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A comparison between portable ultrasound (MIDUS) and nocturnal RigiScan when confirming the diagnosis of vascular organic erectile disorder


In recent years, the use of RigiScan and ultrasound to assess erectile dysfunction has fallen from favour. However, in a small minority of specialist cases, where a vascular, neurogenic or psychogenic aetiology requires confirmation, there remains a need for further investigation. To establish if in a preliminary assessment the use of nocturnal RigiScan or male impotence diagnostic ultrasound system (MIDUS) represents best practice as a diagnostic investigation in patients with a history suggestive of vascular organic erectile disorder. Men attending both urological and psychosexual therapy clinics with erectile dysfunction were assessed using a generic assessment schedule. Patients with a history suggestive of vascular erectile disorder were offered the opportunity of dual investigation of their condition. After screening using a provocative RigiScan using visual stimuli that gleaned inconclusive results, patients were offered the chance to enter a study with both nocturnal RigiScan and MIDUS investigation. These were confined for the purposes of this study to RigiScan events, peak systolic flow velocity (PSV) and end-diastolic flow velocity (EDV) from ultrasound examination where an abnormal EDV is defined as in excess of 4.5 cm/s and a normal PSV is variously defined as being greater than 35 cm/s. In all, 38/43 (88%, 95% CI: 76–95%) of men had a nocturnal event exceeding 3 min on the RigiScan investigation. This compares with 17/43 (40%, 95% CI: 26–54%) of men with a normal EDV blood flow of less than 4.5 cm/s (P<0.017) and 32/43 (74%, CI: 60–85%) of men with a normal PSV flow greater than 35 cm/s (NS). Rigiscan and ultrasonography of the cavernosal vessels are of equal usefulness in suspected arterial penile disease although where veno-occlusive disease is suspected, ultrasonography is more specific.


The introduction of sildenafil has simplified the management of erectile dysfunction for many affected men. However, young men presenting with pelvic or perineal trauma1 or those insisting upon an unequivocal diagnosis prior to treatment, may require accurate assessment of the nature and cause of the erectile dysfunction.

A study comparing nocturnal penile tumescence (NPT) with penile Doppler ultrasonography and cavernosometry tests in a group of 87 consecutive patients found that of 50 patients diagnosed with vascular ED, 29 had arterial failure and 21 had veno-occlusive disorder. In the same group, NPT recording revealed vascular erectile dysfunction in 53 patients. Here, NPT showed 90.6% sensitivity and 88.2% specificity in differentiating the cause of erectile dysfunction. In the patients with a vascular cause, no difference was found between arterial and veno-occlusive dysfunction with regard to tip tumescence activity unit (TAU), base TAU, tip rigidity activity unit (RAU), base RAU and erection time.2

A thorough clinical assessment alongside the patient's own description of their erectile status should be sufficient. A study looking at the predictive value of the patients' own subjective assessment of early morning and nocturnal erections and the presence of vascular risk factors and cigarette smoking correlated well with the outcome of RigiScan and PSV (peak systolic velocity) during colour flow duplex Doppler ultrasonography.3 However, the patients' objective assessment of their own early morning erections was found to be unreliable. Nocturnal PTR correlated well with normal PSV but was not found to exclude organic ED. Of the subjects, 59% had an abnormal NPTR. Of these 15% continued to experience rigid morning erections and 29% had an abnormal PSV.

Thus, though a recent survey suggests that its use as a diagnostic test occurs in only some 3–4% of cases,2 NPT with RigiScan remains the gold standard in assessing penile rigidity. DDU allows for the evaluation of penile cavernosal blood vessels (Duplex) and blood flow (Doppler) in conjunction with vaso-dilator stimulation. These provide information about the intrapenile anatomy and are obtained by measuring both the changing calibre of the corporal arteries and blood flow through the penile vessels before and after a vaso-dilator injection to provide peak systolic and diastolic flows.

