Scott A. Mirowitz

Evaluation of pulmonary arterial morphology in cyanotic congenital heart disease by magnetic resonance imaging

Before and after surgical therapy, the anatomy of the pulmonary arteries in cyanotic congenital heart disease is often distorted. Pulmonary arterial anatomy was evaluated by magnetic resonance imaging (MRI) and angiography in 20 patients, ages 3 months to 20 years, with cyanotic heart disease associated with decreased pulmonary blood flow. Excellent correlation between MRI and angiographic estimates of pulmonary artery diameter was obtained (main pulmonary artery, r = 0.96; right pulmonary artery, r = 0.93; left pulmonary artery, r = 0.96). A similar excellent correlation (kappa = 0.83) was found in the assessment of the presence and severity of proximal pulmonary arterial stenoses. However, stenoses in the peripheral pulmonary arteries visualized with angiography were missed with MRI. MRI and angiography showed complete agreement in determining the patency of 11 surgical shunts. MRI did not demonstrate all of the systemic collateral vessels present with angiography, and the distal connections of collaterals were not detected with MRI. MRI is comparable to angiography in the evaluation of central pulmonary arterial anatomy over a wide range of ages. These findings suggest an important role for noninvasive MRI in the serial evaluation of pulmonary artery morphology in patients with cyanotic congenital heart disease before and after surgical repair.

Fast T2-weighted MR imaging: impact of variation in pulse sequence parameters on image quality and artifacts.

The purpose of this study was to quantitatively evaluate in a phantom model the practical impact of alteration of key imaging parameters on image quality and artifacts for the most commonly used fast T(2)-weighted MR sequences. These include fast spin-echo (FSE), single shot fast spin-echo (SSFSE), and spin-echo echo-planar imaging (EPI) pulse sequences. We developed a composite phantom with different T1 and T2 values, which was evaluated while stationary as well as during periodic motion. Experiments involved controlled variations in key parameters including effective TE, TR, echo spacing (ESP), receive bandwidth (BW), echo train length (ETL), and shot number (SN). Quantitative analysis consisted of signal-to-noise ratio (SNR), image nonuniformity, full-width-at-half-maximum (i.e., blurring or geometric distortion) and ghosting ratio. Among the fast T(2)-weighted sequences, EPI was most sensitive to alterations in imaging parameters. Among imaging parameters that we tested, effective TE, ETL, and shot number most prominently affected image quality and artifacts. Short T(2) objects were more sensitive to alterations in imaging parameters in terms of image quality and artifacts. Optimal clinical application of these fast T(2)-weighted imaging pulse sequences requires careful attention to selection of imaging parameters.

Cavernous hemangioma of the liver: assessment of MR tissue specificity with a simplified T2 index.

This is a comparison of the ability of two quantitative magnetic resonance (MR) indices: (a) the second echo signal drop (SESD) (a simplified index of T2 relaxation times that we have developed); and (b) the previously described lesion/liver signal intensity ratio (LLR) to provide histologic diagnosis in hepatic lesions greater than 2 cm in diameter. In 55 patients 108 hepatic masses [31 cavernous hemangiomas (CH), 68 metastases, and 9 hepatocellular carcinomas] were scanned at 0.5 T. Statistically significant differences between CH and malignant lesions were obtained in mean SESD (p = 0.0006) and LLR (p = 0.0008) using repetition time (TR) 2,100/echo time (TE) 35, 60 ms. Application of cutoff values derived from receiver-operator characteristic analysis led to a correct diagnosis in 100 and 94% of lesions, respectively. Using TR 2,100/TE 35, 90 ms in a different patient population, CH and malignancies again displayed significantly different mean values, using the SESD (p = 0.0090) and LLR (p = 0.0024) methods. These measurements provided a correct diagnosis in 74 and 81%, respectively. Accuracy was increased in those cases in which the diagnosis by SESD and LLR were concordant. When compared with visual analysis, these quantitative methods appear to achieve near 100% accuracy in the differentiation of hepatic CH from malignancies.

Manifestation of magic angle phenomenon: comparative study on effects of varying echo time and tendon orientation among various MR sequences

The purpose of this study was to systematically investigate the effect of varying the echo time (TE) values and angle of the tendon to the main magnetic field (B(o)) upon the signal intensity observed with the magic angle phenomenon in tendons among most commonly used MR pulse sequences, including conventional spin echo (CSE), fast spin echo (FSE) and gradient echo (GRE) sequences. The intact bovine Achilles tendon was imaged using a clinical 1.5-T MR scanner. Magic angle phenomenon occurs in CSE, FSE and GRE sequences with different grade, appearing most severe in CSE, middle in FSE, and weakest in GRE sequence. In addition, the tendon signal changes produced by the magic angle phenomenon could be greatly reduced by increasing the TE to above a certain critical value in all three sequences. These critical TE values were different among CSE (40 msec), FSE (70 msec), and GRE (30 msec) sequences.

Neurodegenerative diseases of childhood: MR and CT evaluation.

