14 Applications of Ultrasound Microbubbles in the Spleen

14 Applications of Ultrasound Microbubbles in the Spleen

Christopher J. Harvey, Adrian K.P. Lim, Madeleine Lynch, Martin J.K. Blomley, David O. Cosgrove

C. J. Harvey, MRCP FRCR, Consultant Radiologist A. K. P. Lim, MRCP FRCR, Consultant Radiologist M. Lynch, MSc, Senior Sonographer

M. J. K. Blomley, MD, FRCR, Professor of Radiology D. O. Cosgrove, FRCP FRCR, Professor of Clinical Ultrasound Department of Imaging, Imaging Sciences Department, Ham- mersmith Hospital, Imperial College Faculty of Medicine, 150 Du Cane Road, W12 OH5, London, UK

hepatosplenic-specific uptake after their disappear- ance from the blood pool phase (Blomley et al. 1999;

Forsberg et al. 1999). They are Levovist, Sonavist (both Schering AG, Germany) (Blomley et al. 1999;

Forsberg et al. 1999) and Sonazoid (NC100100;

Nycomed Amersham, Norway) (Leen et al. 1998), of which only Levovist remains in clinical use. The site of accumulation within these organs is unknown but is thought to be the reticuloendothelial system or sinusoids (Leen et al. 1998; Blomley et al. 1999;

Forsberg et al. 1999; Kono et al. 2002). However, there is relatively few published data with regard to microbubbles and their behaviour in the spleen.

The most widely used microbubble in Europe, Sono- Vue (Bracco, Italy), had always been thought to be a purely vascular contrast agent (Schneider et al.

1995; Correas et al. 2001; Harvey et al. 2001).

We investigated the enhancement characteris- tics of SonoVue in the normal spleen in a cohort of ten healthy volunteers. Using a low acoustic power technique [Cadence Contrast Pulse Sequence (CPS), Sequoia, Acuson-Siemens, USA], the spleen was con- tinuously scanned from 0 to 60 s and then again at 4 min. SonoVue (2.4 ml) was injected intravenously in all volunteers. Early analysis of this unpublished data revealed that in nine out of ten volunteers, there was heterogeneous, patchy enhancement of the spleen from 0 to 20 s (Fig. 14.1), with the spleen then becoming homogeneous throughout by 50 s (Fig. 14.2a). In one volunteer the spleen homogene- ously enhanced even in the arterial phase. These enhancement characteristics are similar to those reported with iodinated contrast agents within the spleen on computed tomography (CT) and mag- netic resonance (MR) imaging (Glazer et al. 1981;

Mirowitz et al. 1991). These imaging characteristics are thought to be due to variable flow rates through the cords and sinuses of the red pulp (Groom 1987).

Therefore it is recommended that lesion detection and assessment of the spleen with microbubbles should be in the late phase, at least 60 s post intra- venous injection. The images at 4 min revealed that there was still a significant amount of contrast

14.1 Introduction 205

14.2 Microbubble Behaviour in the Normal Spleen 205 14.3 Splenic Lesions 207

14.3.1 Congenital Lesions 207

14.3.2 Benign Focal Splenic Lesions 208 14.3.3 Malignant Focal Splenic Lesions 212

14.3.4 Splenic Renal Perfusion Defects - Infarctions 216 14.3.5 Splenic Abscesses 216

14.3.6 Heterogeneous Splenic Echotexture 216 14.4 Summary 216

References 218

14.1

Introduction

Ultrasound (US) is a reliable method of demonstrat- ing and estimating the size of focal splenic abnor- malities with the added benefits that there is no risk of ionizing radiation and that it is quick and easy to perform. It is only relatively recently, since the advent of microbubble contrast agents, that US has been able to investigate splenic enhancement patterns and characterize focal lesions. This chapter describes the applications of US microbubbles in the identifica- tion and characterization of focal splenic lesions.

14.2

Microbubble Behaviour in the Normal Spleen

Microbubbles were initially thought to be purely

vascular agents. However, three agents demonstrate

agent in the splenic tissue after the normal vascular phase (Fig. 14.2b), suggesting that SonoVue also has splenic specificity.

An expanded study of these normal volunteers con- firmed the splenic tropism of SonoVue at least 5 min after the blood pool phase (Lim et al. 2004). Figure 14.3 demonstrates a series of images of the spleen from 0 to 5 min after contrast injection in the same volunteer.

