Optimization of parameter values for complex pulse sequences by simulated annealing: Application to 3D MP-RAGE imaging of the brain

A number of pulse sequence techniques, including magnetization-prepared gradient echo (MP-GRE), segmented GRE, and hybrid RARE, employ a relatively large number of variable pulse sequence parameters and acquire the image data during a transient signal evolution. These sequences have recently been proposed and/or used for clinical applications in the brain, spine, liver, and coronary arteries. Thus, the need for a method of deriving optimal pulse sequence parameter values for this class of sequences now exists. Due to the complexity of these sequences, conventional optimization approaches, such as applying differential calculus to signal difference equations, are inadequate. We have developed a general framework for adapting the simulated annealing algorithm to pulse sequence parameter value optimization, and applied this framework to the specific case of optimizing the white matter-gray matter signal difference for a T₁-weighted variable flip angle 3D MP-RAGE sequence. Using our algorithm, the values of 35 sequence parameters, including the magnetization-preparation RF pulse flip angle and delay time, 32 flip angles in the variable flip angle gradient-echo acquisition sequence, and the magnetization recovery time, were derived. Optimized 3D MP-RAGE achieved up to a 130% increase in white matter-gray matter signal difference compared with optimized 3D RF-spoiled FLASH with the same total acquisition time. The simulated annealing approach was effective at deriving optimal parameter values for a specific 3D MP-RAGE imaging objective, and may be useful for other imaging objectives and sequences in this general class.     

Septal-lateral annnular cinching perturbs basal left ventricular transmural strains.

OBJECTIVE: Septal-lateral annular cinching ('SLAC') corrects both acute and chronic ischemic mitral regurgitation in animal experiments, which has led to the development of therapeutic surgical and interventional strategies incorporating this concept (e.g., Edwards GeoForm ring, Myocor Coapsys, Ample Medical PS3). Changes in left ventricular (LV) transmural cardiac and fiber-sheet strains after SLAC, however, remain unknown. METHODS: Eight normal sheep hearts had two triads of transmural radiopaque bead columns inserted adjacent to (anterobasal) and remote from (midlateral equatorial) the mitral annulus. Under acute, open chest conditions, 4D bead coordinates were obtained using videofluoroscopy before and after SLAC. Transmural systolic strains were calculated from bead displacements relative to local circumferential, longitudinal, and radial cardiac axes. Transmural cardiac strains were transformed into fiber-sheet coordinates (X(f), X(s), X(n)) oriented along the fiber (f), sheet (s), and sheet-normal (n) axes using fiber (alpha) and sheet (beta) angle measurements. Results: SLAC markedly reduced (approximately 60%) septal-lateral annular diameter at both end-diastole (ED) (2.5+/-0.3 to 1.0+/-0.3 cm, p=0.001) and end-systole (ES) (2.4+/-0.4 to 1.0+/-0.3 cm, p=0.001). In the LV wall remote from the mitral annulus, transmural systolic strains did not change. In the anterobasal region adjacent to the mitral annulus, ED wall thickness increased (p=0.01) and systolic wall thickening was less in the epicardial (0.28+/-0.12 vs 0.20+/-0.06, p=0.05) and midwall (0.36+/-0.24 vs 0.19+/-0.11, p=0.04) LV layers. This impaired wall thickening was due to decreased systolic sheet thickening (0.20+/-0.8 to 0.12+/-0.07, p=0.01) and sheet shear (-0.15+/-0.07 to -0.11+/-0.04, p=0.02) in the epicardium and sheet extension (0.21+/-0.11 to 0.10+/-0.04, p=0.03) in the midwall. Transmural systolic and remodeling strains in the lateral midwall (remote from the annulus) were unaffected. CONCLUSIONS: Although SLAC is an alluring concept to correct ischemic mitral regurgitation, these data suggest that extreme SLAC adversely effects systolic wall thickening adjacent to the mitral annulus by inhibiting systolic sheet thickening, sheet shear, and sheet extension. Such alterations in LV strains could result in unanticipated deleterious remodeling and warrant further investigation.     