One possible alternative to both RigiScan and DDU is the male impotence diagnostic ultrasound system (MIDUS). Combined with a pharmacological provocation the MIDUS involves the application of a probe or transducer to the base of the penis. This gives a detailed, graphical read-out of blood velocity. In its portable state, MIDUS allows patients to have a diagnostic ultrasound within the clinic room and has been shown to be as diagnostically accurate as DDU.4 Although unable to generate the sort of 3D images of arteries as DDU, the MIDUS allows the clinician to obtain rapid velocity, wave-form measurements in both cavernosal arteries of the penis and gives the immediate benefit of shortening the delay in diagnosis.

Thus with the DDU considered out of reach for a proportion of clinicians it was the aim of this study to compare and contrast those systems most readily available that combine ease of use with a high degree of diagnostic accuracy. Concentrating on those patients with a suggested vascular aetiology plus a mid-way response on RigiScan monitoring (40–70%), it was our interest to show whether the next investigation of choice should be NPT using either RigiScan or portable MIDUS.


Prior to the study, men attending Porterbrook's specialist clinic for sexual problems and Sheffield's Royal Hallamshire's Urology OPD were assessed by specialist nursing and medical staff experienced in using standardised semistructured interview schedules designed to assess sexual, particularly erectile, dysfunction. Initially, the men were assessd to identify any risk factor that might suggest a vascular aetiology. This initial screen of 800 ED patients attending the clinic over a 12 month period identified those patients with possible risk of vascular compromise. The final study sample had all been positively assessed as having risk factors such as smoking, hypertension, diabetes mellitus, peripheral vascular disease or coronary heart disease and/or with a family history of such problems. This group were then further assessed using laboratory-administered visual stimuli and vibration in conjunction with RigiScan and intracavernosal injection (15 mcg alprostadil). The value of this intervention is unclear.5 Of this group, those patients with tip scores of less than 60% for under 3 min and/or base scores of less than 70% for under 3 min,3 were asked to give informed consent to enter the study. It was felt that as the men in this group remained without a definite diagnosis of aetiology, weight would be added to the comparison between the two assessment techniques. Nocturnal RigiScan is already recognised as a successful means of assessing the vascular component of ED at least where there is a positive response. If negative, further evaluation is necessary. If the MIDUS could perform as well as RigiScan in this group of patients then the comparison would be further enhanced.

Once consented the men were randomised into either NPT with RigiScan or for further assessment using the office-based MIDUS during which the patient received a 15 mcg, and if necessary a further 10 mcg, intracavernosal injection of alprostadil. After 1 week the subjects were crossed over to receive the alternative assessment.


In total, 60 patients were recruited into this study. The analysis is based on the 43 subjects who completed both the nocturnal RigiScan and MIDUS assessments. The mean age of the 43 men was 58.3 years (s.d. 10.435) and ranged from 35 to 75 years.

The men were randomised to receive the MIDUS or three nights RigiScan first. In all, 19 of the 43 (44%) underwent the three night nocturnal RigiScan monitoring prior to the ultrasound assessment.

RigiScan nocturnal assessment

Table 1 shows the average maximum penile base and tip rigidity and tumescence over the three night nocturnal RigiScan monitoring. Overall, 42/43 (98%: 95% CI: 88–100%) of the men experienced some event, on at least one occasion over the three nights, although for only 38/43 (88%, 95% CI: 76–95%) of the men did these events exceed 3 min.

Table 1 RigiScan night time assessment results (over three nights) (n=43)

Table 2 shows the average RAU and TAU base and tip scores over the three night nocturnal RigiScan monitoring.

Table 2 RAU and TAU results from RigiScan night time assessment (over three nights) (n=43)

Table 3 shows the results of the MIDUS assessment for the 43 men. In all, 17 out of 43 (40%, 95% CI: 26–54%) of men had a normal end-diastolic flow velocity (EDV)6, 7, 8 of less than 4.5 cm/s, whereas 32/43 (74%, CI: 60–85%) had a normal PSV8, 9 greater than 35 cm/s.

Table 3 Results from ultrasound assessment

RigiScan vs MIDUS

Tables 4 and 5 show the results of the paired comparisons between the nocturnal RigiScan and the MIDUS assessments. For example, 38/43 (88%) of the men experienced an event of over 3 min duration on the nocturnal RigiScan, compared to 17/43 (40%) having a normal EDV of less than 4.5 cm/s on the ultrasound (excluding veno-occlusive disorder) (Table 4), giving a difference of 48% (95% CI: 31–62%). These event rates were significantly different (P<0.017).

