axial plane with maximum intensity projection (MIP)/multiplanar reformation (MPR) done in the axial and sagittal oblique planes, and a half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence in the sagittal oblique direction were performed. Main salivary gland duct was visualized in 32 glands (94.1%) with MR sialography, and in all 34 (100%) glands with conventional sialography. Calculus and strictures were well demonstrated by MR sialography. MR sialography was superior for demonstration of the ductal system proximal to calculus/strictures. Sensitivity and specificity for diagnosis of specific pathology were 87% and 100% with CISS sequence and 90% and 75% with HASTE sequence, respectively. On using a combination of CISS and HASTE sequences, the sensitivity, specificity, and positive and negative predictive values in the diagnosis of specific pathology were 93%, 100%, 100%, and 64%, respectively. MR sialography using CISS and HASTE sequences is a promising technique and has the potential to replace conventional sialography in patients with inflammatory salivary gland disorders.

Usefulness of Postcontrast T2-Weighted Images in Shortening the Total Scan Time of a Gadoxectic Acid Enhanced MRI of the Liver: a Comparison between Precontrast and Postcontrast T2-Weighted Images

Purpose: We evaluated the effects of gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) on the overall image quality and lesion contrast of T2-weighted images (T2WI). Materials and Methods: We reviewed T2WI before and after Gd-EOB-DTPA enhancement in 50 patients with 41 focal liver lesions. Pre- and post-contrast T2WI were analyzed qualitatively and quantitatively. For the qualitative analysis, two abdominal radiologists, blinded to other findings in the study, retrospectively scored the image quality, lesion conspicuity, and artifacts. The quantitative analysis involved the measurement of the liver signal-to-noise ratio (SNR) and the lesion-to-liver contrast-to-noise ratio (CNR). Results: Image quality and lesion conspicuity were not significantly different among the respiratory-triggered T2-weighted turbo spin-echo sequence (T2TSE), Half-fourier acquisition single-shot turbo spin-echo (HASTE) sequence, and breath-hold T2-weighted gradient recalled-echo (GRE) sequences. However, there was a trend toward improved lesion conspicuity in post-contrast T2TSE. The quantitative analysis indicated that the SNR for post-contrast images was significantly higher than for pre-contrast images on T2TSE (p=0.04). No significant differences were seen in the CNR of focal lesions, but there was a trend towards an increase in the CNR for postcontrast T2WI of hepatocellular carcinoma. Conclusion: Compared to pre-contrast T2WI, post-contrast T2WI showed no handicap in the overall image quality and lesion contrast. Therefore, to shorten the total scan time during Gd-EOB-DTPA enhanced MRI, pre-contrast T2WI can be replaced by post-contrast T2WI.

BOLD fMRI using a modified HASTE sequence

For more than a decade, turbo spin echo (TSE) pulse sequences have been suggested as an alternative to echo planar imaging (EPI) sequences for fMRI studies. Recent development in parallel imaging has renewed the interest in developing more robust TSE sequences for fMRI. In this study, a modified half Fourier acquisition single-shot TSE (mHASTE) sequence has been developed with a three-fold GRAPPA to improve temporal resolution as well as a preparation time to enhance BOLD sensitivity. Using a classical flashing checkerboard block design, the BOLD signal characteristics of this novel method have been systematically analyzed as a function of several sequence parameters and compared to those of gradient-echo and spin-echo EPI sequences. Experimental studies on visual cortex of five volunteers have provided evidence suggesting that mHASTE can be more sensitive to extra-vascular BOLD effects around microvascular networks, which leads to more accurate function localization. The studies also show that the activation cluster size in mHASTE increases with the refocusing RF flip angle and TE while decreasing with the echo number (ncenter) used to sample the k-space center. Compared to spin-echo EPI, mHASTE incurs an ∼50% reduction in activation cluster size and an ∼20% decrease in BOLD contrast. However a higher signal-to-noise ratio and a spatially more uniform temporal stability have been observed in mHASTE as compared to the EPI sequences when the scan times are held constant. With further refinement and optimization, mHASTE can become a viable alternative for fMRI in situations where the conventional EPI sequences are limited or prohibitive.