Impact of Increasing Margin Around the Lumpectomy Cavity to Define the Planning Target Volume for 3D Conformal External Beam Accelerated Partial Breast Irradiation

The purpose of this study was to evaluate the dose to normal tissues as a function of increasing margins around the lumpectomy cavity in accelerated partial breast irradiation (APBI) using 3D-conformal radiotherapy (3DCRT). Eight patients with Stage 0-I breast cancer underwent treatment planning for 3DCRT APBI. The clinical target volume (CTV) was defined as a 15-mm expansion around the cavity limited by the chest wall and skin. Three planning target volumes (PTV1, PTV2, PTV3) were generated for each patient using a 0, 5-, and 10-mm expansion around the CTV, for a total margin of 15, 20, and 25 mm. Three treatment plans were generated for every patient using the 3 PTVs, and dose-volume analysis was performed for each plan. For each 5-mm increase in margin, the mean PTV:total breast volume ratio increased 10% and the relative increase in the mean ipsilateral breast dose was 15%. The mean volume of ipsilateral breast tissue receiving 75%, 50%, and 25% of the prescribed dose increased 6% to 7% for every 5 mm increase in PTV margin. Compared to lesions located in the upper outer quadrant, plans for medially located tumors revealed higher mean ipsilateral breast doses and 20% to 22% more ipsilateral breast tissue encompassed by the 25% IDL. The use of 3DCRT for APBI delivers higher doses to normal breast tissue as the PTV increases around the lumpectomy cavity. Efforts should be made to minimize the overall PTV when this technique is used. Ongoing studies will be necessary to determine the clinical relevance of these findings.     

The emergence of GABA-accumulating neurons during retinal histogenesis in the embryonic chick

The emergence of GABA-accumulating neurons was studied from stages 29 to 40 during retinal histogenesis in the chick, covering embryonic (E) days E6-E14, using autoradiographic analysis following incubation of isolated retinas with [3H]GABA (2 microM). Analysis was restricted to central retina which is more advanced in its differentiation than the periphery. On E6 numerous mitotic figures were present along the scleral border of the unstratified neuroepithelium. Specific localization of [3H]GABA was associated initially with somata situated in middle regions of the retinal expanse. Occasionally contiguous pairs of labeled cells were seen. The inner plexiform layer makes its appearance during E7; at that time silver grains were present over cell bodies located in the ganglion cell layer and the proximal portion of the inner nuclear layer, those of probable amacrine cells. As retinal stratification continued, more cells were observed to have elaborated membrane systems for GABA uptake with varying degrees of affinity. By E8, although dividing, non-labeled cells were in close proximity, GABA-labeled cells were observed in positions of horizontal cells. By E14, the pattern of label distribution appeared essentially similar to that reported for adult retina, i.e. [3H]GABA labeling was observed over horizontal cells and their processes, subpopulations of amacrine cells which appear to ramify extensively across the inner plexiform layer, selected perikarya of the ganglion cell layer, and the nerve fiber layer. In addition, a subpopulation of labeled photoreceptors, some identified as cones by virtue of oil droplets, was observed. Thus, preferential accumulation of GABA appears during E6, prior to formation of either inner or outer plexiform layers. The localization of [3H]GABA demonstrates that ganglion and amacrine cell bodies are labeled initially, followed by horizontal cells. Specific accumulation of [3H]muscimol, a potent agonist of GABA receptors, appears about E12 over cells located in proximal regions of the inner nuclear layer; these somata later ramify in sublaminae 2 and 4 of the inner plexiform layer.     

Single,mediastinal, unilobar lung -a rare form of subtotal pulmonary agenesis

We describe a case of a full-term infant with severe respiratory failure and pulmonary insufficiency caused by an anomaly consisting of a single, unilobar lung arising from the trachea and situated in the middle mediastinum. Plain film, echocardiogram, and surgical aspects will be described and correlated with the post mortem findings and embryologic considerations. We were unable to find a similar case reported in the literature and conclude that this rare lesion represent an intermediate form between total and unilateral pulmonary agenesis. Presented at the Society for Pediatric Radiology, Washington D.C. 12 April 1986