The green pixels depict stationary microbubbles using low acoustic power software [Vascular Recognition Imaging (VRI), Aplio, Toshiba, Tokyo, Japan]. Note that the intensity of the green pixels remains relatively

unchanged over the 5 min. The percentage of green pixels in a region of interest was used for quantifica- tion, and Fig. 14.4 is a graph illustrating the mean quantity of microbubbles within each organ (i.e. liver, spleen and both kidneys) over 5 min in the 20 normal volunteers. These data confirmed specific uptake of SonoVue by the spleen but not the liver.

It is interesting that, of the aforementioned agents, SonoVue demonstrated only splenic-specific uptake- without significant liver tropism. Thus the exact mech- anism of microbubble uptake in the spleen, which has previously been attributed to phagocytosis by macro- phages (this also applies to liver uptake), remains ques- tionable. The behaviour of SonoVue may be analogous to that of the heat-damaged red blood cells used in nuclear medicine, which are highly spleen-specific and are not taken up by the liver, unlike colloid-labelled trac- ers (Massey and Stevens 1991; Person and Bender 2000). Phase contrast microscopic studies by Iijima et al. (2003) with in vitro hepatic macrophages suggested that these cells were selective for microbubble agents that were phagocytosed and that this process was pos- sibly dependent on the structure of the agent.

Though the exact physiology and kinetics of these microbubble agents in the spleen may be unknown, this unique spleen specificity provides a useful alter- native method for identifying or confirming splenic tissue, as well as for characterizing focal splenic lesions with an accuracy that rivals that of CT, MR imaging, or nuclear medicine imaging.

Contrast-specific techniques operating at low acous- tic power [mechanical index (MI) <0.2 and sometimes as low as 0.02] present the major advantage that tissue harmonics are suppressed, and that bubble destruc- tion is minimised. These technological advances com-

mode (Cadence Contrast Pulse Sequencing, CPS, Sequoia, Acuson-Siemens, USA), which depicts microbubbles in a colour overlay. This is an example of the heterogeneous enhancement of the spleen in the arterial phase. Note the apparent rounded defect, which could be mistaken for a lesion (arrow).

a b

Fig. 14.2. a The spleen in the same volunteer as in Fig. 14.1 now dem- onstrates homogeneous enhancement at 60 s.

The apparent defect in Fig. 14.1 is not visible now. b At 4 min there is still microbubble agent within the spleen.

Fig. 14.3a–c. The images are of the same volunteer as in Figs. 14.1 and 14.2, at baseline (a), 3 min after contrast injec- tion (b) and 5 min after contrast injection (c). In this mode, stationary microbubbles are depicted in a green colour (Vas- cular Recognition Imaging, Aplio, Toshiba, Japan).

a b

c

Fig. 14.4 A graph illustrating the mean total microbubble uptake against time (s) in a cohort of 20 volunteers over 5 min.

Gradients of best-fi t straight lines have been plotted. Note that the line for the spleen is virtually horizontal, while the other organs demonstrate decreases at a similar rate. The elevated values for the liver compared with the kidneys were thought to be due to the larger vascular volume of the liver.

bined with the availability of more stable microbub- bles (e.g. SonoVue) have facilitated the development of real-time non-destructive (MI 0.06–0.12) imaging modes that can demonstrate the capillary bed as well as larger vessels (Harvey and Albrecht 2001). Con-

trast-enhanced imaging of focal splenic lesions may be divided into arterial (20-25 s) and portal (45–90 s) phases and sinusoidal (>90 s). Real-time imaging allows these phases to be followed successively so that the dynamic enhancement pattern and vascular morphology may be assessed. The low acoustic power means that continuous imaging can be performed for as long as the agent persists (5–10 min after a full dose of SonoVue). This technique has replaced the destruc- tive high acoustic power approaches.

14.3

Splenic Lesions

14.3.1

Congenital Lesions

A splenunculus is accessory splenic tissue which is present in 10–30% of the population (Gorg 2001;

Peddu et al. 2004). Splenunculi may be single or mul-

tiple and most commonly occur at the splenic hilum

(75%) (Wadham et al. 1981). They typically have a

round contour and their echogenicity is identical to

that of the parent spleen. Any pathological process

affecting the spleen may affect the splenunculus.

