Dynamic fluctuations in blood and spleen radioactivity: splenic contraction and relation to clinical radionuclide volume calculations.

Alterations in the blood radioactivity affect ventricular volume calculations using count-based radionuclide ventriculography. To study this phenomenon, the effect of time, posture and supine exercise on blood radioactivity, red blood cell count and splenic radioactivity was evaluated. The red blood cell count, and blood, splanchnic and splenic radioactivity remained stable in five patients studied at rest in the supine position. On standing, blood radioactivity increased 10 +/- 3% (standard error of the mean), and abdominal radioactivity decreased 14.5 +/- 6.5% (both p less than 0.05). In 10 patients, splenic radioactivity decreased after supine exercise by 49 +/- 7%, while blood radioactivity increased 10.5 +/- 1.5% and red blood cell count increased 7.5 +/- 1.5% (all p less than 0.001). Splenic radioactivity increased gradually after exercise and decreased after a second exercise period. In the exercising patients, blood radioactivity increased by 14.5% and correlated with an increase in the red blood cell count (r = 0.57, p = 0.01, 19 samples from 10 patients). Reduction in splenic radioactivity also correlated with the increase in red blood cell count (r = -0.51, p = 0.025). The data demonstrate splenic shrinkage in human beings and an inverse relation between changes in splenic and blood radioactivity. These dynamic fluctuations emphasize the need for simultaneous blood sampling for accurate calculation of left ventricular volume and high-light the importance of regional volume shifts during exercise.

Midsagittal sections of the cerebellar vermis and fourth ventricle obtained with magnetic resonance imaging of schizophrenic patients.

Measurements of the cerebellar vermis and height of the fourth ventricle made from midsagittal brain images obtained with magnetic resonance imaging did not show any differences between patients with schizophrenia and matched normal control subjects.

Prediction of benignancy of the solitary "cold" thyroid nodule by fluorescent scanning.

A quantitative x-ray fluorescent scanning technique has been used routinely to determine iodine content ratios (ICR) of nodule to normal thyroid tissue in patients with solitary "cold" thyroid nodules. A study of 150 patients with histological diagnoses has shown that an ICR above 0.60 is an excellent indicator of benignancy with a sensitivity of 63% and a specificity of 99%. This technique, in conjunction with careful clinical judgment, can be used to identify those patients that are at low risk for malignancy and can probably undergo conservative clinical management.

Cerebral venous angioma: correlation of radionuclide brain scan, transmission computed tomography, and angiography.

Three cases of intracerebral venous angioma, a rare vascular malformation, were studied by radionuclide brain scan, transmission computed tomography (TCT) and angiography. In each case, the radionuclide flow study demonstrated a typical area of abnormal increase in activity during the venous phase; in two of the cases the arterial phase was also abnormal. Each contrast angiogram demonstrated a normal arterial distribution and a characteristic network of abnormal veins that converged to a large transcerebral draining vein. The TCT scans showed enhancing, curvilinear densities; while not specific, this finding should suggest the possibility of venous angioma in the brain.

Potential pitfalls of magnetic resonance imaging in the diagnosis of avascular necrosis.

Magnetic resonance (MR) imaging and radionuclide (RN) bone scans were performed in two patients with collagen vascular disease (CVD) to evaluate hip pains. In both patients RN bone scans demonstrated decreased radioactivity in the femoral heads, whereas, MR imaging was normal. Because early changes of avascular necrosis (AVN) frequently present as decreased radioactivity in the femoral head, special attempts were made to detect this decreased activity using pinhole collimator imaging. The diagnosis of AVN was confirmed surgically by venous pressure measurements. Abnormal RN bone scans representing decreased flow due to vasculitis in patients with CVD, may be more sensitive in the diagnosis of AVN before structural changes can be detected on MR studies.

Congenital absence of the gallbladder: another cause of false-positive hepatobiliary image.

Hepatobiliary imaging with the various technetium-labeled IDA compounds is more than 90% sensitive and specific for the diagnosis of acute cholecystitis. Causes of false-positive studies include chronic cholecystitis, cystic-duct obstruction by tumor, prolonged fasting, the nonfasting state, pancreatitis, alcoholism, parenteral hyperalimentation, and severe intercurrent illness. A case of congenital absence of the gallbladder is submitted as another cause of a false-positive scan.

The value of the bone scan in idiopathic regional migratory osteoporosis.

Idiopathic regional migratory osteoporosis is a self-limited entity of unknown origin, which has received little attention in the nuclear medicine literature. It is characterized by severe joint pain, typically in a hip, with normal laboratory and normal early radiographic findings. Spontaneous recovery occurs, but recurrence is frequent in another joint, often the opposite hip. Recurrence in the same joint has never been reported. The bone scan is shown to be positive with first symptoms and is important in the diagnosis and management of this entity. Three cases are presented.

