David D. Stark

The effects of iron oxides on proton relaxivity

The magnetic properties and relaxivities of superparamagnetic, ferromagnetic and paramagnetic iron oxides are presented and compared. The iron in colloids of ferromagnetic iron oxide has a large spin-spin relaxivity and a small spin-lattice relaxivity. The iron in colloids of paramagnetic iron oxide has a low spin-spin and spin-lattice relaxivity. The iron in colloids of highly dispersed superparamagnetic iron oxides has a large spin-spin relaxivity and a large spin-lattice relaxivity. Superparamagnetic colloids with various particle sizes in solution have been made by varying the number of superparamagnetic iron oxide crystals per particles in solution. Superparamagnetic colloids of larger solution particle size have a lower spin-lattice relaxivity than colloids comprised of smaller solution particle sizes.

Imaging by nuclear magnetic resonance in patients with chronic ischemic heart disease.

Cardiac anatomy was defined by gated nuclear magnetic resonance (NMR) imaging at a magnetic field strength of 3.5 kGauss in eight normal subjects and 10 patients with chronic myocardial infarctions. Multisectional imaging was performed with the spin-echo technique and encompassed most of the left ventricle in an imaging time of 5 to 12 min. In all subjects internal cardiac structure was well delineated without the use of any type of contrast medium. The myocardial wall-blood interface was sharply defined, resulting in visualization of trabeculations, papillary muscle, and chordal structures in both ventricles. In patients with ischemic heart disease, the extent of postinfarctional wall thinning, aneurysms, and mural thrombi were depicted on NMR images. Images obtained with the second spin-echo (delay time = 56 msec) demonstrated high signal intensity in regions of the left ventricular chamber adjacent to the site of aneurysms or infarctions; this finding suggested stasis of blood in a region of akinesis or dyskinesis. The results of this study show that gated NMR is feasible as a technique for imaging the human heart and is capable of demonstrating a variety of left ventricular abnormalities associated with chronic myocardial infarction. NMR is a completely noninvasive technique for clinical imaging of the cardiovascular system.

Resection of gastrinomas

Exploratory laparotomy and a search for gastrinomas was performed in 52 patients with the Zollinger-Ellison syndrome (ZES). Gastrinoma tissue was resected in 11 patients (21%), 6 (12%) of whom appear to have been cured. After surgery, serum gastrin levels in these six patients have remained normal from 10 months to 10 years. In the 46 other patients, tumor was unresectable because of metastases or multiple primary tumors (21 patients; 40%) or inability to find the tumor at laparotomy (21 patients; 40%). Multiple pancreatic islet cell adenomata were found in six of seven patients with multiple endocrine neoplasia (MEN), indicating that patients with this condition usually have diffuse involvement of the pancreas. The results of CT scans correlated with findings at laparotomy in 13 of 16 patients. The smallest tumor detected by CT scans was 1 cm in diameter. CT technology is more accurate in finding gastrinomas now than in the past and has a useful role in pre-operative evaluation. The possibility of resection should be seriously considered in every patient with Zollinger-Ellison syndrome. Abdominal CT scans, transhepatic portal venous sampling, and laparotomy should be used to find the tumor and to determine whether it is resectable. Using presently available methods, it should be possible to cure about 25% of patients with gastrinomas who do not have MEN and over 70% of those without MEN who appear to have a solitary tumor. Total pancreatectomy may be necessary to cure some patients with MEN, but that operation is rarely justified. The morbidity and mortality of surgical attempts at curing this disease have become minimal; we have had no deaths or serious complications following such operations in over 10 yrs. Total gastrectomy and indefinite use of H2-receptor blocking agents are the therapeutic options for patients with unresectable gastrinomas. Because H2-receptor blocking agents fail to control acid secretion in many patients after several yrs of therapy, total gastrectomy is indicated in a large proportion of patients whose tumors cannot be resected. Total gastrectomy in patients with ZES is also safe using current techniques; our last death following this operation for ZES occurred 15 yrs ago.

Magnetic resonance imaging in hypertrophic cardiomyopathy

Gated magnetic resonance imaging (MRI) was performed using a 0.35-Tesla cryogenic system in 14 patients with hypertrophic cardiomyopathy (HC) in order to define the site and extent of abnormal wall thickness. These studies were compared with 2-dimensional (2-D) echocardiograms. Gated magnetic resonance imaging studies in 12 normal volunteers were used for comparison. In normal subjects and in patients with HC, the sharp demarcation of the myocardial wall permitted measurement of wall thickness. The thickness of the septal and posterolateral walls in normal subjects was 10.2 +/- 0.4 mm (+/- standard deviation) and 10.8 +/- 0.5 mm, respectively, whereas septal thickness in all but 1 patient with HC was 15.0 mm or greater. In patients with HC, septal and posterolateral wall thickness were 2.2 +/- 0.8 cm and 1.3 +/- 0.17 cm, respectively, by MRI. The 2-D echocardiographic measurements for septal and posterolateral walls were 2.4 +/- 0.6 cm and 1.4 +/- 0.7 cm, respectively. The severity and distribution of abnormal wall thickness were comparable on 2-D echo and MRI. Gated MRI is an effective and completely noninvasive technique for demonstrating the presence, site and extent of abnormal wall thickness in HC. The large field of view, ability to image directly in multiple planes, and discrete blood-endocardial interfaces are advantages for cardiovascular imaging.

