Establishing a Thermal Imaging Technology (IRT) Based System for Evaluating Rat Erectile Function

Abstract

Introduction: Measurement of intra-cavernous pressure (ICP) is an internationally recognized method to evaluate erectile function of animals, however, this process is invasive, destructive, and cannot be repeated, leading to a daunting challenge for monitoring the changes in erectile function throughout the whole treatment duration.

Aim: To verify whether infrared ray thermography technology based system could be a good substitution of ICP for evaluating rat erectile function.

Methods: A novel thermal image-based method, infrared ray thermography technology (IRT) was employed to monitor erectile function in erectile dysfunction (ED) rats. To detect the sensitivity and specificity of this new technology, 4 ED rat models (Diabetic, nerve-injury, vascular-injury and aged ED models) were established and subjected to both ICP and IRT test.

Outcomes: Statistical comparisons were done to test the effectiveness of this new way for detecting and dynamically monitoring erectile function.

Results: Based on the data curves obtained from ICP and IRT, the IRT showed a similar trend (including peak value, climbing speed) as that of ICP. IRT is considered as a precise way to monitor the real-time changes of erectile function in all ED rat models. The AUC of peak temperature detected by IRT in DMED, aged ED, vascular-injury ED, the nerve-injury ED and total ED rat models were 0.9811,0.9836,0.9893,0.9989 and 0.9882, respectively. Meanwhile, the AUC of temperature climbing rate were 0.6486,0.8357,0.9184,0.8675and 0.8168.Also,it is a non-invasive process of dynamically monitoring erectile function of a same rat at different time points (before and after drug intervention). The data showed that the real-time recovery by tadalafil was obtained by IRT methods even after treatment for only 2 weeks in the diabetic ED (DMED) rat model.

Conclusion: A novel noninvasive method for monitoring erectile function in rat ED models was established, and can replace or supplement ICP test. Liu S, Zhao Z, Wang Z et al. Establishing a Thermal Imaging Technology (IRT) Based System for Evaluating Rat Erectile Function. Sex Med 2022;10:100475.

Keywords: Erectile Dysfunction; Infrared Ray Thermography Technology; Intra-Cavernous Pressure.

Figure 1

Schematic diagram of intra-cavernous pressure (ICP) test and infrared thermography technology (IRT) detection. A: Schematic diagram of ICP detection. The erection of rat was stimulated by electrophysiological instrument MAP and ICP was measured after aorta intubation and penile intubation, causing irreversible damage (TN1012/ST Pulse Transducer, ML4856, ADINSTRUMENTS Australia). The CN stimulation parameters were shown. B: Schematic diagram of IRT detection. The thermal imager was placed 25 cm away from the rat penis, and a thermometer was inserted into the rat rectum to normalize individual variation; C: Instruments of IRT detection were shown. ①respiratory anesthesia machine pumps 3% isoflurane. ②thermal image ③rectal thermometer ④constant temperature rat platform and ⑤anesthesia induction box.A real-time display interface of IRT detection. Acquired by thermometer showing temperature focus based on rat penis, ranging from blue (flaccid condition) to red (erectile condition).

Figure 2

Automatic real-time curve was drawn according to the local penis temperature (automatic focusing). A:This operation interface showed dynamic monitoring of erectile procedures based onIRT test.Automatic focus were set to tracing a fixed location on pennis, and it could be correct in data analysis procedure by using supporting software(FLIR Tools+ 5.7, Sweden). B: Awholeprocedureof erectile wasrecorded, color from blue to red indicating a temperature climbing during this procedure; After the stimulation was removed, the color of focus area turned to blue, indicating a temperature decline. Changes in temperature and erection angle are synchronized in real time indicating a close relation between temperature and blood supply during procedure of erectile. More details can be found in supplementary data(video.wmv).