Clinical magnetic resonance imaging with nuclear medicine correlation.

The current role of magnetic resonance imaging (MRI) in different organ systems is discussed and compared to nuclear medicine and to other available clinical diagnostic modalities. The value of optimizing radiofrequency pulse sequence selection to provide additional tissue characterization is also described. The results of nuclear medicine and MRI studies in 56 patients are compared to evaluate the clinical diagnostic contribution of each imaging modality for various pathological processes. In addition, the state-of-the-art MRI systems and future development in MRI technology with its potential contribution is defined.

Evaluation of intrathoracic goiter with I-123 scintigraphy and nuclear magnetic resonance imaging.

Iodine-123 thyroid scintigraphy allows the diagnosis of a functioning retrosternal goiter in a patient with a mediastinal mass. The case report of a 60-yr-old lady demonstrates this. The correlative values of nuclear magnetic resonance imaging and thyroid scintigraphy in the initial evaluation and continued management of patients with thyroid mediastinal mass are presented. In addition, this observation demonstrates the ability of nuclear magnetic resonance to identify retrosternal thyroid tissue. This may obviate the need for TCT evaluation, which involves both ionizing radiation and iodinated contrast enhancement.

Radionuclide stroke count ratios for assessment of right and left ventricular volume overload in children.

The ratio of left ventricular to right ventricular stroke counts measured by radionuclide angiography has been used in adults to estimate the severity of left-sided valvular regurgitation. The validation of this technique in children for assessment of right and left ventricular volume overload is reported herein. Radionuclide stroke count ratios in 60 children aged 0.5 to 19 years (mean 11) were determined. Based on their diagnoses, the patients were divided into 3 groups: (1) normal--40 patients with no shunts or valvular regurgitation, (2) left ventricular volume overload--13 patients with mitral or aortic regurgitation, or both, and (3) right ventricular volume overload--7 patients, 2 with severe tricuspid regurgitation, 3 with atrial septal defects, and 2 with total anomalous pulmonary venous drainage. The radionuclide stroke count ratio clearly differentiated these groups (p less than 0.05): normal patients had a stroke count ratio of 1.04 +/- 0.17 (mean +/- 1 standard deviation), the left ventricular volume overload group had a stroke count ratio of 2.43 +/- 0.86, and the right ventricular volume overload group had a stroke count ratio of 0.44 +/- 0.17. In 22 of our 60 patients, radionuclide stroke count ratios were compared with cineangiographic stroke volume ratios, resulting in a correlation coefficient of 0.88. It is concluded that radionuclide ventriculography is an excellent tool for qualitative and quantitative assessment of valvular regurgitation in children.

Evaluation of left ventricular performance using digital subtraction angiography.

Cardiac applications for digital subtraction angiography appear promising, but few correlative studies with contrast ventriculography have been done. Left ventricular volume, ejection fraction, and regional wall motion by digital subtraction angiography were evaluated after intravenous injection of 40 ml of iodinated contrast medium and after left ventricular injection of 5 to 10 ml of contrast medium. A film-based system of the authors' own design was used. Results were compared with those after direct left ventricular injection of 40 ml of contrast medium. The ventriculograms after intravenous injection were of diagnostic quality in 9 of 12 studies, and there were close correlations between intravenous and direct-injection studies for left ventricular ejection fraction (r = 0.89, n = 9, and p = 0.001) and for left ventricular volume (r = 0.91, n = 18, and p less than 0.001). Regional wall motion scores showed close correspondence in 83% of sectors. After small-volume left ventricular injections, the ventricular image was enhanced considerably by digital subtraction. Correlations between small- and large-volume ventriculograms were close for left ventricular ejection fraction (r = 0.91, n = 8, and p = 0.002) and for left ventricular volume (r = 0.96, n = 16, and p less than 0.001). There was close correspondence of wall motion scores in 87% of sectors. Thus, digital subtraction angiography improves the visibility of the left ventricle after either intravenous or small-volume direct left ventricular injection. Digital images produce excellent estimates of left ventricular volume and should have considerable usefulness for the study of cardiac performance and anatomy.

Multiple imaging modalities for the study of pancreatic disease.