Table 4 Presence of normal responses on ultrasound (i.e. EDV<4.5 cm/s) and RigiScan events (any events >3 min, over three nights)
Table 5 Presence of normal responses on ultrasound (i.e. PSV >35 cm/s) and RigiScan events (any events >3 min, over three nights)

Likewise, 38/43 (88%) men experienced an event of over 3 min duration on the nocturnal RigiScan compared to 32/43 (75%) having a normal PSV (>35 cm/s) on the ultrasound (Table 5), giving a difference of 13% (95% CI: −3 to 30%). These event rates were not significantly different (P=0.18).

During the MIDUS assessment the researchers took the most extreme response from either artery to determine the PSV or EDV values.


In all, 38/43 (88%, 95% CI: 76–95%) of men had a nocturnal event exceeding 3 min on the RigiScan investigation. This compares with 17/43 (40%, 95% CI: 26–54%) of men with a normal EDV blood flow of less than 4.5 cm/s (P<0.017) and 32/43 (74%, CI: 60–85%) of men with a normal PSV flow greater than 35 cm/s (NS). In terms of confirmation of a diagnosis the results suggest there is no significant difference between RigiScan and MIDUS, when looking at the PSV measurement. However, there are significant differences in terms of diagnosis between the methods when using the EDV measurement.

There are certain advantages to each procedure that warrant consideration. For example, the RigiScan uses standardised measures of rigidity which are repeatable between subjects. MIDUS has the benefit of immediate positive audible and visual feedback allowing the clinician the ability to augment the investigation with additional stimulants (audiovisual, vibratory, intracavernosal) as required. However, as with the RigiScan, MIDUS is invasive and has an immediate effect on patient privacy. Additionally, as with the DDU, MIDUS is skills dependent.

The MIDUS does allow visual and audible inspection of normal vasculature that can be reassuring to patients. Despite the suggestive history and the ambivalent PRS results, many men in the study had a positive PSV on MIDUS and NPTR. So where arterial pathology is evident, either test will be beneficial.

Where there is marked veno-occlusive disorder, there are significant differences in the diagnostic usefulness of the two methods. It is much less the case that use of the RigiScan measures will be sufficient to diagnose this scenario (and visual observation of the recording is inexact). In these circumstances the use of MIDUS or DDU is recommended. While there remains the possibility that false positive results have been observed, a second dose of vasoactive agent was injected using current established criteria for making such a diagnosis.

The aim of this study was to evaluate the effectiveness of MIDUS in its portable state as compared to NPTR using RigiScan. In the patients we studied, that had a suspected vascular aetiology to their ED, we have shown that there is no statistical difference in the results gained from either methodology using the PSV measurement. Both allow for the accurate confirmation of what remains a diagnosis rooted in sound clinical assessment, experience and knowledge. However, those men with veno-occlusive disorder require the diagnosis to be confirmed using MIDUS/DDU. In cases of marked anxiety and psychological contributory factors, RigiScan and ultrasonography can play a considerable role in giving the male suffering from ED a much needed quantitative, visible test that can go some way toward releasing the sufferer from what might have been months, even years of doubt about their own sexual viability thus allowing rational treatment to commence.

Our conclusion is that when comparing RigiScan with MIDUS, the actual diagnostic efficacy for arterial disease is equivalent and so either test is valid. However, where there is veno-occlusive disorder, the NPTR is less specific and where possible we suggest from our findings that the first line investigation should be ultrasonography/MIDUS. Where arterial reconstruction is necessary, the recordings from DDU (not MIDUS) are required which makes it the absolute gold standard in testing of this nature. At present RigiScan should remain first line investigation in suspected neurological and psychological ED if investigation is deemed valuable as part of the overall assessment as it can be used while the patient is asleep.


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Correspondence to K R Wylie.

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Wylie, K., Davies-South, D., Steward, D. et al. A comparison between portable ultrasound (MIDUS) and nocturnal RigiScan when confirming the diagnosis of vascular organic erectile disorder. Int J Impot Res 18, 354–358 (2006).

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  • erection
  • RigiScan
  • vascular dysfunction
  • ultrasound


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