Splenunculi have a vascular hilum with an arterial and venous supply running in opposite directions (Bertolotto et al. 1998). Splenunculi have identi- cal enhancement patterns, with US microbubbles, to the adjacent spleen. Splenunculi and the parent spleen enhance simultaneously in the arterial phase and exhibit a heterogeneous sinusoidal phase. As described above, some agents (Levovist, SonoVue) have a delayed splenic-specific parenchymal phase which is useful in differentiating splenunculi from lymph nodes or pancreatic masses (Figs. 14.5, 14.6).

14.3.2

Benign Focal Splenic Lesions Cystic Lesions

Cystic splenic lesions may be subdivided into primary cysts, which are either non-parasitic (epithelial) or parasitic (echinococcosis infection), and secondary cysts, which are thought to be traumatic in aetiol- ogy (Dachman et al. 1986; Siniluoto et al. 1994;

Urrutia et al. 1996). They contain blood and debris and may exhibit mural calcification.

Fig. 14.5a, b. A 56-year-old patient with a past history of pancreatic gastrinoma. a Baseline US revealed a mass (arrow) at the splenic hilum and a tumour recurrence was queried. Note that the lesion has a smooth contour and shows the same echogenicity as the spleen. b Three minutes after an IV bolus injection of 2 g Levovist, using the stimulated acoustic emission (SAE) mode, similar colour phenomena are revealed in the spleen and adjacent lesion, confi rming this to be a splenunculus (arrow). Note the marked focal zone dependence of this mode as the highest acoustic power occurs at this position.

a b

Fig. 14.6a,b. Enlarged accessory spleen in a patient who had undergone splenectomy 5 years previously. Baseline US (a) reveals a tumour-like round lesion (arrow) at the splenic site. The splenic-specifi c concentration of sulphur hexafl uoride-fi lled micro- bubbles 4 min after injection (b) proves the splenic nature of the lesion. (From the editor, E. Quaia).

a b

Non-parasitic cysts show the classic US features of anechoic contents, with posterior acoustic enhance- ment and smooth walls. They are avascular on Doppler imaging (Gorg and Schwerk 1994; Gorg et al. 1991).

Microbubble contrast agents may be helpful in defining the thin wall of the cyst and demonstrating the absence of central enhancement to differentiate benign simple cysts (Fig. 14.7) from infective or neo- plastic cystic lesions.

Hydatid cysts are rare in the spleen (less than 5%

of Echinococcus infections). They may be anechoic or have heterogeneous echogenicity due to scolices (Beggs 1985; Polat et al. 2003). The ‘water-lily sign’

is characteristic of the condition and is caused by separation of the membranes of the cyst. With IV microbubbles, hydatid cysts show peripheral but not internal enhancement.

Haemangiomas

Haemangiomas are the commonest benign primary splenic neoplasm, with a prevalence of 0.3–14%

at autopsy (Ros et al. 1987; Ramani et al. 1997).

They are tumours of the epithelium of the vascular sinuses and are more commonly cavernous than capillary in pattern. Cavernous haemangiomas are usually small (<2 cm) and are incidental findings on imaging. They are slow growing. Occasionally haemangiomas may be large and may present as a mass or with rupture and bleeding (Husni 1961).

Multiple splenic haemangiomas occur in Klippel-

Trenaunay syndrome and may be complicated by rupture, hypersplenism and malignant change.

On US, haemangiomas typically appear as well- defined avascular echogenic lesions (Ros et al. 1987;

Urrutia et al. 1996; Wan et al. 2000). Atypical fea- tures, which are more commonly present in large cavernous haemangiomas, include cystic change and calcification.

Small haemangiomas uniformly enhance with microbubbles (Fig. 14.8), whereas larger lesions exhibit centripetal filling in on delayed imaging (Fig. 14.9).

However, larger lesions with cystic/necrotic/throm- botic components may show heterogeneous enhance- ment (Fig. 14.10) rather than the centripetal pattern (Abbott et al. 2004). This is due to the fact that cystic spaces (often central) do not possess blood-filled vascular spaces. Also, splenic haemangiomas do not exhibit the well-defined peripheral globular coalesc- ing enhancement pattern seen in hepatic haeman- giomas (Urrutia et al. 1996; Ramani et al. 1997;

Abbott et al. 2004). This may be due to differences in vascular supply such that peripheral nodules (present in liver haemangiomas on contrast-enhanced US, CT and MR) are less conspicuous in splenic haemangi- omas in the arterial phase because splenic enhance- ment obscures them (Ferrozzi et al. 1996).

