Direct digital subtraction

Compared with cut-film selective intra-arterial catheter angiography recorded directly on to X-ray film, intra-arterial digital subtraction angiography (DSA) (Fig. 12.1) is quicker the images are easier to manipulate and store and contrast resolution is better although spatial resolution is less. However, there is no evidence that less contrast is used or that it is much safer (Warnock et al. 1993). Even for imaging only as far as the carotid bifurcation. 

X-ray diffraction analysis showed that poly(ethylene 2,6-naphthalate) (PEN) film, annealed from 160 to 260 C crystallised in the alpha-crystal form, whilst crystallisation directly from the melt yielded the beta-crystal form when the crystallisation temperature (Tc) was greater than 200 C, and in the alpha form at lower Tc. Infrared spectra from PEN samples containing alpha, beta, and amorphous phases were determined, and the amorphous contribution digitally subtracted to yield characteristic spectra of the amorphous, alpha, and beta phases. It is proposed that the alpha crystal form adopts an all-trans conformation, whilst the beta crystal form adopts a conformation with appreciable gauche character. Conformational changes in PEN occurred due to the rotation of the naphthalene ring as well as rotation of the ethylene glycol units. The... 

In bone lesions that are assumed to be extremely hy-pervascularized such as suspected metastases of renal cell carcinoma, a digital subtraction angiography may have to be obtained prior to biopsy. Transarterial embo-hzation or direct puncture of the lesion with injection of absorbable gelatin sponge or polyvinyl alcohol particles helps to prevent serious hemorrhage when samples of the lesion are taken. 

Because atomic absorption enables direct analysis without the need of a concentration step it held promise for metals ranging from 0.1 to 1 ppm. Table 8.6 shows the absorbances obtained for nickel in a synthetic unknown prepared from Boscan crude by the method of Slavin and Trent. An air-acetylene flame afforded convenient combustion, and absorption at the 2316 non-absorbing line was subtracted from the sample absorbance observations to correct for background absorption. The observations were made at the 100 average mode using the Nixie tube digital readout. 

Since q, T, and q are known, we determine R from the measurement of t. Actually, most commercial software calculate the size assuming that the object is spherical. As mentioned before, the digital correlator gives directly G2(q, t), and therefore, after subtracting the baseline and dividing by baseline, we get by the Siegert relationship a correlation function C(t) given by... 

Fig. 3. IB CRLAS apparatus, nable infrared laser radiation U coupled into the ring-down cavity. The light transmitting the output mirror is focused into an InSb detector. The resulting signal is amplified, digitized, and sent to a PC where it is fit to a firsi order exponential, which is directly related to the total cavity loss per laser pass. The PC additionally controls the scanning of the dye laser. Base line losses are determined by scanning the laser with the expansion turned off and are then subtracted from the data, yielding the absolute sample absorbance, from which the carrier concentrations are extracted." ...

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