Advanced Methods in Dynamic Contrast Enhanced Arterial Phase Imaging of the Liver

Dynamic contrast enhanced (DCE) magnetic resonance (MR) imaging plays an important role in non-invasive detection and characterization of primary and metastatic lesions in the liver. Recently, efforts have been made to improve spatial and temporal resolution of DCE liver MRI for arterial phase imaging. Review of recent publications related to arterial phase imaging of the liver indicates that there exist primarily two approaches: breath-hold and free-breathing. For breath-hold imaging, acquiring multiple arterial phase images in a breath-hold is the preferred approach over conventional single-phase imaging. For free-breathing imaging, a combination of three-dimensional (3D) stack-of-stars golden-angle sampling and compressed sensing parallel imaging reconstruction is one of emerging techniques. Self-gating can be used to decrease respiratory motion artifact. This article introduces recent MRI technologies relevant to hepatic arterial phase imaging, including differential subsampling with Cartesian ordering (DISCO), golden-angle radial sparse parallel (GRASP), and X-D GRASP. This article also describes techniques related to dynamic 3D image reconstruction of the liver from golden-angle stack-of-stars data.

Value of in-flow inversion recovery sequence in diagnosis of Budd-Chiari syndrome / 实用放射学杂志

Objective To explore the feasibility of in-flow inversion recovery (IFIR)sequence of magnetic resonance imaging (MRI)at 1.5T in diagnosis of Budd-Chiari syndrome (BCS).Methods A total of 45 patients with Budd-Chiari syndrome diagnosed by surgery or interventional surgery in our institution were enrolled.The prerequisite of the study was that all medical imaging data including MRI and digital subtraction angiography (DSA)should be integrated.Then,the diagnostic accuracy rates between IFIR sequence and DSA were analyzed and compared.Results Of all 45 patients with BCS,40 (88.9%)were diagnosed accurately by IF-IR sequence,including typeⅠa in 10,typeⅠb in 14,typeⅡ in 10 and type Ⅲ in 6.Meanwhile,41 (91.1%)were diagnosed accu-rately by DSA,including typeⅠa in 8,typeⅠb in 14,typeⅡ in 13 and type Ⅲ in 6.No significant difference was showed in diag-nostic accuracy between two imaging methods (P >0.05).Spearman rank correlation analysis revealed that the diagnostic accuracy of IFIR sequence was highly consistent with that of DSA(r =0.853,P <0.001 ).However,there existed significant difference be-tween two methods in accurate diagnosis of typeⅠa and typeⅡ BCS (P <0.05).Conclusion MRI IFIR sequence at 1.5T is highly consistent with DSA in diagnosis and classification of BCS,which can be used as a reliable method of preoperative screening for BCS diagnosis.

Application of Two-dimensional 1H-31P Inverse NMR Pulse Sequence in Detection of Organophosphorus Chemical Warfare Agents and Related Compounds / 分析化学

Combined pulsed-field gradient, shaped pulses, and product operator calculations (algorithm), two-dimensional 1 H-31 P hetero-nuclear multiple quantum coherence ( HMQC) pulse sequence was established with the aid of C language. The result showed that coherent transfer path selection could be achieved by adjusting the ratio of two gradient strength ( g1 , g2 ) . The best ratio of g1 and g2 was -5:4 . The HMQC method based on the above sequence can be used for identifying the alkyl groups coupling with phosphorous nucleus. For the different alkyl groups, the sensitivity of this method decreased in the order methyl>isopropyl>ethyl>propyl. The limit of detection was about 10 mg/L. This method can be directly used for the screening and identification of phosphorus chemical warfare agents and related compounds.

The Development of RAGE Pulse Sequence with Clinical MRI Scanner / 中国医学物理学杂志

Objective:To implement rapid acquisition gradient echo(RAGE)pulse sequence in clinical MRI scaner.Methods:Pascal language is engaged to edit source code.Number of slice excited,order of phase encoded,phase recycle of RF pulse,NEX,on/off of the gradients,and so on are all controlled by sequence parameters.SI×N_(phase)×N_(slice) data of 32 bctys were allocated to restore the k space.Source code of sequence was compiled with executable file and is loaded to RINMR software.Image of human brain are acquired.The experiment has been conducted on 0.36T permanent MRI system.Resuits:In the case of 256×256 matrix acquisition,time of single slice is 4 seconds.The resolution and SNR of the image are all adquately satisfy the clinical application.