Figure 3

The establishment of 4 classic erectile dysfunction rat models. A. The establishment of DMED rat model was shown. a: Schematic diagram of establishment of diabetic rat model. After 8 weeks,>95% rats were confirmed suffering from erectile dysfunction; b: normal control rats; c: DM rats. Diabetic rats are more emaciated, with yellowish hair of no luster. B. The establishment of Nerve-injury ED rat model was shown. A:Schematic diagram of establishing a nerve injury model. The hemostat was applied with full tip closure to each CN 1 mm distal to the MPG for 2 minutes; >95% rats were confirmed with erectile dysfunction;b: The localization of cavernous nerve and MPG. C. The establishment of aged ED rat model. a: normal rat; b: aged rat. The aged rats were more obese with thin hair; c,d: Masson trichrome staining of penile midshaft specimens, and comparison to normal control rats (c), less actin and more collagen were confirmed in aged rats (d).>90% aged rats were confirmed with erectile dysfunction; D. The establishment of vascular-injury ED rat model. a: Schematic diagram of establishing vascular injury models. The microplastic soft catheter with a length of 2 mm was cut longitudinally with microsurgical scissors; the soft catheter (cuff) was carefully wrapped in the separated internal iliac artery with microsurgical forceps under the dissecting microscope, and then the fixed with a silk thread. After operation, the rats were fed with high-fat diet for 8 weeks post-surgery, >95% rats were confirmed with erectile dysfunction; b:operation of cuff placement; c,d: HE staining of internal iliac artery of normal rats (c) and vascular-injury rats (d). The intima of vessels with cuff was thickened and the lumen became narrow.

Figure 4

Comparison of curve graph of IRT and ICP based on real-time data gained from Normal controland 4 ED models. The erectile procedures were stated by CN stimulation as described above; the ICP/MAP data were obtained by electrophysiological instrument; the temperature was monitored by thermal imager, a thermometer was inserted into the rectum of the rats to normalize individual variation. After removing the stimulation, the ICP and temperature were gradually returned to baseline. A. Normal control rats; B,C: DMED models; D,E: Aged ED models; F,G: vascular-injury ED models; H,I: nerve-injury ED models.

Figure 5

ROC curve and spearman correlation analysis of different models. A(a,b): The ROC curve of peak temperature and temperature climbing rate in total rats; A(c,d): the scatter diagram of spearman correlation analysis between the values detected by IRT and the values detected by ICP in total rats; B(a,b): the ROC curve of peak temperature and temperature climbing rate in DMED models; B(c,d): the scatter diagram of spearman correlation analysis between the values detected by IRT and the values detected by ICP in DMED models; C(a,b): the ROC curve of peak temperature and temperature climbing rate in nerve-injury ED models; C(c,d): the scatter diagram of spearman correlation analysis between the values detected by IRT and the values detected by ICP in nerve-injury ED models; D(a,b): the ROC curve of peak temperature and temperature climbing rate in vascular-injury ED models; C(c,d): the scatter diagram of spearman correlation analysis between the values detected by IRT and the values detected by ICP in vascular-injury ED models; E(a,b): the ROC curve of peak temperature and temperature climbing rate in aging ED models; E(c,d): the scatter diagram of spearman correlation analysis between the values detected by IRT and the values detected by ICP in aging ED models.

Figure 6

Application of IRT in real-time observation for improving erectile function in a single laboratory animal. A: Experimental design schema. Long-term monitoring of erectile function was conducted by IRT. Four weeks after STZ injection, DMED in rats was confirmed by thermal imager. During the next 6 weeks, tadalafil was orally given every day at a dose of 5mg/kg. The erectile function of rats was detected by IRT after administration of apomorphine; B: Real-time observation of improved erectile function on a single DMED rat after treatment. C: Penile/Rectal temperature rates exhibited by real-time curves to reflex the improvement of erectile function. D,E: 10 independent experiments were conducted and data was taken into statistical graph. Peak T of penile:Peak temperature of rat's penile. Rate of T rise: Speed of temperature climbing= (Peak temperature –Lowest temperature of penile)/ time consumed. * P<.05, we compare the multiple groups by the one-way repeated measures anova through SPSS 25.0.