Enteric MRI contrast agents: comparative study of five potential agents in humans.

We compared the effectiveness of 1 mM Geritol, 12% corn oil emulsion, Kaolin-pectin, single contrast oral barium sulfate, and effervescent granules as enteric magnetic resonance imaging (MRI) contrast agents. Five volunteers were recruited. Each volunteer ingested for examinations, separated by at least one week, either 500 ml of each of the liquid preparations or two packets of the CO2 granules (producing 400 ml of CO2 per packet). Abdominal MR images were then obtained using a 1.5 T Magnetom imager and SE 550/22, SE 2000/45/90 and FISP 40/18/40 degrees pulse sequences. The oil emulsions were best tolerated. Barium sulfate caused the greatest amount of nausea, followed by Geritol and Kaolin-pectin. With FISP 40/18/40 degrees, 60%-80% of the small bowel was well delineated using oil emulsion, Kaolin-pectin, or barium sulfate. We conclude that oil emulsion was by far the best enteric MR contrast agent in our study. Good delineation of the small bowel and pancreas can be achieved using oil emulsion and gradient echo pulse sequences. The lack of side-effects and the excellent taste make it highly acceptable to human subjects.     

MRI with superparamagnetic iron oxide: efficacy in the detection and characterization of focal hepatic lesions

The purpose of this study was to evaluate the potential of superparamagnetic iron oxide particles (SPIO) as tissue specific contrast agent in magnetic resonance (MR) imaging in detection and characterization of focal hepatic lesions. We investigated 45 patients with focal hepatic lesions. T1-weighted SE (TR 650/TE 15 ms) and T2-weighted SE (TR 2015-2030/TE 45 and 90 ms) unenhanced images were obtained. After SPIO application we performed T1-weighted images with and T2-weighted images with and without fat suppression using the same image parameters. Liver signal intensity decreased by 74% (min 47%, max 83%) on T2-weighted images after application of the contrast agent. Benign lesions (FNH, adenoma) showed an average signal drop of 40% (min 20%, max 47%) whereas malignant lesions showed no significant change of signal intensity on post-contrast images. The mean tumor-to-liver contrast-to-noise ratio (C/N) was improved in all post-contrast sequences irrespective of the lesion type. An additional increase of tumor-to-liver contrast by use of fat suppression technique could be established in the slightly T2-weighted sequence (TE 45 ms). In metastases, divided in different size groups, we could determine a significant size relation of tumor-to-liver C/N. After SPIO application the number of detected lesions increased distinctly, especially small foci are more easily demonstrated. SPIO particles are a efficacious contrast agent for MR examinations of the liver. For tumor characterization T1- and T2-weighted pre- and post-contrast images are necessary. The T1-weighted sequences are helpful to differentiate benign lesions such as cysts and hemangiomas from malignant lesions. Detection and differential diagnoses of hepatic lesions are improved by use of the SPIO-particles.     

Barium sulfate suspension as a negative oral MRI contrast agent: in vitro and human optimization studies

In vitro proton spectroscopy with line-width measurements and MR imaging were performed on various concentrations of commercially available single contrast (SC), double contrast, oral and rectal barium sulfate suspensions, as well as potassium sulfate, barium chloride, barium hydroxide, and 97% pure barium sulfate suspensions. Approximately 500 ml of 20%, 40%, 60%, and 70% w/w suspensions of SC oral barium sulfate suspensions were administered to four normal volunteers, respectively, and MR images were obtained at both 1.5 T and 0.15 T. Subsequently, 500 ml of 60% w/w suspensions of SC oral barium sulfate suspensions were administered to five normal volunteers and imaged at 1.5 T. All of the inert suspensions produced line-width broadening but the SC oral barium sulfate suspension at 50% and 70% stayed in suspension even after hours of standing undisturbed. As much as 80% of the small bowel and the entire colon were well visualized using the combination of 60% or 70% w/w SC barium sulfate suspensions with SE 550/22 and FISP pulse sequences. The effect was less at 0.15 T and also with the SE 2000/45/90 pulse sequences. We conclude that barium sulfate suspensions are useful as oral MRI contrast agents.     