To evaluate the diagnostic utility of MR and CT in neurodegenerative diseases of childhood, we examined 63 children (MR in 44, CT in 53) carrying diagnoses of Leigh disease (14 patients), various metabolic diseases (13 patients), leukodystrophies (13 patients), other specific degenerative diseases (10 patients), and unclassified neurodegenerative disorders (13 children). Magnetic resonance yielded positive findings in 86% and CT in 81%. Lesion extent and conspicuity were consistently greater with MR. The high frequency of abnormalities detected on MR, and to a lesser extent on CT, helps distinguish children with neurodegenerative diseases from those with nonprogressive idiopathic movement disorders. The most common abnormalities included signal alterations (MR) or decreased attenuation (CT) of the basal ganglia and cerebral white matter, as well as local or generalized brain atrophy. Although considerable overlap was present, the findings showed four general patterns that may assist in tentative classification of patients with nonspecific clinical and laboratory findings.

Performing cardiac MR imaging: an overview

Because of the enormous economic and social impact of cardiovascular disease in the United States, there is a need for improved noninvasive diagnosis. Cardiac MR imaging is a versatile, comprehensive technique for assessing cardiac morphology and function. With an understanding of cardiac anatomy and physiology as well as MR physical principles, cardiac MR imaging can be performed and play an important role in patient management.

Use of nutritional support formula as a gastrointestinal contrast agent for MRI

The objective of this study was to evaluate the potential utility of a nutritional support formula to serve as a practical means of enhancing the gastrointestinal tract on abdominal MR images. Nutritional support formula (Ensure Plus) was administered to 29 patients prior to abdominal MRI. Standard T1-weighted and T2-weighted pulse sequences were performed, in addition to fat suppression and inversion recovery sequences in selected patients. Images in these patients were evaluated for degree and uniformity of gastrointestinal tract enhancement and delineation of the bowel wall and pancreas. Results were compared with those obtained in 10 control patients. Marked enhancement of gastric contents was present in nearly all patients who received nutritional support formula on both T1-weighted and T2-weighted sequences, with mild to moderate enhancement of small bowel and colon in most patients. Although gastrointestinal and respiratory motion artifacts often limited bowel wall delineation, excellent delineation of the gastric wall and pancreas was provided. Phantom experiments demonstrated that gastrointestinal tract enhancement with nutritional support formula is due to the paramagnetic trace elements, corn syrup, and lipid material it contains. Such a formula requires no preparation, is safe, inexpensive, palatable, readily available, and represents a practical means of enhancing the gastrointestinal tract on MRI.

Comparative study of fast MR imaging: quantitative analysis on image quality and efficiency among various time frames and contrast behaviors.

The purpose of this study is to quantitatively compare the image quality and efficiency provided by widely available fast MR imaging pulse sequences. A composite phantom with various T1 and T2 values and subjected to periodic motion was imaged at 1.5 T. The fast MRI sequences evaluated included fast spin-echo (FSE), single shot fast spin-echo (SSFSE), echo-planar imaging (EPI), multi-slice gradient recalled (MPGR), fast MPGR (FMPGR), and fast multi-slice spoiled gradient echo (FMPSPGR). T1-weighted (T1WI), T2-weighted (T2WI), proton-density-weighted (PDWI), and T2*-weighted (T2*WI) images were evaluated in breath-hold and non-breath-hold time frames. Analysis included measurement of image signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), nonuniformity, ghosting ratio, SNR per unit time and CNR per unit time. Among fast T2WI sequences, FSE with breath-hold time frame resulted in the highest image quality and in superior SNR and CNR efficiency by a factor of 5 or 6 as compared with conventional spin echo sequence. Among fast T1WI sequences, FMPGR and FMPSPGR both with non-breath-hold time frame produced the highest image quality and SNR and CNR efficiency by a factor of greater than 5 as compared with conventional spin echo. Among fast PDWI and T2*WI sequences, FSE produced the highest SNR and CNR, and was maximally efficient with a factors of greater than 6 as compared with conventional spin echo.

CT depiction of prostatic zonal anatomy.

The objective of this study was to investigate the frequency of recognition of prostatic zonal anatomy on CT. Computed tomography in 71 patients without known prostate disease was reviewed. Differential attenuation allowed for distinction of the peripheral zone and central gland of the prostate in 24% patients. The peripheral zone was of lower attenuation than the central gland, attributable to relatively increased water content in the peripheral zone. Patients in whom zonal anatomy was evident were significantly older and had prostate glands significantly larger than those in whom the prostate appeared as a homogeneous structure. All patients in whom prostatic zonal anatomy was visualized had received intravenous contrast material injection. Development of benign prostatic hyperplasia nodules within the central gland may contribute to relative increased attenuation or increased contrast enhancement within this region of the prostate gland.

Contrast Enhancement of the Gastrointestinal Tract on MR Images Using Intravenous Gadolinium-DTPA

Gadopentetate dimeglumine was administered intravenously to 16 patients undergoing abdominal magnetic resonance (MR) imaging. T1-weighted and fat-suppressed T1-weighted images were acquired before and after intravenous administration of 0.1 mmol/kg gadopentetate dimeglumine. The stomach, small bowel, and colon were analyzed regarding the presence and relative intensity of contrast enhancement. Diffuse enhancement of the gastrointestinal tract wall was observed in all patients following contrast material administration. Such enhancement was most conspicuous on fat-suppressed T1-weighted images. Quantitative measurements indicated that the wall of the gastrointestinal tract enhanced approximately 100% with gadopentetate dimeglumine. This study demonstrates that enhancement of the normal gastrointestinal tract occurs routinely when intravenous gadopentetate dimeglumine is administered, and such enhancement should not be considered indicative of gastrointestinal pathology. Furthermore, it suggests the potential utility for using intravenous rather than orally administered contrast agents to provide enhancement of the gastrointestinal tract on MR images.