Biomedical subjects

A M Aisen

Publications and source records attributed to A M Aisen.

At least 19 recordsLinked to original sources

PubMed2004

Assessment of hepatic iron content using magnetic resonance imaging.

Numerous studies over the past decade have shown that magnetic resonance imaging (MRI) has great potential for detecting and quantifying the distribution of iron in the body. With MRI, tissue iron is indirectly identified by the paramagnetic effects of iron on the shortening of water proton MR relaxation times. However, these effects are complex and involve a number of factors, such as tissue hydration, distribution of iron and water within the tissue, and the amount of iron loading within the iron storage molecules. A coherent understanding of how these factors influence the MRI signal is still lacking. The dependence on experimental conditions, such as magnet field strength, pulse sequences, and data acquisition parameters, further complicates iron quantification with MRI. To date, there is no generally accepted MRI approach available for clinical application. In this review, we first explain the basic MR relaxation mechanisms underlying the detection of iron with MRI. We then review the literature on empirical MRI studies of hepatic iron. Finally, we summarize the critical issues that need to be addressed to develop MRI techniques for non-invasive iron detection in the body.

Humans↗

PubMed1999

A multisite phase III study of the safety and efficacy of a new manganese chloride-based gastrointestinal contrast agent for MRI of the abdomen and pelvis.

The purpose of this study was to evaluate the safety and efficacy of a manganese chloride-based oral magnetic resonance (MR) contrast agent during a Phase III multisite clinical trial. Two hundred seventeen patients were enrolled who were already scheduled for MRI of the abdomen and/or pelvis. In this group of patients, it was postulated that the use of an oral agent would better allow discrimination of pathology from bowel. Patients with known gastrointestinal pathology including peptic ulcer disease, inflammatory bowel disease, obstruction, or perforation were excluded to minimize confounding variables that could affect the safety assessment. Of these 217 patients, 18 received up to 900 mL of placebo, and 199 patients were given up to 900 mL of a manganese chloride-based oral contrast agent, LumenHance (Bracco Diagnostics, Inc.). Safety was determined by comparing pre- and post-dose physical examinations, vital signs, and laboratory examinations and by documenting adverse events. Efficacy was assessed by unblinded site investigators and two blinded reviewers who compared pre- and post-dose T1- and T2-weighted MRI scans of the abdomen and/or pelvis. In 111 (57%) of the 195 cases evaluated for efficacy by site investigators (unblinded readers), MRI after LumenHance provided additional diagnostic information. Increased information was found by two blinded readers in 52% and 51% of patients, respectively. In 44/195 cases (23%) unblinded readers felt the additional information would have changed patient diagnosis and in 50 patients (26%), it would have changed management and/or therapy. Potential changes in patient diagnosis or management/therapy were seen by the two blinded readers in 8-20% of patients. No clinically significant post-dose laboratory changes were seen. Forty-eight patients (24%) receiving LumenHance and four patients (22%) receiving placebo experienced one or more adverse events. Gastrointestinal tract side effects were most common, seen in 29 (15%) of LumenHance patients and in 3 (17%) of the placebo patients. LumenHance is a safe and efficacious oral gastrointestinal contrast agent for MRI of the abdomen and pelvis.

Abdomen↗

PubMed1999

Automated bolus chase peripheral MR angiography: initial practical experiences and future directions of this work-in-progress.

Bolus chase 3-dimensional MR angiography (3D MRA) is a recent development that extends the effective field of view for arterial imaging from the typical single 40-50 cm to over 100 cm. This technique is well suited for imaging long vascular territories such as the lower extremity. Bolus chase peripheral 3D MRA is achieved with overlapping 3D gradient-echo scans during the arterial transit of a single intravenous injection of gadolinium-chelate contrast media. This technique can depict the arteries from the infrarenal aorta to the ankles in less than 2 minutes. The initial experiences with bolus chase peripheral MRA using an automated algorithm that controls both table translation and 3D data acquisition are described. Suggestions for future refinements to the technique are also discussed.

Algorithms↗

PubMed1999

Thermoacoustic CT with radio waves: a medical imaging paradigm.

The authors evaluated images obtained with a prototypic thermoacoustic computed tomographic (CT) scanner constructed for use at 434 MHz, a promising radio frequency for detecting breast cancer. In one excised porcine kidney, acoustic energy emanating from the kidney was detected with transducers. The resultant electric signals were used to create a three-dimensional data set. Two-dimensional images reconstructed in multiple planes were compared with state-of-the-art T1- and T2-weighted magnetic resonance images. The renal outline, parenchyma, and collecting system were clearly delineated on the thermoacoustic CT images.