Experimental cerebral infarction in the rat: utility of Gd-DOTA for MR imaging

Nineteen rats presenting a very small (about 2-mm diameter), superficial cerebral infarction were studied with MR-imaging (1.89 Tesla) before and after injection of Gd-DOTA. Fifteen rats examined 1 or 2 hr, and 2, 3, 4, 5, 7, or 10 days after lesion induction, received 0.5 mmol Gd-DOTA/kg body weight. Four other rats presenting a 4-day-old lesion, received 0.1, 0.2, or 0.6 mmol Gd-DOTA/kg. Each rat underwent one imaging study comprising T2-weighted spin-echo (SE) images (3000/100) with subsequent injection of Gd-DOTA followed by 12 consecutive series of T1-weighted SE images (320/40), each taking 6 min. Using 0.5 mmol Gd-DOTA/kg, early (immediate) and long-lasting (more than 1 hour) visualization of lesions of varying age (1 hr to up to 10 days) was possible and at appropriate time intervals after injection, the visualization of the lesion was clearer and more complete than with T2-weighted images. Even in the rats studied with smaller doses of the contrast agent (0.1 or 0.2 mmol/kg), postcontrast T1-weighted images provided superior delineation of the lesions as compared to T2-weighted images.     

Vegetable oil as an MR contrast agent for rectal applications

The purpose of the study was to evaluate the feasibility of pure vegetable oil as an MR contrast agent for rectal applications. The hypothesis was that vegetable oil highlights the lumen of the rectum after rectal application as a positive contrast medium and offers additional contrast qualities using fat suppression techniques. Eleven MRI examinations were performed on 11 subjects (five healthy volunteers, all males, mean age 35 yr; and six patients, three males, three females, mean age 49 yr). Peanut oil, 200 ml, was applied rectally. In addition, 0.1 mmol/kg GD-DTPA was administered intravenously to the six patients only. Conventional T₁-weighted SE sequences and and T₁-weighted SE images with fat suppression were obtained. Criteria for image evaluation were: overall image quality; uniformity of contrast distribution; chemical shift artifact; and delineation of the rectal wall. Side effects were assessed. There were no complaints reported by the 11 subjects. The image quality was sufficient in all studies. In all five of the volunteers and five of the six patients, the distribution of oil was uniform. Chemical shift artifacts did not deteriorate image quality. After rectal application of vegetable oil, the delineation of the rectal wall was sufficient with and without fat suppression techniques. Vegetable oil highlights the lumen of the rectum in MRI studies and offers additional contrast qualities with fat suppression techniques, acting as a positive as well as a negative contrast agent, depending on the chosen sequence.     

High field imaging of the normal pancreas

Fifty MR scans conducted at 1.5 T were evaluated to assess how well the pancreas could be identified. A total of 128 sets of images were reviewed. The pancreatic head was identified in 81%, 82% and 74% of scans with T1, intermediate and T2-weighting, respectively. The body was identified in 100%, 96% and 70% and tail in 96%, 87% and 54% on those respective sequences. Relative contrast was calculated between pancreas and: liver, spleen, muscle, fat, stomach and small bowel. The variability seen in contrast compared to stomach and small bowel suggests that consistent MR visualization of the pancreas will probably necessitate the use of an oral contrast agent.     

