Wallace W. Peck

Cardiac tumors: assessment with Gd-DTPA enhanced MR imaging.

Previous studies have shown the value of MR imaging for the identification of cardiac masses. The distinction of intramural tumors from normal myocardium may be equivocal because of the similarity of signal intensity between tumor and normal myocardium on ECG-gated SE images. The purpose of this study was to assess the role of Gd-DTPA for improving the contrast between cardiac tumors and myocardium. Four patients with established or suspected cardiac tumors were imaged with a 1.5 T imager. The T1-weighted images (TR = RR interval, TE = 20-30 ms) were obtained before and immediately after the intravenous injection of Gd-DTPA, at a dosage of 0.1 mmol/kg. Tumors were identified in three patients. All tumors were isointense to the myocardium in precontrast images but demonstrated differential enhancement relative to myocardium after the administration of Gd-DTPA. Two tumors were hyperintense relative to myocardium, and the third was mostly hypointense, surrounded by a hyperintense rim. In the remaining case, no tumor was found and the myocardium was homogeneously enhanced on postgadolinium images. Gadolinium DTPA can produce differential enhancement of tumor from normal myocardium and therefore demonstrate intramural masses.

Perfluoroctylbromide as a blood pool contrast agent for liver, spleen, and vascular imaging in computed tomography.

Perfluoroctylbromide (PFOB) in emulsion form was tested as a blood pool imaging agent for computed tomography (CT) in five animals (three dogs and two pigs). Computed tomography of the kidneys, liver, spleen, and mediastinum was performed in the control state and at various time intervals after the end of PFOB infusion. The attenuation coefficient of the vascular space increased by 117 Hounsfield units (HU) (range 105–128 HU), the liver by 54 HU (range 43–70 HU), and the spleen by 77 HU (range 69–86 HU) 30 to 50 min after the end of PFOB infusion, 5 ml/kg. The vascular space enhanced by 25 HU for every g of PFOB/100 ml of blood and remained at almost a constant level for hours after the end of infusion. In conclusion, PFOB emulsion, in addition to hepatosplenic enhancement, produces prolonged and substantial opacification of the vascular space, allowing CT imaging of the heart and vascular structures minutes to hours after the end of infusion.

Effects of Transient Coronary Ischemia and Reperfusion on Myocardial Edema Formation and In Vitro Magnetic Relaxation Times

The effects of transient ischemia and reperfusion on regional myocardial function, salvage and swelling have been systematically analyzed in experimental canine preparations. The results of these interventions on myocardial in vitro measurements of magnetic relaxation times (T1 = magnetization recovery, T2 = spin echo) are of significant importance with respect to future nuclear magnetic resonance tomographic imaging. Thus, using a pulsed magnetic resonance spectrometer (10.7 MHz), myocardial tissue samples from two groups of dogs were evaluated. In group 1 (n = six dogs), the left anterior descending artery was occluded for 3 hours before sacrifice; in group 2 (six dogs), 3 hours of occlusion was followed by 1 hour of reperfusion. Multiple tissue samples from normal and ischemic (or ischemic and reperfused) myocardium were obtained for measurement of T1, T2 and % water content (wet weight--dry weight/wet weight). Water content increased with ischemia (78 +/- 4%) and reperfusion (81 +/- 4%) (both p less than 0.01 versus control values). Values for T1 increased with ischemia (598 +/- 39 versus 487 +/- 23 ms in normal tissue from the same heart, p less than 0.01). Even greater T1 changes occurred in the animals with reperfusion (654 +/- 52 ms, p less than 0.01 versus the intra-animal control values). Changes in T2 were similar but less marked (ischemic zone 43.9 +/- 1.0 versus 41.2 +/- 1.0 ms in nonischemic tissue in the corresponding heart, p less than 0.05; reperfusion zone 48.3 +/- 3.5 versus 41.9 +/- 2.3 ms in the normal zone, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo assessment by computed tomography of the natural progression of infarct size, left ventricular muscle mass and function after acute myocardial infarction in the dog