Relationship between contrast pulsed sequencing parameters and changes of placental vascular bed in different stage of pregnant rats / 中国医学影像技术

Objective To quantitatively measure the perfusion parameters of placenta in different stage of pregnant rats using contrast-enhanced ultrasonography (CEUS) with contrast pulsed sequencing (CPS), and to analyze the relationship between perfusion parameters and changes of placental vascular bed. Methods Sixty healthy pregnant rats in according to the requirements of the experiment was divided into three groups: 15 days, 17 days and 20 days of gestation with 20 animals in each group. One blous injection of SonoVue (Sonovue 1.0 ml/kg) via a tail vein was administered to each rat, and the time-intensity curves (TIC) of placenta and uterine muscle wall were drawn with ACQ using CPS technique with MI 0.20, and the perfusion parameters were calculated. Then 4 μm vertical placenta sections were cut and stained with hematoxylin and eosin. Surface area densities of placental maternal blood space was measured with image analysis software. Results The peak intensity (PI) of 17 days and 20 days was higher than that of 15 days pregnant rats (P＜0.05). There was no difference in PI between 17 days and 20 days (P＞0.05), and nor of arrivel time (AT) and time-to-peak (TTP) (P＞0.05) among the three groups. There was significant difference of surface area densities of placental maternal blood space among the three groups (P＜0.05). PI was positively correlated to the surface area densites of placenta (P＜0.05). Conclusion There is close relationship between peak intensity and area densities of placental maternal blood space. CPS technique can sensitivly detect changes of the placenta vascular bed in different stage of pregnant rats.

Design and optimization of pulse sequence for quantitative measurement of ?-aminobutyric acid concentration using MR spectroscopy / 国际生物医学工程杂志

Objective To design and optimize the MRS pulse sequence which used to measure gamma-aminobutyric acid(GABA) in vivo. Methods In-depth research for the MRS sequence was carried out and a theoretical analysis and simulation by software using product-operator algebra for the design and optimization of pulse sequence was discussed. Results Through the simulation of MRUI software, Cr signal at ?3.0 was seen to be suppressed and the weak GABA signal was displayed clearly. Conclusion The sequence was designed and optimized. Method to increase the efficiency and the stability of the measurement was studied. Our research gives theoretical preparation for the coming programming work.

Usefulness of Post-enhanced Delayed FLAIR Imaging for Making the Diagnosis of Leptomeningitis

PURPOSE: To evaluate the usefulness of post-enhanced delayed FLAIR (fluid-attenuated inversion-recovery) images in the diagnosis of leptomeningitis. MATERIALS AND METHODS: We obtained the pre- and post-enhanced FLAIR images of 7 rabbits every hour after infusing triple doses of contrast, and we measured the signal intensities of the CSF (cerebrospinal fluid) and the brain parenchyma. Five leptomeningitis patients and 5 volunteers were enrolled to obtain the pre-enhanced FLAIR images, the early post-enhanced FLAIR images and the delayed post-enhanced FLAIR images, with using a standard dose of contrast, and to measure the signal intensities of the CSF and brain parenchyma. The statistical significances were determined by a mixed procedure and the Wilcoxon rank-sum test (p<0.05). RESULTS: In the rabbits, the signal intensities of the CSF began to increase after an hour of contrast infusion, but those of the parenchyma did not increase. The time of maximum CSF enhancement was 2 hours after contrast infusion (p<0.001; standard estimate=750.43) and we obtained the post-enhanced delayed FLAIR images for clinical studies according to this result. The signal intensities of the CSF in the subarachnoid space were higher in the patient group compared with those of the normal control group on both the early post-enhanced FLAIR images and the delayed post-enhanced FLAIR images (p=0.0096) (p=0.0391). In the patient group, changes of signal intensities of the CSF in the subarachnoid space were more conspicuous on the delayed post-enhanced FLAIR images than on the early post-enhanced FLAIR images (p=0.0042). However, those of the parenchyma were not different in either group. CONCLUSION: The post-enhanced delayed FLAIR images obtained at 2 hours after contrast infusion are more useful for making the the diagnosis of leptomeningitis than are the post-enhanced early FLAIR images.