Hamartomas

Splenic hamartomas, also known as splenomas, splenadenomas and nodular hyperplasia of the

Fig. 14.7a,b. A 40-year-old man who presented with left upper quadrant pain. a Baseline US showed a well-defi ned, predomi- nantly echo-poor splenic lesion with mobile debris within it, consistent with a complex cyst. b Imaging in the late splenic- specifi c phase of Levovist using the phase inversion mode (ATL-Philips, USA) showed no microbubble activity in the cyst but demonstrated normal uptake in the adjacent spleen, rendering the cyst more conspicuous. The fi nal diagnosis was thought to be haemorrhage into a simple epithelial cyst as there was no evidence of sepsis.

a b

Fig. 14.8a–c. Small splenic haemangioma. The lesion (arrow) appears hypervascular with peripheral and central vessels on Power Doppler US (a). Diffuse and persistently homogeneous enhancement is evident (arrow) at phase inversion more (ATL- Philips, USA) both 25 s (b) and 2 min (c) after microbubble injection. (From the editor, E. Quaia).

a b c

Fig. 14.9a–f. Splenic haemangioma. a B-mode ultrasound showing a focal echo-poor splenic lesion (arrow) which was an inci- dental fi nding. b No colour Doppler signal was present in the lesion (arrow). c Imaging in the late splenic-specifi c phase of Levovist using the phase inversion mode (ATL-Philips, USA) shows partial centripetal fi lling-in of the lesion (arrow) at 3 min post injection. d Imaging using the stimulated acoustic emission (SAE) mode also exhibits fi lling-in (arrow) at 3 min post injection. e Arterial phase CT shows intense peripheral enhancement (arrow). f Delayed phase CT (5 min post contrast) shows that the lesion (arrow) has completely fi lled in. The appearances are consistent with a haemangioma although the echo-poor appearance on B-mode ultrasound is atypical.

a b c

d

e f

spleen, are rare benign tumours occurring with an incidence of 0.024–0.13% in autopsies (Silverman and Livoisi 1978). Splenic hamartomas are usu- ally found incidentally, although rupture has been described (Ferguson et al. 1993).

On US, splenic hamartomas are usually solid homogeneous masses and hyperechoic relative to the adjacent splenic parenchyma (Gorg and Schwerk 1994; Ferguson et al. 1993; Ramani et al. 1997;

Wan et al. 2000). However, some may be heteroge- neous, with cystic changes and areas of calcification secondary to ischaemia or haemorrhage. They are usually hypervascular on colour Doppler (Tang et al. 2000) (Fig. 14.11). This is thought to reflect the hypervascularity of the red pulp in the hamartoma.

Variable enhancement is seen following intravenous microbubble injection.

Lymphangioma

Splenic lymphangioma is a rare slow-growing benign tumour. It is characterized by splenic cysts of varying sizes from a few millimetres to several centimetres (Komatsuda et al. 1999). Splenic lymphangiomas may occur in isolation or with multisystem organ involvement (Rao et al. 1981; Morgenstern et al.

1992; Wadsworth et al. 1997; Komatsuda et al.

1999). Complications are associated with the more extensive or larger lymphangiomas and include bleed- ing, hypersplenism, consumptive coagulopathy and portal hypertension. Malignant transformation has been described in one case (Feigenberg et al. 1983).

On US, splenic lymphangiomas appear as cystic lesions with septation, echogenic debris and calci- fication (Fig. 14. 12) (Bezzi et al. 2001). Lymphangi-

Globular peripheral enhancement with centripetal progression is evident (arrows) at 30 s (b) and 6 min (c) after microbubble injection at cadence contrast pulse sequence. The same pattern (arrow) is confi rmed on contrast-enhanced CT during the arte- rial (d) and late (e) phases. (From the editor, E. Quaia).

a b

c

d e

omas are avascular on colour Doppler and do not enhance with microbubbles. CT demonstrates lym- phangiomas as typically subcapsular low-attenua- tion non-enhancing septate lesions. The presence of curvilinear mural calcification is highly suggestive of lymphangioma (Pistoia and Markowitz 1988).