Time-efficient fast spin echo imaging at 4.7 T with low refocusing angles

An implementation of fast spin echo at 4.7 T designed for versatile and time-efficient T(2)-weighted imaging of the human brain is presented. Reduced refocusing angles (alpha < 180 degrees) were employed to overcome specific absorption rate (SAR) constraints and their effects on image quality assessed. Image intensity and tissue contrast variations from heterogeneous RF transmit fields and incidental magnetization transfer effects were investigated at reduced refocusing angles. We found that intraslice signal variations are minimized with refocusing angles near 180 degrees, but apparent gray/white matter contrast is independent of refocusing angle. Incidental magnetization transfer effects from multislice acquisitions were shown to attenuate white matter intensity by 25% and gray matter intensity by 15% at 180 degrees; less than 5% attenuation was seen in all tissues at flip angles below 60 degrees. We present multislice images acquired without excess delay time for SAR mitigation using a variety of protocols. Subsecond half Fourier acquisition single-shot turbo spin echo (HASTE) images were obtained with a novel variable refocusing angle echo train (20 degrees < alpha < 58 degrees) and high-resolution scans with a voxel volume of 0.18 mm(3) were acquired in 6.5 min with refocusing angles of 100 degrees.

MR imaging of aortic coarctation

Aortic coarctation accounts for 5%-10% of all congenital heart diseases and represents 7% of critically ill infants with heart disease. Magnetic resonance (MR) imaging allows the study of this disease with several advantages in comparison with conventional angiography, transesophageal echocardiography, and computed tomography. The MR protocol applied at our institution for both diagnosis and follow-up after surgical or endovascular treatment consists of four steps: morphologic study, cine MR study, flow analysis, and MR angiography (MRA). The first three sequences are acquired during breath-hold and with electrocardiographic gating. Anatomy is well depicted with dark-blood half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences. Cine true-fast imaging with steady-state precession (true-FISP) sequences show not only morphologic features but also blood-flow changes inside the aorta. Gradient-echo sequences for phase-velocity mapping allow flow analysis. Application of Bernoulli's equation--here briefly presented and discussed--allows for calculation of the pressure gradient caused by the coarctation. MRA, acquired with a breath-hold three-dimensional T1-weighted gradient-echo sequence and intravenous administration of paramagnetic contrast material, allows for optimal depiction of the aortic lumen, with a panoramic view of the whole aorta, its main branches and possible collateral circulation.

Role of diffusion weighted magnetic resonance imaging (DW MRI) in classification of liver hydatid cysts and differentiation of simple cysts and abscesses from hydatid cysts

The purpose of this study is to identify the role of diffusion-weighted magnetic resonance imaging (DW-MRI) in the classification of liver hydatid cysts (HCs) and their differentiation from simple cysts and liver abscesses. Twenty-two patients that were sent to our department with preliminary diagnoses of HCs or abscess were included in the study. Thirty lesions were evaluated. MRI included T1-weighted fast gradient echo, T2-weighted half-Fourier acquisition single-shot turbo spin echo, and DW single-shot echo planar pulse sequencing (b, 0, 50, and 1000 s/mm²). The apparent diffusion coefficient (ADC) values (mm²/s) of the HCs, abscesses, and simple cysts were calculated. No statistically significant difference was found between the ADC values of type 1 and 3 (P > 0.05) HCs and of simple cysts and type 1 HCs (P > 0.05). The ADC values of abscesses were significantly lower than those of type 1 and type 3 HCs, and simple cysts. No statistically significant difference was found between the ADC values of abscesses and type 4 HCs (P > 0.05). Type 4 lesions exhibited significantly lower ADC values in comparison to type 1 and 3 HCs. DW-MRI helps differentiate type 4 lesions from other cysts and can distinguish abscesses from hydatid cysts other than type 4 as well as from simple cysts. Type 1 HCs cannot be differentiated from simple cysts using ADC values alone, and type 4 lesions are indistinguishable from abscesses.