Acoustics↗

PubMed1996

The effect of magnetization transfer in meniscal fibrocartilage.

Magnetic resonance imaging of the knee was performed in 28 patients (ages 15-72 years), using a 1.5-T unit. Volume gradient echo (3D GRASS) acquisition with and without presaturation off-resonance RF pulse was used to evaluate magnetization transfer (MT) effects, determined by placing regions of interest on muscle, fat, hyaline, and fibrocartilage; the percent change in signal intensity was calculated and compared using a paired two-sample t test. An in vitro study of the normal meniscus from a cadaver containing a scalpel cut extending to an articular surface was performed to observe the relative improvement in contrast in the presence of a small meniscal defect. MR imaging of the specimen was performed using an Omega CSI 2.0-T system (General Electric Medical Systems, Fremont, CA). Analysis of clinical images resulted in signal loss, compared to that of the identically timed and tuned non-MT images of 47 +/- 5, 8 +/- 5, 49 +/- 5, and 57 +/- 7% for muscle, fat, articular cartilage and fibrocartilage, respectively. Application of MT improved the depiction of the artificially introduced meniscal defect. Meniscal fibrocartilage demonstrates significant MT effect after application of off-resonance RF presaturation, which may improve visualization of meniscal defects.

Adolescent↗

PubMed1996

Three-dimensional gadolinium-enhanced MR angiography for aortoiliac inflow assessment plus renal artery screening in a single breath hold.

PURPOSE: To develop a magnetic resonance (MR) angiography protocol, with use of breath-hold techniques, for simultaneous aortoiliac inflow assessment and renal artery screening in patients with lower extremity ischemia or aortic aneurysm. MATERIALS AND METHODS: Breath-hold three dimensional gadolinium-enhanced MR angiography was performed in 50 patients (conventional arteriography in 47 was the standard of reference). After multiple strategies were tested in the first 18 patients, a final protocol was formulated and tested in the subsequent 32 patients. RESULTS: The final protocol comprised a single-slab (28 3-mm-thick partitions) coronal acquisition (repetition time, 7 msec; echo time, 2.8 msec; flip angle, 60 degrees) during a single breath hold, enhanced with 30 mL gadoteridol. In the final 32 patients, sensitivity and specificity, respectively, for obstructive lesions were 100% and 100% for the aorta, 100% and 98% for common iliac arteries, 100% and 89% for external iliac arteries, 100% and 89% for main renal arteries, and 100% and 62% for accessory renal arteries. CONCLUSION: This breath-hold protocol improves the accuracy of aortoiliac inflow assessment, but low resolution limits evaluation of small renal arteries.

Adult↗

PubMed1996

CT and MR imaging in the staging of colorectal carcinoma: report of the Radiology Diagnostic Oncology Group II.

PURPOSE: To prospectively evaluate the relative accuracy of computed tomography (CT) and magnetic resonance (MR) imaging in the staging of colorectal carcinoma. MATERIALS AND METHODS: CT and MR studies were independently interpreted in a group of 478 patients with colorectal carcinoma in a study conducted from 1989 to 1993. The accuracy of each modality was assessed in a subset of 365 patients with primary tumors with respect to staging of local extent of tumor, status of local-regional lymph nodes, and the presence of liver metastases. RESULTS: In the staging of local extent of tumor, CT is more accurate than MR imaging, particularly in the definition of penetration of the muscularis propria by rectal cancer (74% vs 58%). Accuracies of CT and MR imaging were equivalent in depiction of transmural extent in colon cancers. CT and MR imaging exhibited accuracies of 62% and 64% in assessment of lymph node involvement with sensitivities of 48% and 22%, respectively. The accuracy of MR imaging and of CT (85% for each) are better for evaluation of liver metastases; lower sensitivities (62% and 70%, respectively) than specificities (97% and 94%, respectively) were demonstrated for both modalities. CONCLUSION: CT was more accurate than MR imaging in detection and characterization of transmural penetration of rectal tumors. Recent technologic advances in MR imaging may affect these results.

Aged↗

PubMed1995

Detection of degradation of magnetic resonance (MR) images: comparison of an automated MR image-quality analysis system with trained human observers.

