Usefulness of MR Cholangiopancreatography after Intravenous Morphine Administration

PURPOSE: We wanted to assess the usefulness of MRCP after intravenous morphine administration in the evaluation of the hepatopancreatic pancreatico-biliary ductal system. MATERIALS AND METHODS: We studied 15 patients who were suspected of having disease of hepatopancreatic ductal system and they did not have any obstructive lesion on ultrasonography and/or CT. MRCP was acquired before and after morphine administration (0.04 mg/kg, intravenously). Three radiologists scored the quality of the images of the anatomic structures in the hepatopancreatic ductal system. We directly compared the quality of the images obtained with using the two methods and the improvement of the artifacts by pulsatile vascular compression. RESULTS: The MRCP images obtained after intravenous morphine administration were better than those obtained before morphine administration for visualizing the hepatopancreatic ductal system. On direct comparison, the MRCP images obtained after morphine administration were better in 12 cases, equivocal in two cases, and the images before morphine administration were better in only one case. In three patients, MRCP before morphine injection showed signal loss at the duct across the pulsatile hepatic artery. In two of three patients, MRCP after morphine injection showed no signal loss in this ductal area. CONCLUSION: MRCP after intravenous morphine administration enables physicians to see the hepatopancreatic ductal system significantly better and the artifacts caused by pulsation of the hepatic artery can be avoided.

PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) and EPI Diffusion-weighted MR Imaging at 3.0T: Pontine Magnetic Susceptibility Artifacts Depend on Pneumatization of the Sphenoid Sinus

PURPOSE: In the case of well pneumatized sphenoid sinus, magnetic susceptibility artifact can be visualized at the brainstem and especially at the pons on echo-planar imaging (EPI) diffusion-weighted imaging. Fast spin-echo periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) is a novel imaging method that can reduce these artifacts. In 3.0T MR, we first evaluate the degree of the relationship of pneumatization of the sphenoid sinus with the occurrence of magnetic susceptibility artifacts (MSA) on the echo planar imaging (EPI) diffusion-weighted imaging (DWI), and we evaluated using PROPELLER-DWI for cancellation of MSAs of the pons in the patients who had MSAs on the EPI-DWI. MATERIALS AND METHODS: Sixty subjects (mean age: 58 years old and there were 30 men) who were classified according to the two types of sphenoid sinus underwent EPI-DWI. The two types of sphenoid sinus were classified by the degree of pneumatization on the sagittal T2-weighted image. The type-1 sphenoid sinus was 0% to less than 50% aeration of the bony sellar floor, and type-2 was 50% or more aeration of the boney sellar floor. Each of 10 subjects (n=20/60, mean age: 53) of the two types had PROPELLER and EPI-DWI performed simultaneously. We first evaluated the absence or presence of MSAs at the pons in the two types, and we compared EPI and PROPELLER-DWI in the subjects who underwent the two MR sequences simultaneously. We used 3.0T MR (Signa VHi, GE, MW, U.S.A.) with a standard head coil. All the MR images were interpreted by one neuroradiologiest. RESULTS: For the type-1, two (6.7%) cases had MSAs and 28 (93.7%) cases did not have MSAs on the EPI-DWI. For the type-2, twenty-seven (90%) cases had MSAs and 3 (10%) cases did not have MSAs on the EPI-DWI. The degree of pneumatization of the sphenoid sinus was related with the occurrence of MSAs of the pons, according to the chi-square test (p=0.000). All twenty cases who had PROPELLER-DWI performed had no MASs at the pons regardless of the type of sphenoid sinus. But all ten cases of type-2 produced MASs on the EPI-DWIs CONCLUSION: For EPI-DWI, a well aerated sphenoid sinus can induce MASs at the pons, and we should recognize this phenomenon to differentiate it from true infarcted lesion. PROPELLER DWI can be an optional tool to use for canceling this artifact.