Gray scale ultrasonography (US) and computed tomography (CT) have enhanced the role of various imaging modalities in the evaluation of patients with suspected pancreatic disease. When these anatomical studies are normal or equivocal, a functional, radionuclide pancreas scan may be useful. Pancreatic imaging can be achieved using ultrasound, transmission CT, single photon radionuclide imaging, and positron emission CT. A diagnostic imaging decision chart for the evaluation of patients with possible pancreatic disease is useful in choosing the correct imaging modality in a specific situation. Such a chart and its theoretic basis are described in this review. The need to optimize the pancreatic work-up with respect to cost-benefit decisions and diagnostic accuracy, sensitivity, and specificity are of particular concern to the physician. Of all the potential areas for disease, the pancreas has been and remains a particularly difficult diagnostic problem.

Quantitative imaging of renal blood flow and function.

Noninvasive renal blood flow quantitation has been historically difficult, although radionuclide imaging methods for measuring related parameters of renal function such as glomerular filtration rate and effective renal plasma flow have been successful. Radionuclide methods have long played an important role in the evaluation of renal function, but recent advances in other modalities such as positron emission tomography (PET), computed tomography (CT), and magnetic resonance imaging (MRI) have the potential to provide information not available with nuclear medicine techniques. The high spatial resolution provided by these modalities, coupled with dynamic imaging of contrast agents or radioactive tracers, potentially could allow detailed clinical evaluation of regional renal function and blood flow. A specialized MR technique, diffusion-weighted imaging, also shows promise for providing information not otherwise available concerning the renal microcirculation. This report provides a brief review of the available clinical techniques for the evaluation of renal blood flow and function as well as new methods under investigation.

Magnetic resonance angiography techniques.

After a radio frequency pulse, the decay of the magnetic resonance (MR) signal is described by two relaxation processes, T1 and T2. T1 describes the rate at which the magnetization realigns itself along the external magnetic field direction (ML), and T2 describes the rate of decay of the magnetization component along the transverse axis (MT). Magnetic resonance angiography (MRA) sequences have been developed that encode flow as changes in the apparent T1 or T2 of the moving blood relative to stationary tissues. MRA sequences typically use either time-of-flight (TOF) techniques to encode T1 or phase-contrast techniques to encode T2. TOF techniques encode flow as an apparent T1 shortening through the wash-in of fully relaxed blood from outside the image volume. The shorter T1 produces an enhancement of vascular structures relative to stationary tissues. TOF methods may use either sequential two-dimensional, three-dimensional, or multi-slab three-dimensional imaging sequences to produce a three-dimensional MRA data set. Phase-contrast methods use additional magnetic field gradients to encode flow as shifts in the phase of MT. Both TOF and phase-contrast methods use maximum intensity projection (MIP) images displayed in a cine format to aid in the visualization of three-dimensional vascular structures.

Magnetic resonance imaging of ischemic bowel in rabbit model.

Acute mesenteric ischemic bowel disease is a common yet complex disorder with high morbidity and mortality rates predominantly caused by delayed diagnosis. We examined the role of magnetic resonance imaging (MRI) in the early detection of small bowel ischemia using the rabbit model. Surgical ligation of the appropriate arterial vascular supply to the ileum of 10 rabbits produced the ischemic compromise. The animals were imaged at different time intervals after the arterial occlusion. Multislice, T1 and T2-weighted images were obtained in axial and coronal planes. Abnormal findings of the dearterialized segment of bowel were visualized as early as 45 minutes after vascular occlusion. The findings consisted of: (1) bowel wall thickening, (2) two- to three-fold increase in signal intensity from bowel on T2-weighted images, and (3) isointensity or slightly increased signal intensity within the bowel wall on T1-weighted images. MRI appears to be a sensitive, noninvasive technique for the early detection of bowel ischemia in the rabbit animal model.

Enhancement of red blood cell proton relaxation with chromium labeling.

Nuclear medicine has utilized chromium (Cr) for decades to label red blood cells (RBCs). The purpose of this project was to determine whether sufficient paramagnetic Cr could be bound to red cells to influence proton relaxation significantly. We demonstrated that the T1 and T2 of RBCs can be substantially shortened by labeling them with paramagnetic Cr. Proton relaxation enhancement occurs when red cells are incubated with sodium chromate (VI) over a concentration range of 0.10 mM to 31.6 mM. Labeling with Cr at a concentration of 31.6 mM shortened the T1 of packed cells from 714 msec to 33 msec, and the T2 from 117 msec to 24 msec, as compared with nonlabeled red cells. In vitro hemolysis was significantly increased after labeling at 31.6 mM, but not at lower concentrations. Cr-induced proton relaxation enhancement varied with RBCs from different species, temperature, pH, and length of incubation. T1 values of kidneys containing labeled red cells (303 msec), or labeled cells diluted 10-fold with nonlabeled cells (479 msec), were decreased compared with kidneys containing only nonlabeled cells (600 msec). Finally, preliminary data indicate that the signal intensity of perfused renal tissue is significantly influenced in vivo by infusion of Cr-labeled RBCs. This study demonstrated that Cr labeling of RBCs sufficiently enhances red cell proton relaxation to provide excised organs containing red cells, of which 10% have been Cr-labeled, with shorter T1 and T2 values than organs containing nonlabeled cells. In addition, the ability of labeled cells to alter signal intensity in vivo suggests that Cr may have the potential to become an MRI contrast agent.