14.3.3

Malignant Focal Splenic Lesions

Malignant splenic tumours are uncommon. Primary lymphoma and angiosarcoma are well recognized but rare. Metastases most commonly occur from lymphoma, breast, ovary, bronchus and stomach.

Fig. 14.11. a A splenic hamartoma (arrows) is seen as a slightly lower echogenicity focal lesion on B-mode ultrasound. b On colour Doppler imaging, fl ow is seen in a radial distribution (arrows). c Three minutes after Levovist injection, imaging using a late-phase destructive mode (Agent Detection Imaging; ADI, Acuson-Siemens, USA) demonstrates microbubble uptake in the hamartoma (arrow). d Contrast-enhanced CT showing a complex lobulated lesion with variable enhancement (arrow).

Reproduced with permission from Peddu et al. Clin Rad 2004; 59 777-792.

a b

c d

Lymphoma

Malignant lymphoma is the most common cause of

splenic infiltration. The typical US appearances are

of echo-poor focal lesions that may be difficult to

distinguish from cysts (Wernecke et al. 1987; Gorg

et al. 1990). The borders of the lesions may be poorly

defined. ‘Target sign’ lesions and echogenic lesions

have been described (Wernecke et al. 1987; Gorg

et al. 1990). Typically Hodgkin’s and low-grade non-

Hodgkin’s lymphomas result in diffuse infiltration

or focal lesions less than 3 cm in size (Fig. 14.13). By

comparison, high-grade non-Hodgkin’s lymphoma

causes focal lesions of greater than 3 cm in size (Gorg

et al. 1990, 1991) (Fig. 14.14). With microbubbles,

Fig. 14.12. a A cystic, septate lesion in the upper aspect of the spleen (arrow) demonstrating features of a lymphangioma. b Post SonoVue (Bracco, Italy) imaging using a low mechanical index technique (Coherent Contrast Imaging, CCI, Acuson-Sie- mens, USA) defi nes the septate cystic lesion. c Contrast-enhanced CT of the lymphangioma clearly depicts the septations (arrows).

Reproduced with permission from Peddu et al. Clin Rad 2004;

59 777-792.

a

b c

Fig. 14.13a,b. Case of Hodgkin’s lymphoma. a Imaging in the phase-inversion mode (ATL-Philips, USA) 3 min after Levo- vist injection, showing multiple subcentimetre splenic lesions (arrows). No focal abnormality could be demonstrated on B- mode ultrasound (not shown). b Contrast-enhanced CT in the same patient shows no focal splenic lesions.

a

b

irregular peripheral enhancement is seen, with the lesions appearing as defects in the late phase.

Metastases

Splenic metastases are rare: they are found in 7%

of post-mortems in patients with metastatic carci- nomas, and 8% of all splenic lesions were shown to be metastases in one series (Gorg et al. 1991).

The spleen may be involved by direct tumour inva- sion in pancreatic tail, colon, stomach, bronchial and diaphragmatic carcinomas. The US appear- ances are variable, with echo-poor metastases being the most common (Gorg et al. 1990, 1991, 1994;

Solbiati et al. 1983). Echogenic metastases are the least common (Mittelstaed and Partain 1980) and target lesions are less common than in the liver.

Serosal metastases from ovarian carcinoma result in scalloping of the splenic margin. On Doppler, metas- tases are usually avascular. Imaging with micro- bubbles may show variable peripheral enhancement, with lesions appearing as defects surrounded by normally enhancing splenic parenchyma. Metas- tases may be revealed that are not seen on baseline B-mode (Harvey et al. 2000) (Figs. 14.15, 14.16) by increasing their conspicuity. This improves detec- tion and facilitates the identification of subcentime- tre metastases that would otherwise remain occult.

Fig. 14.14a–c. Case of non-Hodgkin’s lymphoma. a Baseline B-mode US showing a complex echo-poor lesion (arrow). b Imaging in phase-inver- sion mode (ATL-Philips, USA) 3 min after Levovist injection, showing irregular peripheral microbubble uptake with the lesions appearing as defects that are more conspicuous than on B-mode. c Contrast- enhanced CT in the same patient shows multifocal hypodense splenic lesions (arrows).

a b

c

Fig. 14.15a,b. Splenic metastases from melanoma. a Three minutes after Levovist injection, imaging using a late-phase destruc- tive mode (Agent Detection Imaging; ADI, Acuson-Siemens, USA) demonstrates two metastases as defects (arrows) surrounded by normal splenic microbubble uptake. b When the colour overlay is removed, no corresponding B-mode lesions could be identifi ed. This case demonstrates that imaging of the late splenic-specifi c phase of Levovist improves the detection of occult metastases by increasing their conspicuity.

a b

Fig. 14.16a-c. Splenic metastases from renal cell carcinoma.