The Pitfalls of the Magnetic Resonance Cholangio-Pancreatography the Diagnosis of Biliary Stones

PURPOSE: To determine the incidence of flow artifact and vascular compression, phenomena that mimic biliary stone disease at magnetic resonance cholangio pancreatography (MRCP). MATERIALS AND METHODS: In 160 patients who underwent MRCP, the prescence and location of flow artifact were determined. The signal intensity of flow artifacts was chassifieded as either higher than renal cortical density (group I), the same as renal cortical density (group II), the same as hepatic density (group III), or the same as vascular density (group IV). Correlation between flow artifact and the largest diameter of the extrahepatic duct (EHD) was statistically evaluated, and the location of vascular compression in the biliary system and causative vessels was also determined. RESULTS: At MRCP, flow artifacts were observed in 81 patients (76.4%). Forty-five (42.5%) were classified as group I, 15 (14.2%) as group II, 18 (17.0%) as group III, and three (2.8%) as group IV. They were located in the common bile duct (78.3%), common hepatic duct (70.0%), or intrahepatic duct (29.2%) or at the cystic duct insertion site (7.5%). In patients in whom a flow artifact was not apparent, the diameter of the EHD was 7.1mm; in those with an artifact, this diameter was 11.3 mm. The mean diameter of the EHD was greater in groups II, III and IV (11.4 mm) than in group I (9.8 mm). Vascular compression was demonstrated in 21 patients (19.8%), occurring in the common hepatic duct in 8.5%, the left intrahepatic duct in 8.5%, the common bile duct in 1.9%, and the right intrahepatic duct in 0.9%. Causative vessels were the right hepatic artery (12.5%), left hepatic artery (5.7%), and branches of the gastroduodenal artery (1.9%). CONCLUSION: As the extrahepatic duct is wide, a flow artifact appears and signal intensity decreases. In particular, flow artifacts with a signal intensity of grade III or IV, occuring in 19.8% of patients, mimicked biliary stones at MRCP. The presence of a flow artifact and vascular compression, which mimic biliary stone, therefore be carefully interpreted.

High Signal Intensity on T1-Weighted MR Image Related to Vacuum Cleft in the Intervertebral Disk: Clinical and Phantom Study

PURPOSE: To determine the possible mechanism by which an area of high signal intensity appears on T1-weighted MR images adjacent to a vacuum cleft in intervertebral disks. MATERIALS AND METHODS: We analyzed a total of 14 disks in nine patients in whom a vacuum cleft with T1-signal hyperintensity was observed. Lesions were present from T11-12 to L5-S1 using a 1.5-T whole-body imager, sagittal spine-echo T1-weighted and gradient-echo images (flip angle, 20 'and 60 ) were obtained. In order to identify the vacuum cleft, using plain radiographs in all patients and CT scans in two were also obtained. A 3% agar-gel block containing empty slits to form a magnetic susceptibility difference, a phantom was designed. The air spaces were 1.6 mm in thickness, 25 mm in width, and 20 to 25 mm in depth with 1.6-mm spacing. RESULTS: In all patients, vacuum clefts were confirmed by plain radiographs and CT scans. At the level containing air, T1-weighted images (both spin-echo and gradient-echo) showed a signal void resulting from the intervertebral disk vacuum cleft. A hyperintense band adjacent to the vacuum cleft was, however, observed. A gradient-echo image with a 60 'flip angle showed a brighter signal intensity than one with a 20 'angle. Our phantom study gave the same results. CONCLUSION: The magnetic susceptibility artifact may be responsible for the T1-signal hyperintensity observed adjacent to the vacuum cleft in intervertebral disks. In addition, in order to generate signal hyperintensity, the desiccating disk material must contain a certain amount of water molecules.