Macroscopic tumor volume of malignant glioma determined by contrast-enhanced magnetic resonance imaging with and without magnetization transfer contrast

The purposes of this study were to compare the conspicuity and lesion volume of contrast-enhancing macroscopic malignant glioma determined by postcontrast magnetic resonance (MR) imaging with and without magnetization transfer (MT) saturation, and to discuss possible implications for radiotherapy planning. Nineteen patients (age 24–60 years) with histologically proven malignant glioma were prospectively examined by MR imaging. After the administration of gadolinium dimeglumine (0.1 mmol/kg body weight), the lesions were imaged with an MT-weighted FLASH (fast, low-angle shot) pulse sequence and with a conventional T₁-weighted spin-echo (SE) sequence without MT saturation. The mean tumor volumes of gliomas measured on MT-weighted FLASH images were significantly (p < .01) larger than those obtained from T₁-weighted SE images (45 ± 15 cm³ vs. 33 ± 10 cm³). The mean contrast-to-noise ratio of enhancing lesions on MT-weighted FLASH was 48 ± 14 compared with 30 ± 14 on SE images, representing a significant (p < .01) improvement. We conclude that the volume of contrast enhancement of malignant glioma identified on MT-weighted FLASH images represents the area of disrupted blood-brain barrier. If this volume of subtle contrast enhancement is caused by tumor infiltration and represents the boost target volume for stereotactic radiosurgery or brachytherapy, MT-weighted FLASH images would be better than T₁-weighted SE images to define these volumes. These improved delineation of areas at highest risk for recurrence following radiation therapy should enhance the efficacy of treatment planning for high-boost therapy.     

Dual-echo breathhold T(2)-weighted fast spin echo MR imaging of liver lesions

The purpose of this study was to develop a multi-shot dual-echo breathhold fast spin echo technique (DFSE) and compare it with conventional spin echo (T2SE) for T(2)-weighted MR imaging of liver lesions. The DFSE acquisition (EffTE1/EffTE2/TR = 66/143/2100 ms) imaged 5 sections per 17 s breathhold. T2SE imaging (TE1/TE2/TR = 60/120/2500 ms) required 16:55 (min:s) for 14 sections. Both techniques used a receive-only phased-array abdominal multicoil and provided 192 x 256 effective resolution. The results showed first and second echo relative DFSE/T2SE contrast values for 27 representative lesions (15 consecutive patients) were 1.08 +/- 0.05 and 1.16 +/- 0.09 (mean +/- STD mean), respectively. Corresponding CNR values were 1.12 +/- 0.09 and 0.97 +/- 0.12. Overall DFSE was comparable-to-superior to T2SE for lesion sizing and image artifact. DFSE lesion detection was inferior to T2SE's in several patient studies because of decreased conspicuity of lesions located near multicoil edges and because of poor breathhold-to-breathhold reproducibility and lack of breathholding. However both DFSE (and T2SE) provided lesion detection rated to be of diagnostic quality for all patient studies. In conclusion, we found that DFSE provides diagnostically useful dual-echo T(2)-weighted MR liver images in a greatly decreased acquisition time.     

Comparison of T1-weighted spin-echo and 3D T1-weighted multi-shot Echo Planar pulse sequences in imaging the brain at it.

The purpose of this study was to evaluate the ability of three dimensional T1-weighted multi-shot Echo Planar Imaging (3D T1w EPI) MR pulse sequence to provide comparable to T1w Spin Echo (SE) results in various diseases of the brain, during shorter acquisition times. Thirty-six patients (aged 30-74 years) with various indications were included in the study. All examinations were performed with a 1T MR scanner with a maximum gradient strength of 15 mT/m. The SE sequence lasted 3 min 50s and the 3D T1w EPI 59s. The quantitative analysis included number of enhancing lesions, signal-to-noise ratio of the enhancing lesions and contrast-to-noise ratio (CNR) between enhancing lesions and white matter in both sequences before and after i.v. administration of 0.1 mmol/kg gadopentetate dimeglumine. In addition, the percentage increase of enhancement was measured in each lesion of each sequence. The qualitative analysis included a) conspicuity of the lesions and b) presence of artifacts. The T1w SE sequence was significantly better compared to 3D T1w EPI in all quantitative measurements with the exception of CNR of enhancing lesions before contrast administration and the percentage enhancement. The conspicuity of the lesions did not differ between the two sequences. The EPI sequence presented with significantly more artifacts. We conclude that the 3D T1w EPI sequence could not be used instead of the conventional T1w SE, in routine imaging of the brain. Its overall diagnostic capability, could be useful only in uncooperative patients.     