RATIONALE AND OBJECTIVES: The perceived need for magnetic resonance (MR) imaging quality control (QC) is occasionally minimized on the assumption that significant errors will be detected by the users. To evaluate the validity of this assumption, we compared the sensitivity of a test object and automated image analysis system for MR imaging QC with the sensitivity of trained human observers by evaluating images that were intentionally degraded. METHODS: Parameters for imaging the test object and normal human volunteers were set to values that decreased the signal-to-noise ratio (SNR), caused distortion, and increased the slice thickness and separation. RESULTS: The human observers were able to detect a 6-13% reduction in the SNR and distortions of more than 15% in human images. They were unable to identify 40% increases in the slice thickness. Automated analysis of test object images was able to detect all image degradations at the minimum levels applied. CONCLUSION: The poor sensitivity of the human observers indicated that degradation, especially spatial measurements, could be significantly in error before being detected through visual analysis of clinical images. These errors would be detected by automated analysis of the test object used. Further investigation is needed to better define the accuracy with which quantitative image-quality analysis predicts the effects of degraded image quality on the ability of human observers to detect subtle abnormalities in clinical images.

Contrast Sensitivity↗

PubMed1995

Improved ejection fraction and flow velocity estimates with use of view sharing and uniform repetition time excitation with fast cardiac techniques.

PURPOSE: To improve the accuracy of ventricular volume estimates and effective temporal resolution in fast cardiac acquisitions. MATERIALS AND METHODS: Data sets at intermediate temporal phases were generated by means of sharing of views from two temporally adjacent data sets. A simulated model was used, and studies with patients and volunteers were conducted. View sharing was implemented in both fast gradient-echo and fast phase-contrast cine acquisitions; breath holding was used when possible. RESULTS: Uniform repetition time (TR) radio-frequency (RF) excitation allowed a better assessment of the end-diastolic ventricular volume. In addition, view sharing provided a better estimate of end-systolic ventricular volume in cases in which rapid changes in volume occurred at or about the temporal boundary of the source images. View sharing also provided a much smoother representation of dynamic cardiac motion when viewed in a cine loop. CONCLUSION: View sharing and uniform TR RF excitation improve the accuracy of end-systolic and end-diastolic ventricular volume measurements by improving the effective temporal resolution.

Adult↗

PubMed1995

Dynamic three-dimensional imaging with partial k-space sampling: initial application for gadolinium-enhanced rate characterization of breast lesions.

PURPOSE: To evaluate a method to monitor gadolinium enhancement patterns at magnetic resonance (MR) imaging with high temporal resolution and full coverage through both breasts. MATERIALS AND METHODS: In 12 patients with 13 masses, including nine carcinoma, nonenhanced three-dimensional MR imaging was performed with full-matrix resolution. At dynamic imaging, 32 serial passes were made during bolus administration of contrast material, and temporal resolution was reduced to 12 seconds by collecting the central (low spatial frequency) 32 x 16 or 16 x 16 phase-encode views. Full-matrix dynamic images were reconstructed by complementing central phase-encode data with precontrast data from peripheral high-spatial-frequency views. RESULTS: Results at time-course analysis with a mono-exponential saturation model indicated malignant lesions tend to show rapid (< 60 seconds) contrast change relative to benign masses and normal tissues. One cancer displayed an exceptionally slow contrast change (260 seconds). CONCLUSION: The technical objectives of full tissue coverage, rapid temporal sampling, and quantification of enhancement curves are met with this method for certain lesions (> 5 mm in largest diameter).

Adult↗

PubMed1995

Iliac artery MR angiography: comparison of three-dimensional gadolinium-enhanced and two-dimensional time-of-flight techniques.

PURPOSE: To determine if a three-dimensional (3D) gadolinium-enhanced technique is useful for improving the accuracy of magnetic resonance (MR) angiography. MATERIALS AND METHODS: Prospectively, two-dimensional (2D) time-of-flight (TOF) and 3D gadolinium-enhanced MR angiography was performed in 23 patients. Conventional arteriography, the reference standard, was performed in all but five patients. Images from each examination were interpreted blindly by two observers. RESULTS: For common and external iliac arteries, interpretations of dynamic 3D gadolinium-enhanced MR angiograms matched those of conventional arteriograms in 12 of 18 patients (67%) for both observers. Interpretations of 2D TOF images matched those of conventional arteriograms in six (33%) and seven (39%) patients for the two observers respectively. CONCLUSION: Preliminary results suggest that iliac artery MR angiography can be improved by complementing standard 2D TOF acquisitions with 3D gadolinium-enhanced acquisitions.