High Signal Intensity on T1-Weighted MR Image Related to Vacuum Cleft in the Intervertebral Disk: Clinical and Phantom Study

PURPOSE: To determine the possible mechanism by which an area of high signal intensity appears on T1-weighted MR images adjacent to a vacuum cleft in intervertebral disks. MATERIALS AND METHODS: We analyzed a total of 14 disks in nine patients in whom a vacuum cleft with T1-signal hyperintensity was observed. Lesions were present from T11-12 to L5-S1 using a 1.5-T whole-body imager, sagittal spine-echo T1-weighted and gradient-echo images (flip angle, 20 'and 60 ) were obtained. In order to identify the vacuum cleft, using plain radiographs in all patients and CT scans in two were also obtained. A 3% agar-gel block containing empty slits to form a magnetic susceptibility difference, a phantom was designed. The air spaces were 1.6 mm in thickness, 25 mm in width, and 20 to 25 mm in depth with 1.6-mm spacing. RESULTS: In all patients, vacuum clefts were confirmed by plain radiographs and CT scans. At the level containing air, T1-weighted images (both spin-echo and gradient-echo) showed a signal void resulting from the intervertebral disk vacuum cleft. A hyperintense band adjacent to the vacuum cleft was, however, observed. A gradient-echo image with a 60 'flip angle showed a brighter signal intensity than one with a 20 'angle. Our phantom study gave the same results. CONCLUSION: The magnetic susceptibility artifact may be responsible for the T1-signal hyperintensity observed adjacent to the vacuum cleft in intervertebral disks. In addition, in order to generate signal hyperintensity, the desiccating disk material must contain a certain amount of water molecules.

Effect of Angulation between Aorta and Renal Artery on Signal Void of Proximal Renal Artery on MR Angiography:Phantom Study

PURPOSE: To determine the effect of anglulation between aorta the and renal artery on signal loss in theproximal renal artery, as seen on magnetic resonance angiography by phantom study using a pulsatile flow model. MATERIALS AND METHODS: Three phantoms of aorta and renal artery with angulation of 90 degree, 60 degree, and 30 degree wereobtained. Pulsatile recirculating flow (44%W/W glycerin, 60bpm) was used for MR angiography. First, axial 3D-TOFimages were obtained and reconstructed. MIP images were analyzed for the presence, area, and location of signalloss. 2D-PC images were obtained perpendicularly to the renal artery at a distance of 0, 4, 8 and 12mm from theostium. To calculate mean signal intensity of the renal artery, a ROI was drawn on 2D-PC images. To correlatesignal loss in 3D-TOF images with signal decrease in 2D-PC, we analyzed changes in signal intensity during onepulse cycle according to change of angulation and distance from the ostium of the renal artery by the calculatedvalues of relative signal decrease and ratio of signal decrease. RESULTS: A signal loss was observed up to 4mmfrom the ostium of the renal artery only in the case of the 90 degree phantom. Because the signal intensity measured inthe 2D-PC image of the 90 degree phantom was higher than that of the 60 degree phantom the signal loss observed in the3D-TOF images of the 90 degree phantom could not be explained by the magnitude of measured signal intensity alone.Relative signal decrease only at a distance of 0 and 4mm in the 90 degree phantom was evenly increased through a pulsecycle and the ratio of signal decrease at the same location was more than 50%. In contrast to the results of the90 degree phantom, those of 60 degree and 30 degree showed decreased of signal intensity mainly during the diastolic phase.CONCLUSION: Signal loss should become apparent at a certain angle between 60 degree and 90 degree. Decreased signalintensity causing signal loss in 3D-TOF was maintained throughout the systolic and diastolic phase of a pulsatilecycle and correlated with the ratio of signal decrease.