Liver imaging at 1.5 tesla: pulse sequence optimization based on improved measurement of tissue relaxation times

In order to predict the most sensitive MR imaging sequence for detecting liver metastases at 1.5 T, in vivo measurements of T1 and T2 relaxation times and proton density were obtained using multipoint techniques. Based on these measurements, two-dimensional contrast contour plots were constructed demonstrating signal intensity contrast between hepatic lesions and surrounding liver parenchyma for different pulse sequences and pulse timing parameters. The data predict that inversion recovery spin echo (IRSE) imaging should yield the greatest contrast between liver metastases and liver parenchyma at 1.5 T, followed by short tau inversion recovery (STIR) and spin-echo (SE) pulse sequences. T2-weighted SE images provided greater liver/lesion contrast than T1-weighted SE pulse sequences. Calculated T1, T2, and proton density values of the spleen were similar to those of hepatic metastatic lesions, indicating that the signal intensity of the spleen may be used as an internal standard to predict the signal intensity of hepatic metastases on T1- and T2-weighted images at 1.5 T.     

Inhalation MR lymphography: A new method for selective enhancement of the lung hilar and mediastinal lymph nodes

On MR lymphography, a new approach to the lung hilar and mediastinal nodes was developed in an animal model. Five rabbits were made to inhale iron colloid (cideferron) that was nebulized to aerosol. Two days after inhalation of the agent, the mediastinal lymph nodes decreased in signal on SE 2000/30 and SE 2000/60 images and proved to have iron on histological evaluation, whereas the popliteal nodes did not have any iron. Experimental results indicate that inhalational administration can deliver the agent to the pulmonary lymphatic system and has the potential of lung hilar and mediastinal MR lymphography.     

Methods for the systematic investigation of gastrointestinal contrast media for MRI: evaluation of intestinal distribution by radiographic monitoring

Comparison of the effectiveness of various gastrointestinal (GI) contrast agents for magnetic resonance (MR) imaging is often complicated by varying amounts intraluminal filling with the orally administered agents. To achieve more uniform and reproducible imaging results with GI contrast agents for MR imaging (GICMR), we evaluated a radiographic method for monitoring intraluminal filling and distribution. Solutions of Mn-DPDP (2 mM), to which a small amount of barium sulfate (6 wt/vol%) was added, were administered orally to dogs. Gastric emptying and small bowel transit were monitored fluoroscopically. MR imaging was performed either 1) at a fixed time after administration of the contrast agent or 2) at a variable interval when the contrast agent was observed fluoroscopically to be in the terminal ileum. When initiation of MR imaging was guided by fluoroscopic monitoring of intestinal contrast distribution, uniform and reproducible intestinal contrast enhancement by GICMR was achieved. However, when MR imaging was performed at a fixed time interval after oral administration, non-uniform and variable GI visualization was obtained, and this corresponded to the variable intestinal distribution observed fluoroscopically. We conclude that reproducible intestinal filling with orally administered contrast agents can be accomplished with a radiographic monitoring technique, and this promotes more consistent GI visualization on MR images. Such standardized and reproducible methods are necessary for studies in which the effectiveness of GI contrast media for MR imaging is evaluated and compared.     

Evaluation of STIR imaging as a complement to spin-echo MR and CT of the porta hepatis/hepatoduodenal ligament