Differentiation of hepatic tumors by use of image contrast with T2-weighted MRI

Differentiation of hepatic tumors is often evaluated in terms of qualitative diagnostic performance. The signal intensity patterns of hepatic masses are known to differ on certain T2-weighted imaging sequences. In this study, we investigated the quantitative analysis of hepatic masses by using an index called the "T2-shine ratio." Fast-spin-echo (FSE), half-Fourier acquisition single-shot turbo spin echo (HASTE), and true-FISP sequences obtained with quick-imaging techniques during a single breath-hold were examined in 74 patients. T2-shine ratios were calculated by use of the signals of regions of interest (ROIs) placed on a tumor and peripheral tissue: the T2-shine ratio is defined as (tumor signal-liver signal)/liver signal. The rate of change in the T2-shine ratio was compared among three sequences of FSE, HASTE, and true-FISP. The T2-shine ratio of FSE deducted from HASTE was significantly higher for hepatic cysts than for other masses. The T2-shine ratio of HASTE deducted from True-FISP was less than zero for hemangioma. For the value that deducted the T2-shine ratio of HASTE from the T2-shine ratio of true-FISP, hemangiomas had a significantly lower value than did cysts and metastases (P < 0.05), but there was no significant difference from hepatocellular carcinomas (HCCs). Although liver cysts, cavernous hemangiomas, and other lesions could be differentiated, it was virtually impossible to distinguish HCCs from metastatic tumors. In conclusion, the quantitative analysis of hepatic tumors was able to differentiate among these lesions by use of the T2-shine ratio.

Application of magnetic resonance imaging to measure fasting and postprandial volumes in humans

Our aims were to measure the gastric volume response in excess of ingested meal volume (i.e. gastric accommodation), contribution of swallowed air to this excess, day-to-day variability of gastric volumes measured by MRI and their relationship to volumes measured by single-photon-emission computed tomography (SPECT). In 20 healthy volunteers, fasting and postprandial gastric volumes were measured after technetium(99m)-pertechnetate labeling of the gastric mucosa by SPECT and separately by MRI, using 3D gradient echo and 2D half-Fourier acquisition single-shot turbo spin echo (HASTE) sequences. Ten of these subjects had a second MRI exam to assess intra-individual variation. Thereafter, another 10 subjects had two MRI studies during which they ingested the nutrient in 30 or 150 mL aliquots. During MRI, the postprandial gastric volume change exceeded the ingested meal volume by 106 +/- 12 mL (Mean +/- SEM). The HASTE and gradient echo sequences distinguished air from fluid under fasting and postprandial conditions respectively. This postprandial excess mainly comprised air (61 +/- 5 mL), which was not significantly different when ingested as 30 or 150 mL aliquots. Fasting and postprandial gastric volumes measured by MRI were generally reproducible within subjects. During SPECT, postprandial volumes increased by 158 +/- 18 mL; gastric volumes measured by SPECT were higher than MRI. MRI measures gastric volumes with acceptable performance characteristics; the postprandial excess primarily consists of air, which is not affected by the mode of ingestion. Gastric volumes are technique specific and differ between MRI and SPECT.