AUR memorial award--1988. MRI enhancement of perfused tissues using chromium labeled red blood cells as an intravascular contrast agent.

It has been demonstrated that chromium (Cr) labeling significantly decreases the relaxation times of packed red blood cells (RBCs). In this study, the spin-lattice relaxation time (T1) of human red cells was shortened from 836 ms to 29 ms and the spin-spin relaxation time (T2) shortened from 134 ms to 18 ms, when the cells were labeled at a Cr incubation concentration of 50 mM. Labeling of canine cells at 50 mM resulted in a T1 of 36 ms and a T2 of 26 ms. A labeling concentration of 10 mM produced similar relaxation enhancement, with uptake of 47% of the available Cr, and was determined to be optimal. The enhancement of longitudinal and transverse relaxation rates (1/T1,-1/T2) per amount of hemoglobin-bound Cr are 6.9 s-1 mM-1 and 9.8 s-1 mM-1 respectively, different from those of a pure Cr+3 solution. Labeling cells at 10 mM decreased the survival half-time in vivo from 16.6 days to 4.7 days in dogs. No difference in red cell survival was found with the use of hetero-transfusion versus auto-transfusion of labeled RBCs. Significant shortening of the T1 (912 ms to 266 ms, P = .03) and T2 (90 ms to 70 ms, P = .006) of spleen and the T1 (764 ms to 282 ms, P = .005) and the T2 (128 ms to 86 ms, P = .005) of liver occurred when 10% of the RBC mass of dogs was exchanged with Cr labeled cells. Liver and spleen spin density changes (P greater than 0.23) and muscle spin density and relaxation changes (P greater than 0.4) were insignificant. The in vivo T1 of a canine spleen which had been infarcted did not change following transfusion with labeled cells, where the T1 of liver did shorten. We believe this preliminary study suggests that Cr labeled red cells may have the potential to become an intravascular magnetic resonance imaging contrast agent.

Paramagnetic NMR contrast agents. Development and evaluation.

Paramagnetic ions could be theoretically used as NMR contrast agents because of their effect upon T1. However, the toxicity of these ions prevents their application. By the formation of appropriate chemical complexes with these ions, the toxicity of these agents can be substantially reduced while maintaining the paramagnetic effect. Two potential NMR contrast agents, one for oral use and one for intravenous administration, were developed and evaluated both in vitro and in vivo. The effect upon T1 in vitro of these paramagnetic compounds was determined using a JEOL FX-90Q NMR spectrometer. These agents were evaluated in vivo in dogs with a Technicare 0.3 tesla superconducting magnet system and in rabbits with the Aberdeen 0.04 tesla resistive NMR imager. Using calculated T1 NMR images, a nontoxic dose of gadolinium oxalate provided visualization of the gastrointestinal tract. Intravenous administration of chromium EDTA provided enhancement of the kidneys, ureters, and bladder, thereby potentially allowing for the evaluation of renal function with magnetic resonance imaging. Stable paramagnetic complexes can serve as effective, nontoxic, oral and intravenous NMR contrast agents.

Magnetic resonance imaging of the brain in isolated optic neuritis.

Magnetic resonance imaging of the brain was performed on ten patients who had isolated optic neuritis. Seven patients had abnormal images, with a distribution of lesions similar to that seen in multiple sclerosis, demonstrating subclinical dissemination in the central nervous system.

Dyke Award. Evaluation of contrast-enhanced MR imaging in a brain-abscess model.

An alpha-streptococcus brain abscess was produced in five dogs and studied with magnetic resonance (MR) imaging (0.5 T) and computed tomography (CT). Non-contrast- and contrast-enhanced CT scans were obtained using gadolinium diethylenetriamine-pentaacetic acid (Gd DTPA) for MR imaging and meglumine iothalamate for CT scanning. Each animal was evaluated in the early and later cerebritis stages of abscess evolution. On MR, the area of cerebritis enhanced after administration of Gd DTPA in a manner similar to that observed with contrast-enhanced CT. However, contrast enhancement was greater on the MR examination. Early lesions in two animals were detected only with contrast-enhanced MR imaging. This experience suggests that intravenously administered agents such as Gd DTPA should increase the diagnostic potential of MR imaging in neurologic diseases, especially those altering the blood-brain barrier.