Functional ultrasound imaging of the venous valve of the great saphenous vein in the area around the crosse using the novel vector flow technique

Abstract

PURPOSE:

The aim of our pilot study is to consider if the new flow presentation of the vector flow (V-flow) allows an assessment of the valve morphology of the crosses with respect to an insufficiency.

MATERIAL AND METHODS:

We performed a total of 50 investigations in which we documented a complete valve closure at the so called “crosse” at the valve of the large saphenous vein, a delayed valve closure or an incomplete valve closure with consecutive insufficiency at the crosse. The valve function of the crosse is crucial for the development of varicosis. For our study we recorded age and gender of the patients. One patient in the study was suffering from Covid19. For the examinations we used a 3–9 MHz probe and a high-end ultrasound device. The examination was performed in a lying position and under quiet conditions. Before examination we practiced inhalation and exhalation as well as “pressing” or coughing with the patients, which resulted in a physiological closure of the venous valves. To rule out thrombosis, we carried out compression sonography on the legs. During the examination we documented the B-scan, the Color-Coded Duplex Sonography, the HR-flow and the V-flow for 3 seconds at the estuary of the crosses and incorporated these parameters into our measurements. Via V-flow, vectors can be imaged by representing the flow of erythrocytes and visually indicate a possible insufficiency due to delayed or incomplete valve closure.

RESULTS:

31 of 50 patients (age 19–81years) showed a complete valve closure of the crosses, three of them suffered from thrombosis. In eight of the 50 study participants (age 45–79 years) a delayed valve closure could be diagnosed by V-flow within 1–2 seconds. None of them had a thrombosis, but six of them suffered from cancer. In eleven patients we derived an incomplete valve closure with insufficiency (age 51–88 years). With reflux it took >2 seconds to close the valve. The patient with Covid19 also showed an incomplete valve closure with insufficiency. At the same time this patient showed a Covid19-associated deep vein thrombosis. Eight additional patients also had a thrombosis. Six of them suffered from cancer. Overall, the results were best visualized by V-Flow.

CONCLUSION:

The crosse as a significant venous structure can be well investigated by V-flow with respect to hemodynamic changes and a resulted reflux. Also associated changes close to the valve can be visualized well.

Keywords

Valve insufficiency crosses CCDS (color-coded duplex sonography)V-flow

1 Introduction

Chronic venous insufficiency is based on a change in the number and function of venous valves. This is often the result of varicosis which affects women in particular [1]. With increasing age and also after thrombosis or thrombophlebitis, the number of venous valves decreases significantly. As a consequence, hyperpigmentation, edema, venous eczema, atrophy blanche and ulcers occur [2]. The early detection of a truncal varicosis depends on the examination of the venous valve function in the area of the so-called “crosse”, a segment of the saphenofemoral junction [3]. It is located at the confluence of the great saphenous vein into the femoral vein below the inguinal ligament.

In recent years, ultrasound diagnostics using B-scan and Color-Coded Duplex Sonography (CCDS) have become increasingly established to assess morphological and functional vein changes [4]. For thrombosis diagnostics, high-resolution sonography is now regarded as the diagnostic method par excellence [5, 6]. When assessing venous valve function, the difficulty for CCDS is duplex imaging. This results in angle-dependent flow imaging and difficulties in imaging very low and very high flows simultaneously without artifacts.

This would require digital dynamic flow methods. X-ray imaging targeted at transmission, as in phlebography, is associated with a not inconsiderable radiation exposure [4, 10].

Studies on the so-called B-flow have already been carried out on the development of digital flow processes [8]. Here, several pulses are synchronized according to a digital subtraction, so that moving spreaders can be amplified and stationary tissue can be subtracted. This offers advantages to avoid Doppler artifacts such as aliasing or vessel oversubscription, vibration artifacts or blooming [7]. The advantage of this application is that it can visualize hemodynamic flow respecting stationary tissue and changes in the vascular anatomy in real-time [7, 8]. Depending on the manufacturer, these digital flow methods have further established themselves in everyday clinical practice with designations such as “fine-flow”, HR-flow and S-flow [4 , 7–9].

In the case of vector flow, care was taken to ensure that the hemodynamics are additionally represented by different numbers, lengths and color coding of flow vectors, since, especially in intact venous valves, there are very differentiated flow changes in the Valsalva experiment with resting flow, accelerated flow, flow reversal and flow stop. It is advisable, in correlation with Color-Coded Duplex Sonography (CCDS), to check at the estuary of the valve of the great saphenous vein, the crosse, which changes can clearly be represented with V-flow. So far, there are first experiences with the model of arterial flow with significantly higher flow velocities [9].