Angiography↗

PubMed1995

Characterization of adrenal masses with chemical shift and gadolinium-enhanced MR imaging.

PURPOSE: To assess the potential role of chemical shift and dynamic gadolinium-enhanced magnetic resonance (MR) imaging in the characterization of adrenal masses. MATERIALS AND METHODS: Fifty-one adrenal masses (35 adenomas and 16 nonadenomas) in 43 patients were evaluated with chemical shift MR imaging, dynamic gadolinium-enhanced MR imaging, or both. The relative change in the signal intensity (SI) ratio of the adrenal mass to liver and paraspinal muscles was quantitatively and qualitatively assessed. Opposed-phase gradient-echo (GRE) images were compared with in-phase images. RESULTS: With qualitative visual inspection, only adenomas showed a decrease in relative SI ratio on opposed-phase chemical shift images (specificity, 100%; sensitivity, 81%). Quantitative ratios corresponding to 100% specificity were also observed, with similar sensitivities. Adenomas could not be differentiated from nonadenomas with visual assessment of maximum SI after contrast material administration or washout. CONCLUSION: Characterization of an adrenal mass as an adenoma can be made with high specificity and acceptable sensitivity by visually comparing opposed-phase with in-phase GRE images.

Adenoma↗

PubMed1994

Detection of liver fibrosis with magnetic cross-relaxation.

The utility of MRI using magnetization transfer (MT) enhanced pulse sequences to diagnose hepatic cirrhosis in a rat model was investigated. Hepatic T1 was measured with and without MT off-resonance RF pulses in 17 treated and six control rats. The livers were evaluated histologically, and the hydroxyproline content quantitatively measured. We did not find a statistically significant linear correlation between the MR relaxation times and the degree of tissue injury. However, the MR measurements performed with MT were superior to those without differentiating the treated and control groups. Specifically, the T1 times were 695 +/- 76 ms for the treated group, versus 748 +/- 61 ms in the controls; P = 0.095. The T1sat times were also lower in the treated group, with statistical significance: 367 +/- 51 ms versus 421 +/- 38 ms, P = 0.016. Finally, the change in the relaxation rates (the inverse of the relaxation times) with and without saturation were 1.31 +/- 0.22 s-1 (treated group) versus 1.05 +/- 0.12 s-1 (controls), which differed significantly, P = 0.001.

Animals↗

PubMed1994

Magnetization transfer contrast imaging of hepatic neoplasms.

A method of performing magnetization transfer contrast (MTC) using a pulse sequence based on a series of on-resonance binomial pulses preceding a conventional spin-echo sequence has been recently described. We investigated this technique in the evaluation of circumscribed hepatic neoplasms on a 0.5 T imager. Conventional spin-echo imaging was performed in 18 patients with hepatic neoplasms, 15 with primary or metastatic hepatic neoplasms, and 3 with cavernous hemangiomas. The T1-weighted sequence was repeated following MTC saturation in 7 patients and the proton density sequence was repeated following MTC saturation in 13 patients (both were used in two patients). The mean lesion-to-liver contrast for neoplasms worsened with T1-MTC (0.87 vs. 1.04), but improved slightly with proton density-MTC (1.10 vs. 1.22) when compared to the corresponding non-MTC spin-echo images. However, these differences were not statistically significant (p = .19 and p = .16, respectively). The limited data on cavernous hemangiomas does not suggest these have consistently different MTC imaging characteristics from other hepatic neoplasms. In conclusion, MTC imaging using a binomial saturation pulse did not offer significant improvement in contrast between hepatic neoplasms and normal liver. Refinements of the binomial pulse sequence will be necessary if a consistent improvement in lesion sensitivity is to be achieved. Evaluation of its role in increasing diagnostic specificity will require further investigation.

Adenoma↗

PubMed1994

Evaluation of quantitative magnetic resonance imaging as a noninvasive technique for measuring renal scarring in a rabbit model of antiglomerular basement membrane disease.