Multimodality imaging of a right saphenous vein graft pseudoaneurysm

A 74-year-old man with a history that was significant for two-vessel coronary artery bypass grafting (CABG) surgery, underwent magnetic resonance cholangiopancreatography for evaluation of chronic pancreatitis. A complex cystic mass, measuring 2 cm × 2 cm was incidentally observed anterior to the right atrium on the axial T2-weighted magnetic resonance cholangiopancreatography half-Fourier acquisition single-shot turbo spin-echo (HASTE) image (Figure 1A). A subsequent transthoracic echocardiography confirmed the cystic mass, extrinsic to the right atrium, with no intracardiac communication following administration of agitated saline contrast (Figure 1B). Multidetector computed tomography identified a pseudoaneurysm of the right saphenous vein graft from previous CABG (Figure 1C). A three-dimensional, volume-rendered multidetector computed tomography image of the graft arising from the aorta and the pseudoaneurysm is shown in Figure 1D. Cardiac catheterization confirmed the presence of a discrete inlet communication into the saphenous vein graft pseudoaneurysm (Figure 1E). The patient underwent successful occlusion of the ostium of the pseudoaneurysm by a covered stent graft (JOSTENT [Abbott Laboratories, USA] 4.00 mm × 8 mm) and disappearance of the jet of contrast (Figure 1F). Figure 1) A A complex cystic mass (arrow) measuring 3 cm × 3 cm × 4 cm was incidentally observed anterior to the right atrium on the axial T2-weighted magnetic resonance cholangiopancreatography half-Fourier acquisition single-shot turbo spin-echo ... Saphenous vein graft pseudoaneurysms are a rare complication following CABG and warrant prompt recognition due to potential fatal complications (1). They are often asymptomatic, discovered as an incidental paracardiac or mediastinal mass using complementary cardiac imaging including echocardiography, computed tomography and cardiac magnetic resonance imaging (2). Although surgery has traditionally been the treatment of choice (3), percutaneous techniques such as coiled embolization or self-expanding stents are emerging alternative options (4).

Fetal MRI of the central nervous system: clinical relevance

Specific conditions of the mother sometimes reduce the quality of ultrasound. In these cases, fetal magnetic resonance imaging (MRI) can be performed after gestational week (GW) 18. Interpretation of subtle disorders or malformations becomes safe not before GW 23. Clinical development of children with central nervous system (CNS) disorders is not predictable with imaging alone. Statistical evidence and personal experience of the medical team are essential in counseling, but optimized imaging is helpful in being more precise. The value of fetal MRI (fMRI) is evaluated. Twenty-five pregnant women (30.5 +/- 4.5 years) were investigated by additional fMRI. Breath-hold technique with T2 half-Fourier acquisition single-shot turbo spin-echo and T1 FLASH-2D images in three dimensions with field of view of 350 x 400 mm. All cases have been correlated with postnatal MRI, ultrasound, and clinical follow-up. In all fetuses, diagnostic MRI was performed 3-10 days after ultrasound between GW 22 and 34 (GW 26.1 +/- 3.6). Sedation was not necessary. In eight cases of suspicious ultrasound, fMRI confirmed ultrasound findings. In 13 cases, additional diagnoses or exclusions of suspected findings could be established. Complete revision of diagnosis was realized in four cases. Findings could be confirmed by postnatal MRI in 11 patients. The clinical course was not predictable in cases with ambivalent prognosis. Prenatal diagnosis of CNS pathologies should result in parental counseling. Sufficient diagnostic information, statistical data, and experience of the involved professionals are essential. These results show that in detecting congenital CNS abnormalities fMRI is superior to ultrasound and should be considered in difficult cases.

Measurement of T1, T2, and magnetization transfer properties during embryonic development at 7 Tesla using the chicken model

To evaluate whether techniques of high field magnetic resonance imaging may be used to characterize embryonic tissue during proliferation and differentiation. Thirteen chicken embryos with incubation times between 5 days and 16 days have been measured in a small animal magnetic resonance imager (ClinScan, Bruker) at 7 Tesla using the built-in resonator. T1, T2-, and magnetization transfer imaging was performed using fast spin-echo with inversion recovery, half acquisition single shot turbo spin-echo, and spoiled gradient-echo sequences with and without off-resonance pulse, respectively. T1, T2, and magnetization transfer ratio (MTR) maps were calculated on a pixel-by-pixel basis. T1-, T2-, and MTR maps showed good image quality allowing for delineation of embryonic organs. During embryonic development, a decrease of T1 and T2 relaxation times was found, whereas, embryonic tissue typically showed an increase of magnetization transfer, for example, liver properties at day 5: T1 = 2431 +/- 163 ms, T2 = 122 +/- 12 ms, MTR = 9.2 +/- 4.2%; liver properties at day 16: T1 = 1763 +/- 89 ms, T2 = 71 +/- 4 ms, MTR = 16.9 +/- 2.2%. Embryonic tissues show changing relaxation and magnetization transfer properties during development, therefore, high field MRI seems suitable for characterization of tissue replacement derived from embryonic stem cells.