The aim of our pilot study was to record vector flow for the first time in the dynamics of the Valsalva press test on the venous crosse for valve function diagnostics using the new V-flow technique.

2 Material and methods

The evaluation is retrospective based on digitally stored image sequences. The study was approved by the local ethics committee (approval number 20-1909-104).

All examinations were carried out with the consent of the patients to be examined on the basis of clinical questions regarding a possible venous insufficiency or for the exclusion of deep vein thrombosis in daily clinical practice. As a standard procedure, compression sonography was used to exclude thrombosis on both legs in accordance with DEGUM guidelines [10]. A linear transducer probe (3–9 MHz) was used for this purpose. The valve function of the crosses was performed in modified, obliquely angulated sections without compression.

The most frequent pathophysiological mechanism of chronic venous diseases is venous reflux. This can be easily visualized by Color-Coded Duplex Sonography (CCDS). With V-flow, however, the reflux and the associated turbulence at the area around the valve of the great saphenous vein into the femoral vein can be depicted even more clearly. With the help of the Valsalva maneuver a reflux can be provoked. The background is that the antegrade pressure is increased accordingly by the Valsalva press test. An incomplete valve closure at the crosse is characterised by the occurrence of reflux and turbulence [11]. Using V-flow, reflux is shown by a flow reversal of the vectors to retrograde, the vectors show a color change from green to red and, in the case of turbulent flows, the vectors run undirected.

Deep inspiration and expiration measurements were performed with the CCDS and the valve was closed as completely as possible by compression testing. The aim was to achieve a flow stop after half a second as a rule. Valve closure was prolonged after 1–2 seconds and pathologically after more than 2 seconds. The color coding and Doppler spectrum was always documented under flow-adapted parameters of pulse repetition frequence (PRF), Doppler and color gain and wall filter. All investigations were performed by an experienced investigator.

Based on clinically induced ultrasound examinations, which included the groin region, a supplementary vector flow measurement was carried out in the area of the crosses under Valsalva experiment in addition to the diagnostic examinations. Initially, thrombosis was ruled out by means of B-scan sonography in the compression test. Using CCDS, flow documentation was carried out in inhalation, exhalation and compression test, Valsalva in the area of the crosses.

The normal valve function was assessed as inspiratory and expiratory breath modulation with flow velocities between 5–35 cm/s. A spontaneous interruption of venous flow or a zero flow in a maximum of half a second was evaluated as normal valve closure in the Valsalva press test. Delayed valve closure was evaluated with the CCDS after 1–2 seconds in the case of prolonged color change and flow stop. A complete valve failure was found in the case of sustained flow during the pressing test, spectrally below the zero line with significant reflux. Hemodynamic flow parameters were set to low flow for normal venous flow, PRF max. 100 Hz and flow velocity between 5–35 cm/s. In the Valsalva press test, the flow rate was adjusted to max. 100 cm/s.

The vector flow was measured with a 3–9 MHz probe in linear matrix technique. The mean flow velocity was adjusted to 25 cm/s. Since a tilting of the sound window was not possible at present, the crosse was sonicated at an angle of 30–60 degrees.

The maximum window width was adjusted to the muzzle flap area. The line density and frame rate were set to medium ranges. A spontaneous interruption of the blood flow was evaluated as normal valve function when a zero flow was reached. The maximum image recording time was 3 seconds. In the Valsalva press test, a reversal of the vector functions with reaching zero flow within the 3 seconds period was evaluated as valve restriction. A change of vector length, reversal of vector direction and change of vector density lasting from the press test of the flap damage was evaluated. This was correlated with the results of the Doppler function test of the CCDS.

3 Results

Overall, 50 patients were included in our retrospective study, thereof 28 male and 22 female participants aged 19 to 88 years.

The following Table 1 shows a classification of patients according to gender, age, the presence of a thrombosis or/and a malignant disease, the presence of coronavirus disease 2019 and a proper, delayed or insufficient valve closure in the Valsalva maneuver.

Table 1
Classification of patients according to gender, age, the presence of a thrombosis or/and a malignant disease, the presence of coronavirus disease 2019 and a proper, delayed or insufficient valve closure in the Valsalva press test

Male Female Age Thrombosis Cancer Coronavirus disease 2019 Proper Valsalva press test Delayed Valsalva press test Insufficient Valsalva press test