Two focal lesions (arrows) are identifi ed in the splenic paren- chyma on baseline US (a). The lesions become much more conspicuous (arrows) 120 s after microbubble injection at phase inversion more (ATL-Philips, USA) (b,c). (From the editor, E. Quaia).

a b

c

14.3.4

Splenic Infarction

Splenic infarction may result from emboli (endocar- ditis), hyperviscosity syndromes, sickle cell disease and myeloproliferative disorders. On B-mode, acute infarction is ill-defined, characteristically peripheral, wedge shaped and echo-poor (Maresca et al. 1986;

Gorg and Schwerk 1990; Gorg et al. 1990, 1991, 1994; Wan et al. 2000). On colour Doppler, absent signals confirm the diagnosis. Chronic infarction is seen as an echogenic area due to fibrotic change or calcification with overlying cortical retraction secondary to scarring. Microbubbles improve the confidence in diagnosing early infarction with US (Figs. 14.17, 14.18).

14.3.5

Splenic Abscesses

Splenic abscesses on US may be echo-poor, septated and irregularly walled, containing debris and gas (Gorg and Schwerk 1990; Gorg et al. 1990, 1991, 1994;

Wan et al. 2000). They may have variable peripheral vascularity. Microbubbles may show the vascular rim of the abscesses. Common organisms include Myco-

latter have been described as showing a characteristic

‘bull’s eye’ appearance with multifocal small lesions (0.5–2 cm in size) consisting of echogenic centres sur- rounded by echo-poor rims (Gorg et al. 1994; Porcel-

Fig 14.17a,b. This 56-year-old man presented with left upper quadrant pain. a B-mode ultrasound appears normal. b Imaging in phase-inversion mode 3 min after Levovist injection shows a wedge-shaped non-enhancing defect consistent with an infarct (arrow), with normal enhancement of the surrounding spleen.

a b

Martin et al. 1998). The detection of these lesions is improved by using a high-frequency linear probe (Murray et al. 1995). US contrast improves the detec- tion of microabscesses by improving their conspicuity against the normal splenic parenchyma (Fig. 14.19).

14.3.6

Heterogeneous Splenic Echotexture

This is seen as multiple tiny (2–3 mm) echogenic foci or just a heterogeneous echo pattern on B-mode US.

It is a non-specific finding typically seen in previ- ous granulomatous infection such as tuberculosis and fungal disease, as well as sarcoidosis (Fig. 14.20) (Kessler et al. 1993), Wegener’s granulomatosis, amyloidosis and Crohn’s disease.

14.4 Summary

US is a reliable method of imaging splenic abnormali-

ties. The introduction of microbubbles has further

improved the diagnostic capabilities of US, allowing

the investigation of splenic enhancement patterns and

characterization of focal lesions. US imaging with con-

trast is useful in distinguishing splenunculi from lymph

nodes, demonstrating the characteristic enhancement

patterns in haemangiomas, improving the visualiza-

tion of splenic infarction and improving the detection

of microabscesses and focal malignancies.

Fig. 14.18a–d. Splenic perfusion defects in an enlarged spleen. Baseline US (a) reveals an enlarged spleen with one wedge-shaped splenic perfusion defect (arrows) with the base on the splenic capsule, which becomes much more conspicuous (arrows) 100 s after microbubble injection (b). Two further splenic infarcts become evident after microbubble injection, during the late phase at cadence contrast pulse sequence (arrows c, d). (From the editor, E. Quaia).

a b

c d

Fig. 14.19. a B-mode US of the spleen in a patient with disseminated tuberculosis. An echo-poor mycobacterial abscess is seen (arrow). b Post-microbubble contrast media imaging (Levovist) using the phase-inversion mode (ATL-Philips, USA) increases the conspicuity of the lesion (arrow), which is surrounded by normally enhancing spleen.

a b

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Abdominal Applications:

Kidneys