Renal function tests are an insensitive means of detecting progressive scarring of the kidney such as occurs in chronic allograft rejection and lupus nephritis. Alternative approaches for the measurement of small progressive changes in renal structure on a repetitive basis are needed. Quantitative magnetic resonance imaging (proton T1 relaxation time) was assessed for this purpose. A rabbit model of antiglomerular basement membrane disease that develops glomerular and interstitial inflammation followed by scarring of the renal cortex was used. Longitudinal studies of cortical T1 showed a marked prolongation of T1 during the initial inflammation and edema associated with glomerular crescent formation (Day 7). The T1 remained prolonged up to Day 120 in animals with significant fibrosis and crescent formation when the wet/dry weight ratio (a measure of edema) had returned to baseline. T1 was a more sensitive index of renal injury than was serum creatinine for all of the end points measured (cortical hydroxyproline per dry weight, percent crescent formation, or histologic fibrosis score). It was concluded from these studies that measurement of renal cortical T1 is quite a sensitive index of renal injury, probably more sensitive than the measurement of serum creatinine, but that this method does not discriminate between edema and scarring.

Animals↗

PubMed1993

Use of the magnetic resonance contrast agent gadodiamide in the central nervous system. Results of a multicenter trial.

To investigate the safety and efficacy of the low-osmolar, nonionic contrast agent, gadodiamide injection (Omniscan, Sanofi Winthrop Pharmaceuticals, New York, NY), for magnetic resonance imaging (MRI) of the head and spine, a multicenter study involving 439 patients was done at 15 centers as part of a Phase II/III clinical trial. Unenhanced MRI scans were obtained after which the patients were injected with 0.1 mmol/kg gadodiamide, and the MRI was repeated. The patients' vital signs were monitored, and laboratory studies were conducted. Neurologic status was examined before and after the study. The images were evaluated for contrast enhancement. No patient had any significant adverse event or serious change in clinical status. Abnormalities were found in 80% (351) of all patients studied, and it was found that, in 75% (266) of these, the postgadodiamide injection images were improved or facilitated visualization of lesions compared with preinjection images. The investigators believe that, based on the results of this study, gadodiamide injection is safe and effective for imaging the head and spine. They suggest that future studies further assess and compare the safety parameters of gadodiamide injection with those of other nonionic and ionic gadolinium ligands.

Central Nervous System Diseases↗

PubMed1993

Thoracic cardiovascular anomalies in children: evaluation with a fast gradient-recalled-echo sequence with cardiac-triggered segmented acquisition.

A fast gradient-recalled-echo sequence with cardiac-triggered segmented acquisition (fastcard) was compared with a standard T1-weighted spin-echo sequence with cardiac gating and respiratory compensation in the evaluation of pediatric patients with thoracic cardiovascular anomalies. Twenty patients aged 1 week to 24 years (median age, 9 months) with various abnormalities underwent magnetic resonance (MR) imaging. In 18 patients, MR imaging was performed with both gated spin-echo and fastcard. Two observers rated the clinical utility of each sequence. Fastcard images were superior to spin-echo images in 10 patients, equivalent in seven, and inferior in one. Two additional patients with suspected pulmonary vascular lesions were accurately evaluated with the fastcard technique. The fastcard technique provides superior demonstration of thoracic cardiovascular structures and turbulent flow and enables imaging in multiple phases of the cardiac cycle.

Adolescent↗

PubMed1993

"Anatometabolic" tumor imaging: fusion of FDG PET with CT or MRI to localize foci of increased activity.

Positron emission tomographic (PET) images of visceral cancers are commonly visualized as "hot spots" of increased activity with relatively little normal anatomy discernable, when 2-[18F]-fluoro-2-deoxy-D-glucose (FDG) is used as the tracer. We describe a method by which computed tomography or magnetic resonance anatomic images can be digitally fused in three dimensions, using a rigid rotate-translate scale model with PET "metabolic" images, to simultaneously display registered anatomic and metabolic information. Such "anatometabolic" fusion images were produced in 10 patients with a variety of visceral cancers. External fiducial markers placed during both the anatomic and the metabolic study, as well as internal anatomic fiducials defined from landmarks observed on reconstructed transmission images, were used to achieve image fusion. The mean error magnitude +/- s.e.m. of fiducial registration in the nine patients with successful realignments was 5.0 +/- 0.8 mm. The mean accuracy in realignment between known anatomic structures seen on both the anatomic study and on the emission PET scan (but not used in realignment) was 6.3 +/- 0.8 mm. Localization of foci of increased FDG uptake to specific anatomic structures was achieved by this method, which represented an enhancement over the rudimentary anatomy available from the emission images alone. Anatometabolic fusion images made using this reasonably simple method should prove useful in the management of patients with cancer and other diseases.

Adult↗