Quantification of myocardial infarct (MI) size is of prognostic importance in patients with acute ischemic damage. Evaluation of the efficacy of interventions for salvage of ischemic myocardium depends on the accurate estimation of the ischemic area and a knowledge of the natural progression of the infarct. Computerized transmission tomography (CTT) is a reliable in vivo technique for estimating infarct size. We serially studied 8 dogs over approximately 1 month after occlusion of the left anterior descending coronary artery using both ungated and prospectively electrocardiogram-gated CTT. Scans were obtained 20 minutes after occlusion and then several more times until the dogs were killed. Using the ungated CTT scans, infarct size increased from 0 to 4 days (+ 65 +/- 20%, mean +/- standard error of the mean, p less than 0.05), then progressively decreased. The initial perfusion defect overestimated the eventual MI size at 1 month by 33 +/- 15% (p less than 0.05). The MI size at necropsy correlated well (r = 0.98, p less than 0.001) with CTT MI size determined just before sacrifice. Non-infarcted left ventricular (LV) muscle mass increased significantly (27 +/- 7% greater at 1 month compared with day 0, p less than 0.01) over time, presumably representing compensatory LV hypertrophy. The LV muscle mass at necropsy correlated well (r = 0.94, p less than 0.001) with CTT LV muscle mass just before sacrifice.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary density distribution in experimental noncardiac canine pulmonary edema evaluated by computed transmission tomography.

We evaluated the density distribution (anterior-posterior) of the right lung in 19 acutely anesthetized supine dogs using computed transmission tomography (CTT). Eleven dogs served as controls, and eight received 0.12 cc/kg of intravenously administered oleic acid. The latter were sequentially imaged over 1 hour. Nine of these dogs (three control and six oleic acid dogs) had wet weight/dry weight ratios of the corresponding anterior and posterior lung sections evaluated immediately upon completion of the scans. In the control animals, the posterior (dependent) lung was 25 +/- 8% (+/- S.D.) denser than the anterior lung, and did not differ if a second section of the lung was evaluated (1 cm cranial or caudal), or if the animal was imaged on a second day (n = 6). In the oleic acid dogs, the posterior portion of the lung was significantly denser 10 minutes after injection of oleic acid (P less than 0.05), and almost twice as dense 1 hour after initial injection. The density changes determined by CTT in the anterior and posterior lung zones correlated well with the increasing regional wet weight/dry weight relationships determined from the lung on postmortem exam (r = 0.90). We conclude that early subtle density changes in the posterior lung can be found in oleic acid injury pulmonary edema. This can be easily quantitated using CTT, and may prove useful in following physiologic and therapeutic interventions during leaky membrane acute pulmonary injury.

Analysis of phase-angle histograms from equilibrium radionuclide studies: Correlation with semiquantitative grading of wall motion

Quantitative wall motion assessment from gated radionuclide left ventriculograms using phase analysis was studied in 14 subjects (6 normal volunteers and 8 patients with previous acute myocardial infarction). The standard deviation and skewness of the phase-angle histograms were determined from both global and segmental left ventricular (LV) regions of interest (septal, apical and posterolateral). Studies were performed at rest, after administration of atropine and after combined administration of phenylephrine and atropine. Both the standard deviation and skewness showed significant correlations with semiquantitative wall motion scoring. From the global analyses, the highest correlations were found after atropine administration (r = 0.86, p less than 0.001 for standard deviation and r = 0.72, p less than 0.001 for skewness). Nevertheless, deterioration in global wall motion scores correlated poorly with directional changes in standard deviation (r = 0.06, difference not significant) or skewness (r = 0.33, p less than 0.05). No significant correlation between skewness or change in skewness and wall motion scores were found with the segmental analyses. The maximal correlation between segmental standard deviation and segmental wall motion grading was again noted after atropine administration (r = 0.68, p less than 0.001), but deterioration in grading did not correlate with similar deterioration of the standard deviation (r = -0.05, difference not significant). Based on 90% confidence limits for normal standard deviation and skewness, an abnormal standard deviation (greater than 14.5) identified 13 of 28 wall motion disorders (sensitivity 46%), whereas an abnormal skewness (greater than 1.4) identified 1 of 28 wall motion disorders (sensitivity 4%).(ABSTRACT TRUNCATED AT 250 WORDS)

MR of soft tissue chloroma in a patient presenting with left pubic and hip pain

A patient with a history of chronic granulocytic leukemia presented with hip and pubic pain. Magnetic resonance study showed a mass infiltrating the obturator externus muscle, which was biopsied under CT guidance. Pathology of the mass was chloroma. Magnetic resonance can be extremely valuable in determining the etiology of hip and pubic pain in patients with a history of leukemia.

