Margaret A. Douglas

A Fourier based algorithm for tracking SPAMM tags in gated magnetic resonance cardiac images

A method is described for automatically tracking spatial modulation of magnetization tag lines on gated cardiac images. The method differs from previously reported methods in that it uses Fourier based spatial frequency and phase information to separately track horizontal and vertical tag lines. Use of global information from the frequency spectrum of an entire set of tag lines was hypothesized to result in a robust algorithm with decreased sensitivity to noise. The method was validated in several ways: first, actual tagged cardiac images at end diastole were deformed known amounts, and the algorithms predictions compared to the known deformations. Second, tagged, gated images of the thigh muscle (assumed to have similar signal to noise characteristics as cardiac images, but to not deform with time) were created. Again the algorithmic predictions could be compared to the known (zero magnitude) deformations and to thigh images which had been artificially deformed. Finally, actual cardiac tagged images were acquired, and comparisons made between manual, visual, determinations of tag line locations, and those predicted by the algorithm. At 0.5 T, the mean bias of the method was < 0.34 mm even at large deformations and at late (noisy) times. The standard deviation of the method, estimated from the tagged thigh images, was < 0.7 mm even at late times. The method may be expected to have even lower error at higher field strengths.

Recruitment experience in the African American Study of Kidney disease and hypertension (AASK) pilot study

Several approaches for recruitment of African American adults with renal insufficiency due to hypertension (glomerular filtration rate between 25 and 70 ml/min/1.73 m2) were explored in the Pilot Study for the African American Study of Kidney Disease and Hypertension (AASK). Over a period of 42 weeks, prescreening information was obtained on 2880 individuals, of whom 498 (17%) were evaluated at a screening visit. Two hundred and twenty-five (8%) had an 125I-iothalamate assessment of glomerular filtration rate. Ninety-four of 97 participants who met all the study eligibility criteria were enrolled in the trial. The most common reasons for ineligibility during screening were absence of renal insufficiency or hypertension, presence of diabetes mellitus, and a body mass index above the acceptable level. Overall, an average of 31 prescreen contacts and 8 screening visits were conducted for every randomization (3.3% yield from prescreening to randomization). Screening in clinical practice was the most efficient method for recruitment (12.6% yield from prescreen contact to randomization compared to 1.1% from mass mailing campaigns, 1.3% from mass media campaigns, and 1.7% from referrals by patients with end-stage renal disease). Randomization yields increased with progressively higher age ranges (2.4%, 3.3%, and 6.0% prescreen to randomization yields for those aged < or = 50, 51-60, and 61-70, respectively). A slight majority (51%) of the prescreen contacts were women, but 75% of the randomized participants were men. Our results suggest that clinic-based screening is an effective approach for recruitment of African Americans with hypertension and renal insufficiency into clinical trials. They also suggest that enrollment of African American women in such studies is a special challenge.

The Measurement of Left Ventricular Function and the Detection of Wall Motion Abnormalities with High Temporal Resolution Ecg-Gated Scintigraphic Angiocardiography

An ECG-gated, scintigraphic imaging procedure is described in which a complete, average cardiac cycle is visualized with high temporal resolution. The ability of this method to detect wall motion abnormalities and quantitate left ventricular function is illustrated in a patient with severe coronary artery disease. These results are compared to (contrast) angiographic findings in the same patient.

Appointment attendance, pill counts, and achievement of goal blood pressure in the African American Study of Kidney disease and hypertension pilot study

The African American Study of Kidney Disease and Hypertension (AASK) Pilot Study evaluated the feasibility of conducting a 7-year clinical trial to assess the effect of two levels of blood pressure control based on mean arterial pressure (MAP) (low goal < or = 92 mm Hg or usual goal of 102-107 mm Hg) and three antihypertensive drug regimens (atenolol, amlodipine, or enalapril) as initial therapy in slowing the decline of renal function in African Americans with clinically diagnosed hypertensive nephrosclerosis. Ninety-four African American men and women between 18 and 70 years of age were randomized and followed for an average of 4.6 months. On average participants attended 87.5% of the scheduled monthly follow-up visits and achieved an acceptable level of medication adherence (80%-100% of prescribed doses by pill count) at 65.4% of those visits Blood pressure levels within goal were observed in 17.5% and 25.6% of the participants in the low- and usual MAP goal groups, respectively. Neither attendance nor medication adherence by pill count was associated with attainment of goal blood pressure. Although AASK Pilot Study participants maintained excellent attendance, their pill counts were lower than previously reported among clinical trial participants and goal blood pressure levels were difficult to achieve during the short period of follow-up.

Use of a video system in the study of ventricular function in man

A video-based system is described that determines ventricular volume from cineangiograms by automated border recognition or by manually assisted video planimetry. Analog circuits are utilized to provide on-line volume calculations. A computer system is used to calculate complex indexes of ventricular function from simultaneously obtained pressure and volume data. Although the system requires considerable effort to establish, it has many potential applications.

Fourier Filtering Cardiac Time Activity Curves: Sharp Cutoff Filters

Several problems may occur when analyzing cardiac left ventricular (LV) time activity curves (TACs) using the techniques of Fourier analysis. These difficulties are of course not unique to cardiac TACs, but rather are representative of the general problems encountered when applying Fourier analysis to discrete, sampled data. In the case of LV TAC’s created from equilibrium gated blood pool studies, one usually applies Fourier analysis in an attempt to filter counting statistical noise from the data. One of the common methods employed to accomplish this goal (albeit probably the least justified) is to Fourier transform the TAC into the frequency domain, filter the data with a sharp cutoff filter (i.e. multiplication in the frequency domain with a rectangular pulse) and invert the filtered data. The reason for the choice of a rectangular cutoff filter is usually simplicity. Whatever the reason, using a sharp cutoff in the frequency domain is identical to describing the data by a truncated Fourier series. Thus one is able to skip the Fourier transform step and instead directly calculate only those first few Fourier coefficients one is interested in. Several concerns need to be addressed. First, are the two constraints of the sampling theorem satisfied? That is, is the underlying TAC which has been sampled by the gated equilibrium procedure band limited, and if so is the sampling rate adequate (at least equal to the Nyquist rate).

Multimodality radiological image processing system (MRIPS)/MEDx: a system for medical image processing

A new image processing system, MRIPS/MEDx, is being deployed at NIH to facilitate the visualization and analysis of multidimensional images and spectra obtained from different radiological imaging modalities.