Short TI inversion-recovery (STIR) imaging provides specific advantages over standard spin-echo (SE) MR sequences by producing additive effects of T1 and T2 brightening of pathology and suppression of the signal from surrounding fat. We retrospectively evaluated 12 patients with abnormalities, primarily neoplastic, of the porta hepatis/hepatoduodenal ligament (PH/HdL) with CT and MR imaging, including SE and STIR imaging. Masses on CT were of slightly decreased density compared to liver and seen in contrast to surrounding fat in the PH/HdL region. On MR, T1-weighted images provided comparable anatomic detail to CT, with masses clearly distinguished from surrounding fat due to the low signal intensity of masses as compared to fat. T2-weighted images clearly depicted intrahepatic lesions because of their high signal intensity relative to liver. Increased signal in extrahepatic lesions made them less distinctly seen from surrounding fat. STIR images best demonstrated tumor relative to fat. In six cases, CT was equivalent in demonstrating pathology to the best MR sequence. At least one MR sequence demonstrated pathology better than CT in 6 of 12 cases. In five of these six cases, the STIR sequence was better than CT. Thus, MR, particularly STIR imaging, provides a useful technique in imaging of PH/HdL pathology.     

Small hepatocellular carcinomas in cirrhosis: differences in contrast enhancement effects between helical CT and MR imaging during multiphasic dynamic imaging

PURPOSE: The purpose of this study was to evaluate differences in the degrees of contrast enhancement effects of small hepatocellular carcinomas (HCCs) in patients with cirrhosis between helical computed tomography (CT) and magnetic resonance (MR) imaging during multiphasic contrast-enhanced dynamic imaging and to determine the diagnostic value of MR imaging especially in assessing hypovascular HCCs detected as hypoattenuating nodules on late-phase CT. SUBJECTS AND METHODS: This study included 64 small HCCs (<3 cm in diameter) in 40 patients with chronic hepatitis or cirrhosis who underwent multiphasic (arterial, portal and late phases) contrast-enhanced dynamic helical CT and MR imaging. The contrast enhancement patterns of each lesion in the arterial and late phases were evaluated by two radiologists experienced in liver MR imaging and categorized as one of five grades (1=hypoattenuated/hypointense; 2=slightly hypoattenuated/hypointense; 3=isoattenuated/isointense; 4=slightly hyperattenuated/hyperintense; 5=hyperattenuated/hyperintense), compared with the surrounding liver parenchyma. RESULT: Forty-three (67%) of 64 lesions showed Grade 4 (n=24) or Grade 5 (n=19) enhancement on arterial-phase CT, while 51 (80%) of 64 lesions showed Grade 4 (n=20) or Grade 5 (n=31) enhancement on arterial-phase MR imaging, indicating hypervascular HCCs. The grading score of hypervascular HCCs on arterial-phase MR imaging (mean: 4.61) was significantly (P<.01) higher than that for hypervascular HCCs on arterial-phase CT (mean: 4.20), showing better detection of the hypervascularity (arterial enhancement) of the lesion on arterial-phase MR imaging. Regarding hypovascular HCCs, all (100%) of 21 hypovascular HCCs on CT showed Grade 1 (n=10) or Grade 2 (n=11) enhancement on late-phase CT, seen as hypoattenuation. In contrast, 8 (62%) of 13 hypovascular HCCs on MR imaging showed Grade 1 (n=1) or Grade 2 (n=7) enhancement on late-phase MR imaging, seen as hypointensity. Grading scores of hypovascular HCCs on late-phase images were significantly (P<.001) lower on CT than on MR imaging (mean score: 1.52 vs. 2.31), indicating better washout effects for hypovascular HCCs on late-phase CT. CONCLUSION: The washout effects for small HCCs on late-phase MR imaging were inferior to those for small HCCs on late-phase CT. Especially, hypovascular HCCs demonstrated as hypoattenuating nodules on late-phase CT were often not seen on late-phase MR imaging, requiring careful evaluation of other sequences, including unenhanced T(1)-weighted and T(2)-weighted MR images.     

A functionalized superparamagnetic iron oxide colloid as a receptor directed MR contrast agent.