Perfluoroctylbromide: Acute Hemodynamic Effects, in Pigs, of Intravenous Administration Compared With the Standard Ionic Contrast Media

Perfluoroctylbromide (PFOB) is a relatively new noniodinated contrast media that, after intravenous administration, produces prolonged opacification of the blood pool and subsequently selectively enhances the liver and spleen on computed tomography. There has been concern regarding the hemodynamic effect of this agent but little actual knowledge exists in this regard. Accordingly, the acute transient hemodynamic effects of PFOB emulsion were evaluated in five pigs and compared with the standard ionic contrast agent meglumine sodium diatrizoate (Renografin-76). Left ventricular (LV) pressure, internal diameter, and wall thickness were monitored during the alternate intravenous administration of 930 mg/ml PFOB and 370 mg/ml R-76 at a rate of 20 mls/second for a total volume of 1 ml/kg body weight. Renografin-76 caused a significant decrease in LV pressure and dp/dt (rate of change of LV pressure), and an increase in LV end-systolic diameter and a decrease in LV end-diastolic wall thickness. PFOB caused no change in LV pressure and dimensions. Thus, rapid intravenous administration of PFOB does not induce significant acute alterations in left ventricular pressure, dp/dt, dimension, or wall thickness.

Use of computerized tomography to assess myocardial infarct size and ventricular function in dogs during acute coronary occlusion and reperfusion

Prospectively ECG-gated and nongated computed tomography (CT) can be used to assess global and regional left ventricular (LV) function and to measure myocardial infarct (MI) size. In the current study, CT was used to assess the effects of coronary occlusion and reperfusion in 16 dogs. Ten dogs were subjected to permanent occlusion of the proximal left anterior descending coronary artery and 6 dogs were reperfused after a 2-hour period of total coronary occlusion. Gated scans were used to quantitate the extent of wall thickening in the ischemic zone and to assess changes in mid-LV cross-sectional chamber area at end-diastole and end-systole. Nongated scans were used to estimate the size of the initial perfusion defect during contrast injection shortly after coronary occlusion and the size of the MI as indicated by delayed enhancement of the infarct 10 to 30 minutes after cessation of contrast administration. Neither group showed significant changes in end-diastolic chamber area during acute occlusion or 3 days later. Both groups showed a significant deterioration in percent change in chamber area both early after coronary occlusion and 3 days later; however, in the permanent occlusion group, percent wall thickening in the ischemic zone decreased from 46.2 +/- 16.5% (mean +/- standard deviation) to 1.6 +/- 9.0% during acute occlusion (p less than 0.01) and thickening remained depressed 3 days later (2.4 +/- 10.1%, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacologically induced changes in wall thickening dynamics and mid-ventricular volumes in dogs assessed by prospectively gated computed tomography

Abstract Assessment of regional wall thickening dynamics is important for monitoring the response of normal and ischemic myocardium to pharmacologic interventions. Because regional wall thickness can be measured on computed tomographic (CT) scans of the heart, the ability of electrocardiogram-gated computed tomography to determine the effects of pharmacologic agents on global and segmental left ventricular (LV) function was assessed. Eight conditioned dogs were studied at a control state and during drug-induced changes in contractility and loading conditions brought about by the use of isoproterenol (0.15 μg/kg/min), phenylephrine (0.3 μg/kg/min), and verapamil (0.2 mg/kg infused over 10 minutes). Ten contrast-enhanced CT slices (1 cm thick) at the same mid-LV level were reconstructed for each 10% of the R-R interval throughout an average cardiac cycle using prospectively gated CT scans. End-diastolic and end-systolic frames were selected and analyzed for the following: septal, apical, and lateral wall thickness, percent wall thickening, end-diastolic and end-systolic mid-LV volume, and percent change in mid-LV volume. During control, end-diastolic and end-systolic LV wall thicknesses (in millimeters) were 12 ± 2 and 15 ± 2 for the septal wall, 8 ± 1 and 11 ± 2 for the apical wall, and 10 ± 1 and 12 ± 1 for the lateral wall, respectively. The percent thickening in these respective segments was 24 ± 8, 36 ± 10, and 28 ± 13. The control end-diastolic and end-systolic mid-LV volumes were 16 ± 3 and 12 ± 3 ml, resulting in a percent change of 27 ± 7%. Phenylephrine induced significant thinning of the walls and impairment of systolic thickening, whereas isoproterenol induced opposite effects. Verapamil produced a significant decrease in mean blood pressure (123 ± 9 versus 99 ± 23 mm Hg, p