Histogram Analysis of Noise Performance on Fractional Anisotropy Brain MR Image with Different Diffusion Gradient Numbers

PURPOSE: We wished to analyze, qualitatively and quantitatively, the noise performance of fractional anisotropy brain images along with the different diffusion gradient numbers by using the histogram method. MATERIALS AND METHODS: Diffusion tensor images were acquired using a 3.0 T MR scanner from ten normal volunteers who had no neurological symptoms. The single-shot spin-echo EPI with a Stejskal-Tanner type diffusion gradient scheme was employed for the diffusion tensor measurement. With a b-valuee of 1000 s/mm2, the diffusion tensor images were obtained for 6, 11, 23, 35 and 47 diffusion gradient directions. FA images were generated for each DTI scheme. The histograms were then obtained at selected ROIs for the anatomical structures on the FA image. At the same ROI location, the mean FA value and the standard deviation of the mean FA value were calculated. RESULTS: The quality of the FA image was improved as the number of diffusion gradient directions increased by showing better contrast between the WM and GM. The histogram showed that the variance of FA values was reduced as the number of diffusion gradient directions increased. This histogram analysis was in good agreement with the result obtained using quantitative analysis. CONCLUSION: The image quality of the FA map was significantly improved as the number of diffusion gradient directions increased. The histogram analysis well demonstrated that the improvement in the FA images resulted from the reduction in the variance of the FA values included in the ROI.

MRI Study the Acute Disseminated Encephalomyelitis(ADE) Using FastFluid-attenuated Inversion Recovery Pulse Sequence / 实用放射学杂志

Objective To evaluate the clinical application of fast fluid-attenuated inversion recovery(FLAIR) pulse sequence in MRI study of ADE.Methods Thirty cases with ADE were studied with fast FLAIR sequence and T 2 weighted spinecho sequence.The results were compared in terms of image quality.Results We found the fast-FLAIR could suppress CSF signal effectively,and more lesions were displayed on FLAIR images than on turbo SE T 2-weighted images.The extent of the lesions and the contrast between lesions and normal brain tissue were demonstrated better with fast-FLAIR sequence.Conclusion The lesions in ADE are demonstrated on fast-FLAIR sequence better than on turbo SE T 2 weighted sequence and FAST-flair could be a complementing modality to display lesions in ADE.

The Evaluation of ROC Curve in Qualitative and Quantitative Analysis of Pancreatic Diseases on Fat Saturation FSPGR Sequence / 实用放射学杂志

Objective To evaluate the accuracy of fatsuppressed fast spoiled gradient echo(FSPGR) T_1WI in detection of pancreaticdisease using the receiver operating characteristic curve(ROC).Methods The pancreas were evaluated in 92 subject investigated(57normal and 35 with pancreatic disease) with fat saturation FSPGR T_1WI.The signal intensity(SI) ratio of pancreas relative to liver and spleen was quantitatively measured using regions of interest(ROIs),then qualitatively assessed by one independent observers.Results The mean values of pancreas-liver ratios and pancreas-spleen ratios between a normal and an abnormal pancreas were significantlydifferent.Thearea under ROC curve of the pancreas-liver SI ratio and the pancreas-spleen SI ratio was 0.92?0.03 and 0.91?0.04,respectively.There was no statistically significant difference between quantitative and qualitative analysis for the diagnosis of pancreatic disease when using liver as comparable standard.The sensitivity of qualitative pancreas in comparison with liver was 86.7%,while specificity was 91.2%.Conclusion When the SI ratio of pancreas-liver is used to distinguish normal from abnormal pancreas,qualitative analysis by observers is as accuracy as quantitative measurement.

2D-FIESTA Sequence of MRI in the Evaluation of the Biliary Tract for the Infants and Young Children / 实用放射学杂志

Objective To evaluate the diagnostic value of 2D-FIESTA sequence of MRI in the detection of the biliary tract lesions in infant and young children patients(less than 3 years).Methods 8 infant and young children patients were examined by MRI to evaluatetheir biliary tract.Images were obtained with a 1.5T whole body MRI system(GE Medical System,Milwakee,Wis,USA),using theCARDIAC coil.The patients were sedated by chloral hydrate orally or by pentobarbital sodium intravenously.No contrast agents wererequired.All of the axial,coronal and sagittal images were reviewed on an independent workstation and maximum intensity projection(MIP) and multiplanar reformations(MPR) techniques were applied.Results The 2D-FIESTA pulse sequence results in images in which the hepatic vascular structures and the biliary tract were highlighted.In this way,a clear visualization of the hepatic vessels and biliarytract could be obtained in all 8 cases.MRI could demonstrate the anatomy and pathology of post-transplantation changes in 3 patients,choledochal cysts in 2 patients,anomalous connection between the bile and pancreatic ducts in 1 patient.All the abnormalities were proved by operation.2 examinees were diagnosed normal by MRI and were confirmed by follow-up.Conclusion 2D-FIESTA is a fast sequence that allows the high quality images to be generated without breath-hold and without administration of contrast material.It has a potential wide application in the evaluation of biliary tract in the infant patients.