We have synthesized a surface functionalized superparamagnetic iron oxide colloid whose clearance from the vascular compartment was inhibited by asialofetuin but not fetuin. Unlike other particulate or colloidal magnetic resonance (MR) contrast agents, the agent of the current communication is not withdrawn from the vascular compartment by cells of the macrophage-monocyte phagocytic system, as indicated by its selective increase in hepatic relaxation rates. Because of this we refer to this colloid as a hepatic selective (HS) MR contrast agent. At 20 mumol Fe/kg the HS MR agent darkened MR images of liver. The HS MR agent exhibited no acute toxicity when injected into rats at 1800 mumol Fe/kg. Based on these observations, surface functionalized superparamagnetic iron oxide colloids may be the basis of MR contrast agents internalized by receptor mediated endocytosis generally, and by the asialoglycoprotein receptor in particular.     

Magnetic resonance imaging in hemophilic children: value of gradient echo and contrast-enhanced imaging

The purpose of this study was to determine the value of Gradient Echo imaging for the evaluation of cartilage (3D fatsat) and blood products (2D Hemoflash), and the use of contrast enhanced SE imaging for the evaluation of synovial changes, in comparison to the clinical evaluation of children with hemophilia A. We investigated 21 joints in 16 patients with evidence of hemophilia A (mean age 11.3+/-2.1 years). In all patients, clinical examination, plain film radiographs, and MR evaluation were performed magnetic resonance imaging (MRI) was performed by using sagittal T1 SE and T2 SE images, as well as 3D fatsat GE and 2D GE images. Axial and sagittal T1 weighted SE images were obtained before and after contrast application. Findings from the clinical examination and MR imaging, regarding the evaluation of blood, synovia, and cartilage were compared. Clinical examination revealed evidence of a bleeding episode in 12 joints (57.1%), whereas MRI revealed evidence of blood or blood products in 15 joints (71.4%). Clinical investigations, including bleeding scores, pain scores, and physical examination scores did not correlate with MR findings. Due to the MR findings in 6 of 16 patients, therapeutic management was changed from on demand to prophylactic therapy. MR imaging with gradient echo and contrast-enhanced sequences is more sensitive than clinical examination for the detection of blood products in children with hemophilia. Its ability to demonstrate potentially early stages of cartilage or synovial alterations might assist in therapy planning. Clinical scores might underestimate effects of hemophilia.     

Bowel-related abscesses: MR demonstration preliminary results

The purpose of this study is to describe the appearance of bowel-related abscesses on magnetic resonance (MR) images. Sixteen consecutive patients who had bowel-related abscesses underwent MR examination at 1.5T. MR sequences included T₁-weighted fat-suppressed imaging pre- and post-intravenous gadolinium chelate administration (all patients) and breathing-independent single-shot T₂-weighted half Fourier turbo (fast) spin echo (6 patients). Patients with pelvic abscesses also underwent sagittal imaging with post-gadolinium T₁-weighted images (9 patients) and T₂-weighted turbo (fast) spin echo (8 patients). Abscesses were confirmed by open surgery or surgical drainage (6 patients), percutaneous drainage (8 patients), or combined physical examination, fluoroscopic fistulogram, and clinical follow-up (2 patients). Oval-shaped fluid collections were identified in all of the patients, which ranged in diameter from 2 cm to 18 cm, mean: 8 cm. Abscesses were low to intermediate in signal on T₁-weighted images, heterogenous and moderately high signal on T₂-weighted images, and low signal on post-gadolinium images. A layering effect of lower signal material in the dependent portion of the abscess was noted in abscesses in 6 of 14 patients on T₂-weighted images. Post-gadolinium images demonstrated a definable 3- to 7-mm thick abscess wall, which enhanced substantially with contrast. Definition of the wall was best shown on fat-suppressed images post-gadolinium. Substantial enhancement of surrounding periabscess tissues was demonstrated in all cases and was most clearly defined on fat-suppressed images. Image acquisition in two orthogonal planes was of value to demonstrate that fluid collections were oval, and separate from bowel. Image acquisition in the sagittal plane was useful in the evaluation of pelvic abscesses. The results from this preliminary study show that bowel-related abscesses are demonstrable on MR images using gadolinium-enhanced fat-suppressed T₁-weighted and turbo (fast) spin-echo T₂-weighted sequences. The presence of a thickened, enhancing lesion wall and enhancement of perilesional tissues on T₁-weighted fat-suppressed images were observed in all abscesses. A layering effect of low signal intensity material in the dependent portion of the abscess was an important ancillary feature.     