1 x 66 x x

2 x 61 x x

3 x 65 x x

4 x 78 x x

5 x 73 x

6 x 76 x

7 x 70 x

8 x 79 x

9 x 40 x x

10 x 66 x x

11 x 77 x x

12 x 24 x

13 x 55 x

14 x 40 x x

15 x 45 x

16 x 54 x x

17 x 66 x x

18 x 77 x x

19 x 53 x x

20 x 78 x x

21 x 25 x

22 x 65 x x x

23 x 77 x x

24 x 67 x x x

25 x 51 x x

26 x 20 x x

27 x 68 x x

28 x 56 x

29 x 26 x

30 x 35 x

31 x 21 x

32 x 67 x x x

33 x 81 x

34 x 71 x x x

35 x 88 x x

36 x 19 x

37 x 56 x x

38 x 52 x x

39 x 47 x

40 x 63 x x

41 x 57 x x

42 x 53 x x

43 x 60 x

44 x 48 x

45 x 51 x x

46 x 53 x x x

47 x 52 x x

48 x 54 x x x

49 x 56 x x x

50 x 54 x

Total 28 22 12 26 31 8 11

	Male	Female	Age	Thrombosis	Cancer	Coronavirus disease 2019	Proper Valsalva press test	Delayed Valsalva press test	Insufficient Valsalva press test
1	x		66		x		x
2		x	61		x		x
3		x	65		x				x
4		x	78	x			x
5	x		73				x
6	x		76				x
7	x		70				x
8		x	79					x
9		x	40		x		x
10	x		66		x		x
11	x		77		x		x
12		x	24				x
13		x	55				x
14	x		40		x		x
15	x		45					x
16		x	54	x		x
17	x		66		x		x
18	x		77		x			x
19	x		53		x		x
20	x		78		x		x
21		x	25				x
22	x		65	x		x			x
23		x	77		x		x
24	x		67	x	x				x
25		x	51		x		x
26		x	20		x		x
27	x		68		x			x
28		x	56				x
29		x	26				x
30	x		35				x
31		x	21				x
32	x		67	x	x				x
33		x	81				x
34		x	71	x	x		x
35		x	88	x					x
36	x		19				x
37		x	56		x			x
38	x		52		x			x
39		x	47				x
40	x		63	x					x
41	x		57		x			x
42	x		53		x			x
43	x		60						x
44	x		48				x
45	x		51	x					x
46	x		53	x	x				x
47		x	52	x			x
48	x		54	x	x				x
49		x	56	x	x				x
50	x		54				x
Total	28	22		12	26		31	8	11

None of our 50 study participants underwent surgery for varicosis.

3.1 Complete valve closure

In the Valsalva press test 31 patients (age 19–81years) showed a complete closure of the valve of the crosses within half a second. Among them there were 14 male and 17 female, three of them had thrombosis. 14 of them were affected by cancer including one patient with a thrombosis.

Antegrade directional vectors (green colored) could be mapped in the V-flow. There is no occurrence of undirected vectors (yellow colored) or turbulence (red colored vectors). The following Fig. 1a–c show a regular valve closure in the V-flow.

Fig. 1

a. Antegrade, directed flow of short vectors at the estuary of the valve from the great saphenous vein into the femoral vein. b. Within half a second, the Valsalva press test causes the valve to close completely in the area of the crosses. The consequence is a zero blood flow. Therefore, no vectors can be depicted here. c. After completion of the Valsalva press test, the valve opens, allowing blood to flow through the estuary of the valve again. Antegrade, directed, short vectors (green colored) are derived.

3.2 Delayed valve closure

In eight of the 50 study participants (age 45–79 years) a delayed valve closure could be diagnosed by V-flow. Two of them were female, six male. None of them had a thrombosis, but six of them suffered from cancer.

During the Valsalva press test there was a delayed valve closure after 1–2 seconds. Most of the vectors are antegrad and directional (green colored), but some non-directional vectors (yellow colored) can also be derived. The following Fig. 2a–d show a delayed valve closure in the V-flow.

Fig. 2

a. Most vectors show an antegrade, directed flow (green colored) at the estuary of the valve from the great saphenous vein into the femoral vein. But some of them are non-directed (yellow colored). b. When asked to perform the Valsalva press test, there is a delay in valve closure of 1–2 seconds. Some vectors must still be derived until valve closure is complete. c. After 1–2 seconds a complete closure of the valve at the crosse can be seen. The blood flow stops. No vectors can be derived. d. After completion of the Valsalva press test, the valve opens. Now blood can flow again through the estuary of the valve. For the most part antegrade, directed vectors (green colored) can be derived. A small proportion of the vectors are non-directed (yellow colored).

3.3 Incomplete valve closure

In eleven patients we derived an incomplete valve closure (age 51–88 years) with consecutive insufficiency. Three of them were females and eight males. Among them one patient showed a coronavirus disease 2019 associated deep vein thrombosis. It is now known that coronavirus disease 2019 is associated with deep vein thrombosis of the leg and subsequent pulmonary embolism [13, 14]. Eight additional patients also had a thrombosis. Six of them suffered from cancer.