Assessment of Focal Liver Lesions with 4-Phase Dynamic FLASH MR Imaging: Usefulness of Early Image Acquisitionfor Characterization of Arterial Phase

PURPOSE: To document the usefulness of early image acquisition using the contrast-enhanced dynacic MR imagingfor characterization of various focal hepatic lesions during the arterial phase. MATERIALS AND METHODS:Seventy-nine patients with 145 focal liver lesions (71 hemangiomas, 59 hepatocellular carcinomas and 15metastases) underwent breathhold dynamic MR imaging using a fast low-angle shot sequence. After obtainingunenhanced T1-weighted images, four phase MR images were obtained 10, 35, 60 and 300 seconds after starting theinjection. Patterns of contrast enhancement were analyzed for each lesion, with an emphasis on first phase images. RESULTS: Forty-two of the 59 HCCs (71%) showed prominent contrast enhancement during the first phase. HCCssmaller than 2cm in diameter showed a more homogeneous enhancement pattern than those which measured 2cm ormore(24/25 vs 12/17;P<.05). Hemangiomas showed a globular enhancement pattern during the same phase in 51 of 71cases (72%), a finding which was more apparent in those whose diameter was 2cm or more(35/54 vs 16/17, p<.05).During the first phase of imaging, 12 of the 15 metastases showed peripheral enhancement of their thick rim. CONCLUSION: The use of early image acquisition on dynamic MR sequences is helpful in character-izing lesionsaccrding to their pattern of contrast enhancement.

Role of EPI in Diagnosing Cavernous Hemangioma & Small HCC: Comparision with Fast T2-Weighted MR Imaging

PURPOSE: To compare single-shot echo-planar MR imaging(EPI) with breath-hold fast T2-weighted imaging(HASTEor Turbo spin-echo T2WI) for evaluation of the role of EPI in distinguishing small hepatocellular carcinoma fromcavernous hemangioma. MATERIALS AND METHODS: We retrospectively evaluated MR images of 35 patients (21 cases ofsmall HCC and 14 cases of cavernous hemangioma). EPI and breath-hold fast T2WI images were obtained and comparedon the basis of lesion detection sensitivity, lesion-to-liver signal intensity ratio(SIR), contrast ratio(CT), andlesion-to-liver contrast to noise ratio(CNR). RESULTS: For the detection of small HCC, the sensitivity of EPI andbreath-hold fast T2WI were equal in 14 of 21 cases(71.4%). The detection sensitivity of cavernous hemangioma withEPI and breath-hold fast T2WI was 100%(14/14). Mean SIR on breath-hold fast T2WI was 2.02+/-0.45 for small HCC and3.65+/-0.97 for cavernous hemangioma; on EPI, the corresponding figures wer 2.91+/-0.57 and 6.98+/-1.37. Mean CR onbreath-hold fast T2WI was 1.16+/-0.58 for small HCC and 2.65+/-0.57 for cavernous hemangioma; On EPI, the figuresobtained were 2.27+/-0.52 and 6.26+/-2.19, respectively. Mean CNR on breath-hold fast T2WI was 14.24+/- 4.098 forsmall HCC and 50.28+/-10.96 for cavernous hemangioma, while on EPI, the corresponding figures were 13.84+/-3.02 and45.44+/-11.21. CONCLUSION: In detecting focal hepatic mass, the sensitivity of EPI and breath-hold fast T2WI arecomparable; for the diagnosis of small HCC and cavernous hemangioma, EPI can provide additional information.