Maximizing signal-to-noise and contrast-to-noise ratios in flash imaging

This paper presents an analysis of signal-to-noise and contrast-to-noise ratios from small tip angle, gradient reversal (FLASH) imaging. Analytic and numerical techniques are used to determine the delay times and tip angles that maximize signal-to-noise per unit time from a single tissue. Similar procedures are used to determine the delay times and tip angles that maximize both T1-induced and T-2*-induced contrast-to-noise per unit time for a pair of tissues as a function of tissue characteristics and pulse sequence sampling times. The advantage of optimized FLASH imaging over optimized spin-echo imaging is quantitated by comparing signal-to-noise and contrast-to-noise ratios per unit time from the two sequences. Images are used to confirm these numerical results, to compare noise levels resulting from gradient reversals versus 180 degrees rephasing pulses and to assess the possible adverse effects of static magnetic field inhomogeneities on FLASH imaging.

Mr Imaging of Hepatic Focal Nodular Hyperplasia

The magnetic resonance features of a case of focal nodular hyperplasia are described. They include mass effect with tumor nearly isointense with adjacent liver and a central stellate region corresponding pathologically to the collagenous scar.

MRI of hepatic lymphoma

Thirteen patients with biopsy proven hepatic lymphoma (2 Hodgkin, 11 Non-Hodgkin) and a control group of 15 patients with hepatic metastases were analyzed quantitatively and qualitatively by MRI. Focal hepatic lymphoma was most reliably detected (eight of eight patients) and appeared hypointense relative to liver on T1 weighted (CNR - 7.4 +/- 2.3) and hyperintense on T2 weighted (CNR + 8.4 +/- 2.9) images. The mean T1 and T2 relaxation times of focal hepatic lymphoma (T1 = 832 +/- 234 msec, T2 = 84 +/- 16 ms) differed significantly from adjacent non-tumorous liver (T1 = 420 +/- 121 ms, T2 = 51 +/- 9 ms; p less than 0.05), however CNR values and relaxation times were similar to those of hepatic metastases. Diffuse hepatic lymphoma (microscopic periportal infiltration) was undetectable by MRI in three patients by either morphologic features or quantitative criteria. A mixed pattern of hepatic lymphoma (focal lesions and diffuse infiltration) showed focal areas of slightly decreased signal intensity on T1 weighted images (CNR = -1.7 +/- 0.4) while T2 weighted images revealed multiple regions of focal hyperintensity (CNR = +13.3 +/- 8.4) superimposed on a diffusely hyperintense liver. Our experience demonstrates that either T1 or T2 weighted techniques are useful in detecting focal and that T2 weighted techniques are useful in detecting mixed hepatic lymphoma. Conventional image derived relaxation time measurements and quantitative parameters were of no additional diagnostic value.

Computed tomography of malignant carcinoid disease

Twenty-two patients with malignant carcinoid syndrome were evaluated with CT, the largest series to date. A mass representing the primary tumor or local adenopathy was identified in four patients, appearing as a homogeneous mass involving mesentery and bowel. In two other patients the primary was not identifiable by barium series, angiography, CT, or laparotomy. In the remaining 16 patients who were scanned after resection of the primary four had mesenteric thickening and five had adenopathy. Malignant ascites was present in seven of 21 patients. All hepatic metastases were hypodense on the precontrast study. The effect of contrast administration on lesion detectability was variable, obscuring at least one or more metastases in eight of 21 scans. We recommend noncontrast scans of the liver in patients in whom the number and size of metastases are critical to therapy.

Nuclear magnetic resonance of the liver, spleen, and pancreas

This review includes the initial experience with NMR imaging of the liver, spleen, and pancreas at the University of California, San Francisco, using a prototype 0.35 Tesla system. This experience shows great promise for detection of hepatic metastases using T1-weighted pulse sequences. T2-weighted pulse sequences appear sensitive for detecting cavernous hemangioma of the liver and may allow tissue specific discrimination of the benign lesion from cancer. NMR is also suitable for evaluating diffuse metabolic alterations and is sensitive and specific for the diagnosis of iron overload. Detection of fatty liver requires use of chemical shift techniques as conventional NMR imaging pulse sequences are relatively insensitive. Motion artifacts and lack of an effective bowel contrast agent limits imaging of the pancreas and retroperitoneum, where CT remains the procedure of choice. The normal spleen has longer T1 and T2 relaxation times than liver or pancreas and NMR has not been successful in diagnosing splenic metastases or lymphoma on a routine basis. We conclude that NMR imaging will be valuable in the diagnosis of focal liver disorders; until fast scan techniques and effective magnetic contrast agents are available for oral and/or intravenous use, other abdominal applications will remain limited.

Clinical use of a nonferromagnetic needle for magnetic resonance-guided biopsy

Five patients who had liver lesions detected by magnetic resonance (MR) and/or computed tomography (CT) were biopsied using MR guidance with a specially designed nonferromagnetic needle. The 20-gauge needle was constructed from Type 316 stainless steel in order to maximize needle visibility and minimize needle-tip artifact. In all cases adequate tissue was obtained for diagnosis and no side effects were observed during the biopsy or on clinical follow-up despite the fact that the needle was within the patient in MR for an average of 30 min.