An incomplete valve closure results in an insufficiency. Even during the Valsalva press test, blood passes through the valve estuary. Since the valve is not completely closed, a venous reflux with retrograde flow occurs, i.e. against the physiological flow direction. The flow reversal is measured distal to the valve. In addition, turbulence is created, which is illustrated by the V-flow through a disordered alignment of the vectors and a color change from green (antegrade flow) to red (turbulent flow). The blood, which continues to pass through the deficient valve, also shows a turbulent flow with non-directed (red) vectors. The following Fig. 3a–d show an insufficient valve closure in the V-flow in a patient suffering from thrombosis.

Fig. 3

a. If there is an insufficiency at the valve level, non-directional vectors with an increased blood flow velocity can be displayed in V-flow (red colored). b. Even after 1–2 seconds after the request to perform the Valsalva press test, there is no adequate valve closure. Blood passes through the incompletely closed valve, which rushes through the valve estuary. A retrograde blood flow occurs, which is called “reflux”. This leads to an increase of the hydrostatic pressure. The consequence is an increased blood flow rate (extended vectors) with undirected, extended vectors (red colored). c. If the valve is not closed completely during Valsalva press test in the area of the crosses, turbulences of the blood flow will appear a few seconds after fully opening the valve. These can be represented by non-directional vectors (red colored). In addition, an increased blood flow rate is also shown by an increased blood flow velocity. This is represented by an extension of the vectors. d. After completion of the Valsalva press test, the venous valve opens to its original diameter. However, turbulence still occurs, as can be seen from the non-directional, elongated red vectors.

4 Discussion

The V-flow makes it possible to clearly show morphological and hemodynamic changes, as they are presented in the Valsalva experiment as a functional model of a venous valve alteration. Thereby, changes during inhalation, exhalation and under Valsalva pressure on the estuary of the valve can be shown very precisely through the vector size, number, different color coding, direction, length and different density of the vectors. The results of our first evaluation indicate that the V-flow has a great diagnostic potential to detect functional changes at the venous valve level. It is possible to differentiate between normal valve flow, between incipient valve insufficiency and complete valve insufficiency. Under difficult examination conditions with CCDS, this may, in some cases, only be possible to a limited extent [10].

The results of the present pilot study underline the importance of modern ultrasound diagnostics including newly developed digital flow methods with vector imaging for the morphological and functional assessment of venous flow. At the crosse, where Valsalva experiments lead to a combination of low flow to be detected, very high flow due to pressing and, ideally, zero flow, the vector flow can vividly illustrate these changes by imaging a changed vector density and direction and leads to a change of color-coded vector with increasing vector length. CCDS has already established itself as a reliable functional imaging method in comparison to phlebography [5]. Nevertheless, CCDS is limited by the Doppler principle and requires appropriate examination experience for optimal venous valve assessment. The flow parameters, especially the PRF, the wall filter, the gain, the measurement volume and the color box must be optimally adjusted in order to assess regular, impaired or pathological valve function. The optimal angle of incidence is also particularly important. A further limiting factor in color coding is that movement artefacts, vascular exaggeration and possible aliasing have a limiting effect on the Valsalva press test [10, 11].

Here, due to the fact of digital flow recording, a detailed, almost artifact-free flow detection close to the valve can be achieved with the V-Flow. Thus, our first study results open further investigations for functional flow changes with the V-Flow [9].

Limitations of the V-Flow currently are that the technology can only be used with a high-end ultrasound device, which is not available everywhere, and a linear probe in the range of 3–9 MHz. Technical limitations are that the color box measures max. 3 cm and cannot be tilted. Furthermore, it is only possible to penetrate to a depth of 5 cm. Currently, the flow cannot be regulated lower than approximately 20 cm/s which still limits the use of the technique in the peripheral area. The maximum recording time is 3 seconds.

At present, according to other studies, the focus is still on the high flow range in the arterial flow basin. Qiu et al. already investigated high-frequency areas such as the carotids with the help of V-flow [9]. We now carried out investigations of the low-frequency areas in the venous system at the area around the great saphenous vein. However, these results support the current study in this respect. The latest current publications on venous ultrasound diagnostics mainly include thrombosis diagnostics, fistulas and malformations. All these may be a possible basis for a new study.

4.1 Conclusion

With the help of V-flow, the flow representations in the vessels can be carried out simply, quickly and also easily. Hemodynamic changes and a resulting reflux can be clearly illustrated. Even changes close to the valve can be visualized well with V-flow. The V-flow is an important tool for assessing changes in the venous system and evaluating valve function.

Conflict of interest

The authors have no conflict of interest to report.

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