Correlation of Laminated MR Appearance of Artcular Cartilage with Histology

PURPOSE: To determine the correlation of laminae of different signal intensities (SI) of articular cartilage,as seen on magnetic resonance (MR) imaging with histologic layes, using artificially constructed landmarks. MATERIALS AND METHODS: For a landmark that can exactly correlate the cartilage specimen with the MR image, five'V'-shaped markings of different depths were made on the surface of bovine patella. Both T1-weighted (TR/TE :300/14) and FSE T2-weighted images (TR/TE : 2000/53) were obtained on a 1.5T system with high gradient echostrength (25mT/m) and a voxel size of 78x78x2000 micrometer. Images were obtained with 1) changed frequency-encodingdirections on T1-weighted study, and 2) changed readout gradient strength (x2, x1/2) on T2-weighted sequence.Raw image data were transferred to a workstation and signal intensity profile was generated for each image. 1 : 1correlation of histologic specimens and MR images was performed. RESULTS: Line Profile through the cartilageshowed few peaks, suggesting changes in signal intensity profile in the cartilage. On the basis of artificiallandmarks, the histologic zone was accurately identified. The histologic tangential and transitional zonescorrelated with superficial high SI on T1WI, as well as high and low SII on T2WI. On T1WI, the radial zonecorrelated with a lamina of intermediate SI, and on T2WI, with a lamina for which SI gradually decreased from highto low. Additional well-defined low and intermediate SI bands were noted on bovine T1WI in the lower radial zone.In both T1 and T2 studies, calcified cartilage layers were of low SI. On T1-weighted study, changes in thedirection of frequency gradient did not lead to changes in the laminae. The alteration of readout gradientstrengths did not result in an inversely proportional difference in the thickness of the laminae. These becamemore distinct thus ruling out chemical shift and susceptibility artifacts. CONCLUSION: The laminated appearanceof articular cartilage, as seen on spin echo and fast spin-echo MR images, correlated with histologic layersrather than susceptibility or chemical shift artifacts.

Artifacts in MR Angiography of the Intracranial Vessels Using the 3D TOF and 3D PC Techniques

PURPOSE: To classify artifacts and to assess their frequency in magnetic resonance angiography of intracranial vessels using three-dimensional time-of-flight and phase-contrast techniques. MATERIALS AND METHODS: One hundred and eleven patients with suspected cerebrovascular disease were imaged on a 1.5T superconducting magnetic, resonance machine employing three-dimensional time-of-flight and phase-contrast magnetic resonance angiographic techniques. We retrospectively reviewed the artifacts in three-dimensional time-of-flight and phase-contrast magnetic resonance angiography of the intracranial circulatory system, comparing them with routine spin-echo magnetic resonance images and magnetic resonance angiography source images, and partially with conventional angiography. RESULTS: Artifacts in magnetic resonance angiography were classified as flow-related, and flow-unrelated, by patient, hardware, magnetic resonance angiography acquisition and postprocessing techniques. Type and frequency of flow-related artifacts included saturation artifact (100%), dephasing artifact(100%), phase-encoding ghost artifact (97%), turbulence artifact (14%) and flow displacement artifact (5%) on three-dimensional time-of-flight and phase-contrast magnetic resonance angiography, and phase aliasing artifact(2%) on three-dimensional phase-contrast magnetic resonance angiography. Type and frequency of flow-unrelated artifacts included stair-step artifact (100%) by three-dimensional reconstruction process, magnetic susceptibility artifact by carotid canal (69%) and metal (4%), maximum intensity projection artifact (30%) by maximum intensity projection algorithm, and motion artifact by respiration (20%) and voluntary movement(8%); these were seen on both time-of-flight and phase-contrast magnetic resonance angiography. Paramagnetic substance artifact by fat and paranasal sinus mucosa (100%), hematoma(14%) and gadolinium (5%) were seen on time-of-flight magnetic resonance angiography. CONCLUSION: In three-dimensional time-of-flight and phase-contrast magnetic resonance angiography, being familiar with the common artifacts and with their physical principles helps avoid misinterpretation of magnetic resonance angiography. An understanding of the causes of such artifacts will enable the radiologist to make rational changes in imaging technique and eliminate or reduce the effects of artifacts on magnetic resonance angiography.