Utilization of the nephrectomized mouse for determining threshold effects of MRI contrast agents

The tissue concentration of an extravascularly distributed MRI contrast agent required to achieve a 20% change in the MRI signal intensity (SI) of skeletal muscle was determined using radiolabeled gadoteridol administered to nephrectomized mice. This minimal change in the quantified SI was reliably detected qualitatively in the MR muscle images. MR images of muscle were acquired following each intravenous injection of six sequential doses of 0.8 micromol of 153Gd-labeled gadoteridol. A 2.0 T imaging spectrometer and a T1-weighted spin-echo pulse sequence were used to acquire the MR images. After imaging, the injected 153Gd in muscle was measured, and the 153Gd assay results were used to determine the gadoteridol concentration in muscle following each injection. The muscle concentrations of gadoteridol were then correlated to the quantified enhanced MR SI of muscle. Using the 20% factor, it was concluded that the amount of gadoteridol necessary to achieve a reliable change in the SI of muscle was 33+/-10 nmol/g-skeletal muscle.     

Improved sensitivity of MRI in multiple sclerosis by use of extensive standardized procedures

The relative value of two different MRI procedures for the assessment of infratentorial extension in multiple sclerosis (MS) was studied. Multislice spin-echo techniques were used overall. Procedure A consisted of parasagittal T1-weighted images (500/30) and axial T2-weighted images (2500/30, 2500/120). Procedure B consisted of parasagittal T2-weighted images (1600/35, 1600/90). In the parasagittal T2-weighted images clear visualization of MS lesions is achieved because signal intensities of CSF and normal nervous tissue are nearly identical. All images were performed with a 0.5 Tesla MR system. Data were obtained in 98 patients with definite (N = 30) or probable MS (N = 68). Areas with abnormal signal intensity in the infratentorial regions (brainstem, cerebellum, and/or cervical spinal cord) were identified in 44% of the patients with procedure A and in 64% with procedure B. The standard application of the combination of both procedures improves the sensitivity of the MR examination for the diagnosis of MS, the delineation of infratentorial lesions and the correlation between clinical and MR data without excessively increasing imaging time.     

Optimized pulse sequences for magnetic resonance measurement of aortic cross sectional areas

This study was done to improve the ability of magnetic resonance (MR) imaging to provide clear cross-sectional images of the ascending and descending aorta in diastole. The study was motivated by interest in measuring the regional compliance of the ascending aorta, which requires determination of the change in cross sectional area of the vessel between systole and diastole. In diastolic images, residual signal from slow flowing blood and flow artifact consistently obscured the inner boundary of the aortic wall and precluded tracing and measurement of the cross sectional area. We concluded that cross sectional area measurement of the ascending aorta was impossible on our system using standard spin echo sequences. To improve wall delineation in diastolic images, SAT pulses were optimized with respect to pulse timing, slice thickness, and gap. Optimized SAT pulses greatly improved the delineation of the vessel wall by removing unwanted signal from flowing spins. Measurement precision was vastly improved by running two scans with and without flow compensation, and correlating visually and numerically the area measurements from each. We established that each image should be measured by two independent observers and traced three times by each. Using these procedures, diastolic cross-sectional areas of the mid-ascending aorta could be measured with a precision of 2.5%, and the change of cross-sectional area between systole and diastole could be measured with a precision of 10.8%. These measurements were precise enough to detect CAD patients with low aortic compliance from the age-matched controls previously reported in one study. The test based on cross sectional area measurement, with a false positive detection rate of 5%, had a false negative rate of 58%. Compliance measurements by MR at 1.5 T could become clinically useful if normal and abnormal populations are sufficiently separated.