The goal of this work is to highlight those unique aspects of contrast-enhanced diagnostic optical imaging (OI) that
favor a broad clinical utilization of this emerging diagnostic technique and to illustrate certain identified challenges
opposing the enthusiastic clinical welcome for the OI method. We consider the single most appealing feature of OI to be
its much-touted exquisite sensitivity for the detection of near-infrared fluorescing (NIRF) probes, a sensitivity
supporting the development of disease- and molecule-specific NIR diagnostic probes, akin to nuclear imaging but
without the ionizing radiation and with superior spatial resolution. But a qualitative OI diagnostic examination, merely
defining the presence or absence of NIRF signal, may not be sufficient. The signal must be measurable. A quantitative
OI examination, capable of accurately assaying the tissue concentration of the fluorescing probe and changes in that
probe concentration related to disease progression or treatment would be extremely valuable. We discuss here at least
three challenges to quantitative diagnostic OI, a non-linear relationship between probe concentration and signal
intensity, background signal in the form of tissue auto-fluorescence, and the requirement to define precise location and
depth of the signal origin from within the subject.
Benign and malignant mammary tumors were induced in rats using a potent carcinogen, N-ethyl-N-nitrosurea (ENU). Induced tumors were examined under near-infrared (NIR) fluorescence imaging (excitation wavelength 670 to 730 nm, detection wavelength 750 and 800 nm) to search for a difference in the photophysical properties of the tumors reflecting their pathologic status. Three benign and eight malignant tumors were examined optically and pathologically. The non-enhanced optical images showed a significantly lower (P<0.05) spontaneous fluorescent signal in the benign tumors than in their malignant counterparts. The precise chemical origin for the observed differences in tumor autofluorescence remains undetermined. It can be hypothesized that the reported high concentration of porphyrins, NIR-fluorescing compounds, in the malignant lesions, could account for the observed increased autofluorescence.
A clinical comparison of computed radiography (CR) versus screen-film for imaging the critically-ill neonate is performed, utilizing a modified (hybrid) film cassette containing a CR (standard ST-V) imaging plate, a conventional screen and film, allowing simultaneous acquisition of perfectly matched CR and plain film images. For 100 portable neonatal chest and abdominal projection radiographs, plain film was subjectively compared to CR hardcopy. Three pediatric radiologists graded overall image quality on a scale of one (poor) to five (excellent), as well as visualization of various anatomic structures (i.e., lung parenchyma, pulmonary vasculature, tubes/lines) and pathological findings (i.e., pulmonary interstitial emphysema, pleural effusion, pneumothorax). Results analyzed using a combined kappa statistic of the differences between scores from each matched set, combined over the three readers showed no statistically significant difference in overall image quality between screen- film and CR (p equals 0.19). Similarly, no statistically significant difference was seen between screen-film and CR for anatomic structure visualization and for visualization of pathological findings. These results indicate that the image quality of CR is comparable to plain film, and that CR may be a suitable alternative to screen-film imaging for portable neonatal chest and abdominal examinations.
The clinical utility of computed radiography (CR) versus screen-film for neonatal intensive care unit (ICU) applications is investigated. The latest versions of standard ST-V and high- resolution HR-V CR imaging plates were compared via measurements of image contrast, spatial resolution and signal-to-noise. The ST-V imaging plate was found to have equivalent spatial resolution and object detectability at a lower required dose than the HR-V, and was therefore chosen as the CR plate to use in clinical trials in which a modified film cassette containing the CR imaging plate, a conventional screen and film was utilized. For 50 portable neonatal chest examinations, plain film was subjectively compared to the perfectly matched, simultaneously obtained CR hardcopy and softcopy images. Grading of overall image quality was on a scale of one (poor) to five (excellent). Readers rated the visualization of various structures in the chest (i.e., lung parenchyma, pulmonary vasculature, tubes/lines) as well as the visualization of pathologic findings. Preliminary results indicate that the image quality of both CR soft and hardcopy are comparable to plain film and that CR may be a suitable alternative to screen-film imaging for portable neonatal chest x rays.