Multishot Echoplanar MR Imaging of the Female Pelvis: Comparison with T2 weighted Fast Spin Echo Imaging

PURPOSE: To compare the usefulness of multishot echoplanar imaging (EPI) with T2-weighted fast spin-echoimaging (FSE) for the evaluation of female pelvic organs and pathologic conditions. MATERIALS AND METHODS:Twenty-nine patients with pelvic lesion underwent MR imaging (GE Medical Systems) using a pelvic array coil (GEMedical Systems). Axial EPI (TR/TE=2,000/80, 6mm slice thickness, 2.5mm gap, multishot 16) and T2-weighted FSE(TR/TE=3,400/117, 5mm slice thickness, 1.5mm gap, ETL=12) were obtained. Overall image quality, the parametrialvenous plexus, anatomy of the uterine zone and outer margin, identification of the ovaries, pelvic pathologiccondition, and frequency of artifact, as seen on EPI and FSE imaging were reviewed separately by two radiologists. RESULTS: For overall imaging quality, EPI was superior to FSE in 14% of patients(4/29), equal in 24%(7/29), andinferior in 62%(18/29). For delineation of the parametrial venous plexus, EPI was superior to FSE in 79%(23/29).For uterine zonal anatomy and the outer margin, EPI was inferior to FSE in 55%(16/29) and in 45%(13/29),respectively. On EPI, visualization of the ovary was rated superior to FSE in 0%(0/9), equal in 52%(15/29), andinferior in 48%(14/29). Conspicuity of pelvic pathologic lesions was superior in 14%(4/29), equal in 52%(15/29),and inferior in 48%(14/29). Image distortion and susceptibility artifacts were seen on EPI in six cases, while onFSE motion artifacts were seen in two cases. CONCLUSIONS: As EPI is inferior to FSE in overall image quality,delineation of the normal anatomy of pelvic organs and conspicuity of pelvic lesions, it cannot replace FSE forimaging the female pelvis. However, because EPI reduces imaging time, further technical progress in this area maystimulate the use of ultrafast imaging of the femal pelvis.

MRCP Using Breath-hold HASTE Sequence: Comparison of Maximum Intensity Projection Image with Single Slice Acquisition Image

PURPOSE: To compare the usefulness of single-slice acquisition imaging and conventional maximum intensity projection imaging, as employed in magnetic resonance cholangiopancreatography (MRCP) using the Half-Fourier Acquisition Single Shot Turbo Spin-Echo(HASTE) sequence. MATERIALS AND METHODS: Five healthy volunteers underwent MRCP using the HASTE sequence on a 1.5T MR unit. Two data acquisition techniques were used : 1) single slice acquisition, with 20 mm slice thickness (imaging time, 2 sec), 2) multi-slice acquisition, with 5 mm slice thickness (imaging time, 19 sec), followed by maximum intensity projection reconstruction. Two radiologists independently evaluated the MRCP images obtained using these two techniques; based on the depiction by each of ten anatomic structures, their quality was graded as excellent (3 points), good (2 points), fair(1 point) or poor(0). Mean scores were totalled, and to compare the quality of the two techniques, these scores were compared. Data was statistically analyzed using the paired student t-test. RESULTS: There was no difference in bile duct image quality between the two techniques. The pancreatic duct was more conspicuous on single-slice (mean score, 1.94) than on maximum intensity projection imaging (mean score, 0.7). The sum of the mean scores of single-slice imaging was 18.75, and that of maximum intensity projection imaging was 14.7 (p=0.42); the general difference between the two techniques was thus statistically insignificant. CONCLUSION: Compared with maximum intensity projection imaging, single-slice imaging had a distinct advantage : acquisition time was short (within 2 sec), thus motion artifacts could be avoided, and there was no need for post-processing. There is a close and direct connection between the avoidance of motion artifact and short acquisition time, but lack of need for post-processing is independent. On single-slice images, the pancreatic duct was more conspicuous than on maximum intensity projection images. The former can therefore be used with patients who experience respiratory difficulty or are suspected to be suffering from disease of the pancreotic duct.

The imaging display of aortic dissection in T1W/TFE sequence of MRI / 西安交通大学学报(医学版)

Objective To examine aortic dissection by using T1W/TFE sequence and to observe the imaging characteristics of aortic dissection in T1W/TFE sequence. Methods Twenty patients confirmed as aortic dissection by CT and ultrasound received MRI scanning of T1W/TFE sequence on inclined sagittal and SE sequence on transaxial at Philips Gyroscan 1.5 MR imager. The signal changes of aortic dissection in T1W/TFE sequence were observed. Results In T1W/TFE sequence, we observed not only an intimal flap, a double lumen and range of aortic dissection, but also the site of intimal tear and thrombus in the false lumen. Conclusion By using T1W/TFE sequence we obtained the high quality image of aortic dissection and high contrast of imaging. Combined with SE sequence , T1W/TFE sequence can provide reliable information for analyzing and curing aortic dissection in clinic.